College Level Geology by AudioLearn

COLLEGE LEVEL geology

College Level

GEOLOGY

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TABLE OF CONTENTS Preface........................................................................................................ 1 Chapter 1: Introducing Geologic Terms ....................................................... 1 Basic Geology Terminology ............................................................................................. 1 A through D: ................................................................................................................. 1 E through H: ................................................................................................................. 4 I through M: ................................................................................................................. 6 N through R: ................................................................................................................. 8 S through Z: ................................................................................................................ 10 Rock Types and What they Mean .................................................................................. 12 Key Points in this Chapter ............................................................................................. 16 Chapter 1: Questions and Answers .................................................................................17 Chapter 2: Earth Then and Now ................................................................ 19 First Conditions on Earth .............................................................................................. 19 The Oxygen Catastrophe ................................................................................................ 23 The Earth's Spheres ....................................................................................................... 24 The Internal Earth ......................................................................................................... 26 The Crust ........................................................................................................................ 28 The Mantle ..................................................................................................................... 29 The Outer Core ............................................................................................................... 29 The Inner Core ............................................................................................................... 30 The Rock Cycle ............................................................................................................... 31

Major Features of the Ocean Floor and Continents ...................................................... 32 The Continents ............................................................................................................... 34 Key Points in this Chapter ............................................................................................. 39 Chapter 2: Questions and Answers................................................................................ 40 Chapter 3: Geologic Time .......................................................................... 42 Known Geologic Time Periods ....................................................................................... 42 Proterozoic Era .............................................................................................................. 43 The Paleozoic Era ........................................................................................................... 45 The Mesozoic Era ........................................................................................................... 48 The Cenozoic Era ........................................................................................................... 49 Dating Rocks .................................................................................................................. 50 Fossils and Fossil Types ................................................................................................. 55 Key Points in this Chapter ............................................................................................. 58 Chapter 3: Questions and Answers................................................................................ 59 Chapter 4: Plate Tectonics ......................................................................... 61 Theories of Plate Tectonics from the Beginning ........................................................... 61 Plate Tectonic Basics ...................................................................................................... 63 How do the Plates Move? ............................................................................................... 65 Plate Boundaries......................................................................................................... 65 Examples of these Phenomena in Geology ................................................................ 67 Measuring Plate Motion ............................................................................................. 68 Key Points in this Chapter ............................................................................................. 70 Chapter 4: Questions and Answers.................................................................................71

Chapter 5: Minerals in Detail .................................................................... 73 What is a Mineral in Geology? ....................................................................................... 73 How Minerals Form ....................................................................................................... 78 Classifying Minerals ....................................................................................................... 81 The Mohs Hardness Scale .............................................................................................. 83 More on Silicate Minerals .............................................................................................. 85 Nonsilicate Minerals ...................................................................................................... 86 Key Points in this Chapter ............................................................................................. 89 Chapter 5: Questions and Answers ................................................................................ 90 Chapter 6: Igneous Rocks in Detail ........................................................... 92 What is Magma? ............................................................................................................ 92 How Magma turns to Rock ............................................................................................ 93 Silicates in Igneous Rock ............................................................................................... 96 Igneous Textures ............................................................................................................ 97 How to Name Igneous Rocks ......................................................................................... 98 Intrusive Igneous Rock ................................................................................................ 100 Diamonds and their Origin ...........................................................................................101 Key Points in this Chapter ........................................................................................... 103 Chapter 6: Questions and Answers.............................................................................. 104 Chapter 7: Volcanoes .............................................................................. 106 Early Volcanic Activity ................................................................................................. 106 Volcano Anatomy ......................................................................................................... 107 Types of Volcanoes ....................................................................................................... 109 Different Volcano Characteristics ................................................................................. 111

Volcanic Eruptions ........................................................................................................ 111 Lava Flows and Pyroclastic Flows ................................................................................ 112 Volcano Seismology ...................................................................................................... 116 Key Points in this Chapter ............................................................................................ 118 Chapter 7: Questions and Answers ............................................................................... 119 Chapter 8: Weathering and its Effects on Geology .................................... 121 Mechanical Weathering Types...................................................................................... 121 Types of Chemical Weathering .................................................................................... 123 Weathering Rates ......................................................................................................... 125 Wind and Desert Features ........................................................................................... 126 Soil .................................................................................................................................127 Soil Formation and Classification ............................................................................... 129 Soil Orders.................................................................................................................... 130 Basic Soil Types ............................................................................................................ 132 Ore Deposits and Weathering ...................................................................................... 133 Key Points in this Chapter ........................................................................................... 134 Chapter 8: Questions and Answers ............................................................................. 135 Chapter 9: Sediments and Sedimentary Rocks ......................................... 137 How Sediment Forms ...................................................................................................137 Sedimentary Rock Basics ............................................................................................. 138 Naming Sedimentary Rocks ........................................................................................ 139 Detrital Sedimentary Rocks ......................................................................................... 142 Non-clastic Rocks......................................................................................................... 143 How Sedimentary Rocks are Structured ..................................................................... 144

Sedimentary Rocks and Past Life Forms ..................................................................... 145 Resources we get from Sedimentary Rocks ................................................................. 145 Key Points in this Chapter ........................................................................................... 147 Chapter 9: Questions and Answers.............................................................................. 148 Chapter 10: Metamorphic Rocks in Detail ............................................... 150 How Metamorphism Works ........................................................................................ 150 Metamorphic Textures................................................................................................. 153 Foliated Metamorphic Rocks ................................................................................... 153 Slate ....................................................................................................................... 153 Gneiss .................................................................................................................... 154 Phyllite................................................................................................................... 156 Hornfels+ .............................................................................................................. 156 Schist ......................................................................................................................157 Non-foliated Metamorphic Rocks ............................................................................ 159 Quartzite ................................................................................................................ 159 Marble ................................................................................................................... 160 Conditions of Metamorphism ....................................................................................... 161 Metamorphic Environments........................................................................................ 162 Key Points in this Chapter ........................................................................................... 165 Chapter 10: Questions and Answers ............................................................................ 166 Chapter 11: Earthquakes and Seismology ................................................ 168 Earthquake Definition ................................................................................................. 168 Earthquake Features .....................................................................................................172 Earthquake Measurements ...........................................................................................173 Measuring Magnitude of an Earthquake ..................................................................... 174 Earthquakes Underwater ............................................................................................. 176

Determining Earthquake Locations ............................................................................ 176 Earthquake Predictions ................................................................................................ 177 Key Points in this Chapter ........................................................................................... 178 Chapter 11: Questions and Answers ............................................................................ 179 Chapter 12: Crustal Deformation and Mountains .................................... 182 How Rocks Deform ...................................................................................................... 182 Ductile versus Fragile Rock ......................................................................................... 183 Strike and Dip Explained ............................................................................................. 185 Faults and Joints .......................................................................................................... 186 Rock Folding ................................................................................................................ 189 Folding and Mountain Building .................................................................................. 192 Key Points in this Chapter ........................................................................................... 194 Chapter 12: Questions and Answers ............................................................................ 195 Chapter 13: Effects of Gravity .................................................................. 198 Landslides .................................................................................................................... 198 Components of a Landslide ......................................................................................... 199 Types of Landslides ..................................................................................................... 200 Can Landslides be Predicted? ......................................................................................202 Earth Flows ............................................................................................................... 203 Avalanches ................................................................................................................204 Key Points in this Chapter ...........................................................................................206 Chapter 13: Questions and Answers ............................................................................ 207 Chapter 14: Water and Geology ............................................................... 210 Water in the Study of Geology ..................................................................................... 210

Water Basins ................................................................................................................ 212 Surface Water Explained ............................................................................................. 213 Fluvial Processes .......................................................................................................... 215 Sediment in Streams .................................................................................................... 216 Channel Types in Streams ............................................................................................217 Deltas............................................................................................................................ 218 Water under the Ground.............................................................................................. 218 Hydrology-based Earth Features .................................................................................220 Coastlines ..................................................................................................................... 221 Geothermal Features ................................................................................................... 224 Key Points in this Chapter ........................................................................................... 226 Chapter 14: Questions and Answers ............................................................................ 227 Chapter 15: Glaciers and Glaciation ........................................................ 230 Glaciers and their Formation....................................................................................... 230 How Glaciers Move ...................................................................................................... 231 Glacial Budget .............................................................................................................. 231 Landforms caused by Glaciers ..................................................................................... 232 Glacial Lakes ................................................................................................................ 234 Key Points in this Chapter ........................................................................................... 236 Chapter 15: Questions and Answers ............................................................................ 237 Summary ................................................................................................ 240 Course Questions .................................................................................... 244 Answers to Questions.............................................................................. 285 Answers to Chapter 1 ................................................................................................... 285

Answers to Chapter 2 ................................................................................................... 286 Answers to Chapter 3 ................................................................................................... 287 Answers to Chapter 4 ...................................................................................................288 Answers to Chapter 5 ................................................................................................... 289 Answers to Chapter 6 ...................................................................................................290 Answers to Chapter 7 ................................................................................................... 291 Answers to Chapter 8 ................................................................................................... 292 Answers to Chapter 9 ................................................................................................... 293 Answers to Chapter 10 ................................................................................................. 294 Answers to Chapter 11 .................................................................................................. 295 Answers to Chapter 12 ................................................................................................. 296 Answers to Chapter 13 ................................................................................................. 297 Answers to Chapter 14 ................................................................................................. 298 Answers to Chapter 15 ................................................................................................. 299 Answers to Course Questions ..................................................................................... 300

Is geology a real science, or is it only something of interest to wacky rockhounds? In this college-level course, you will see just how important geology is to the study of the earth when it was first created 4.5 billion years ago and in today's time. You'll see how this planet was first formed and follow it through to more modern times when things like weathering, wave action, and global warming are still impacting the landscape around you. Not only will you be able to name many types of rocks and minerals, you will understand the mystery of why each rock on the ground is so unique. You will also learn why geology is so much more than rocks – it’s really the science of our entire planet all packed into one fascinating audio-course!

PREFACE If you are taking this course because you like rocks and want to learn more about them, you have come to the right place. By the end of this course, you'll understand more about rocks than you thought there was to know about them. If you decided to take this course because you want to learn about geology as a college subject, you have come to the right place. This is because geology is much more than just rocks; this course covers it all. You will learn about early earth as it existed billions of years ago and how rocks are created in the first place. This will take you further onto lessons about volcanoes and how they create igneous rocks, glaciation, how rivers and lakes help form sediment to make sedimentary rocks, how to date rocks, and how wind and weather form rock formations on the earth's surface. Yes, geology is much greater as a subject than can be found in a simple rock. By the end of the course, you will have a new appreciation for every rock you see – even the ugly ones that probably reveal tiny sea creatures embedded within them. You will know why boulders sit in the middle of a field and why certain rocks have lines or speckles in them. All of this you will know from a much deeper perspective as you study geology from the most basic terms to the understanding of complex concepts regarding rock formation. Geology is a complicated topic and one that has a lot of terminologies to study before you can get into more complex topics. In chapter one, you will begin to learn some of the terms you need to know to make sense of everything in geology. You also need to know the basic types of rocks and how they become the size, shape, and color you see when you pick them up off the ground. This chapter gets your feet wet in the study of geology. Chapter two begins a discussion of planet earth and its rocky surface by looking directly at its origins. The earth is about 4.54 billion years old and began as a giant cloud of swirling space dust. Fortunately, it has changed a lot since then. We'll look at how all

that dust collected into the wide range of rocks, minerals, and amazing geological structures on land and sea we now research in geology. At the end of the chapter, you will learn about the continental features and seafloor landscape and why they exist as they do now. Chapter three examines the concept of geologic time. This time dates back to the first days when the earth's crust was being developed. Older rocks look different from younger rocks; you need to know the difference between them. You will learn how to date rocks and how you can use rocks to indicate the age of fossils. The chapter also looks at the different types of fascinating fossils you can find in your own back yard or nearby rock quarry. Chapter four will involve a discussion of what we know about plate tectonics. It is still called "plate tectonic theory" even though there aren't any legitimate counter-theories on why the continents exist at all and where they are located. What plate tectonics means for geologists is that the earth is still changing and phenomena like earthquakes and mountain-building can be easily explained by understanding how the lithosphere moves on this planet. Chapter five in the course begins to talk about what many people think geology is all about – cool rocks and minerals. A mineral is a hardened substance from the earth that is made from single element or just a few elements in a chemical compound. The two main mineral classifications are the silicates and non-silicates. You will learn how to classify and identify the most common minerals you'll find around the world and even in your own backyard. In chapter six of the we get into detail on the subject of igneous rocks and their formation. Igneous rocks are literally born out of fire – the first rocks to be spit out of our molten interior. After reading this chapter, you will understand what's in magma and how it turn into the rocks you see all the time. Magma is more than just underground lava. You will see the amazing things that happen when it cools and the ways the minerals precipitate out of it when that occurs. Chapter seven delves into volcanism and the volcanoes we have on earth. Volcanoes help dispel the heat from inside our planet and contribute to new land formation in some

parts of the world. Magma is extruded from deep within the earth through volcanic activity. You will see the difference between lava and magma in this chapter and you will learn that there are several types of volcanoes and volcanic eruptions all over the world. We will also discuss how volcanic eruptions might be predicted. Chapter eight covers weathering and its effects on geology. Weathering is inevitable and can change rock faces in different ways. You will learn how these work with regard to sedimentary rocks and how weathering creates soil. Soil is different all over the world for many reasons. You will see how soil forms and what makes each soil type unique. Weathering can create metal ore deposits, as you will soon learn. Chapter nine allows you to learn about sedimentary rocks. If igneous rocks are basically the primary rocks, then sedimentary rocks are secondary. These are the rocks that start out as smaller pieces called sediments, becoming lithified to form their own kind of stone. You'll learn how to name sedimentary rocks and what we gain economically from products these types of rocks provide us on earth. Chapter ten rounds out the discussion of rock types by revealing how we get metamorphic rock. Pressure and heat cause metamorphic change in rocks, leading to many different rock types. You will soon understand from this chapter the complexities of metamorphism and how they lead to several types of new rock from old rock. Chapter eleven in the course is about earthquakes. Studying earthquakes reminds us that geology isn't just about rocks. Earthquakes are perhaps the best proof that plate tectonics is not theoretical. They happen mainly when two or more plates are moving in directions that are not congruent with one another. You will learn how earthquakes are measured and see why they cause so much damage. Chapter twelve teaches you how and why rocks are deformed. Rocks seem so solid and yet the awesome powers of earth movement can create giant mountains and crush sedimentary rock into much harder metamorphic rock. You will learn the patterns of rock deformation and the types of stress the earth's crust is under on a daily basis. It will help you understand why the earth has the interesting topography it has now, and see that it will probably continue to have changing topography in the future.

Chapter thirteen in the course helps you understand better the geological phenomena seen due to the effects of gravity. Gravity pulls everything toward the center of the earth so heavy things that don't have the necessary friction or infrastructure to hold up properly will fall down. Rock, dirt, sediment, snow, and ice all participate in this process to create things like landslides, mudslides, flows, and even avalanches. You'll see that there are more forces at play in these gravity-based situations besides the law of gravity. Chapter fourteen is about water; it is important to study water in any course on geology mainly because water shapes geologic structures to a huge degree. Water is contained in the hydrosphere but it interacts with the geosphere all over the world. You'll learn about streams, rivers, deltas, and basins and why they are critical parts of the geology of the earth. Chapter fifteen in the course covers glaciers and how they shape the geomorphology of the earth. Glaciers represent the cryosphere of the earth. You'll learn how important glaciers have been in shaping the land and water features in all continents of the planet. Let's dig right in and study the fascinating science of our rocky earth!

CHAPTER 1: INTRODUCING GEOLOGIC TERMS It is hard to study any complex topic without knowing the lingo. In this chapter, we will start by discussing some of the most important terminology you need to know to get started in the study of geology. All terms will be explained in detail later in the course; this is just a chance to get your feet wet. We will also talk about the three basic types of rock and how they become the color and shape they are when you see them on the ground.

BASIC GEOLOGY TERMINOLOGY There are so many terms in geology that you may not understand. For this reason, we will begin this course by looking at the basic terms you need to know to get started. Almost all of the terms will be very familiar to you by the end of this course. Here are some terms you don't have to memorize but should familiarize yourself with:

A THROUGH D: •

Abrasion – when rocks are worn down by other rocks or minerals, especially during transport.

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Andesite – an igneous rock that is gray and fine-grained; made from thick, viscous lava.

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Anticline – a fold of rock that bulges up in the middle.

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Attrition – the wearing down of rock grains or pebbles during transport.

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Basalt – igneous rock that is black and fine-grained; usually made from thin lava.

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Batholith – a large intrusion of some type of igneous rock (often granite) that is formed so far beneath the surface that it cooled extremely slowly.

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Bedding or bedding planes – this involves the layering of sedimentary rocks so you can see the layer boundaries (called bedding planes).

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Bed load – this is the sand and gravel that gets carried own a river from changes in salt content and by traction.

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Boulder clay – a mixture of clay, pebbles, and boulders deposited by ice sheets (like glaciers).

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Calcite – a common "fizzy" mineral that fizzes when exposed to dilute acid. This is actually calcium carbonate and is what makes up most limestone.

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Cementation – when sediment grains are stuck together by minerals that were once in a liquid solution and then precipitated out to make sedimentary rock.

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Chalk – this is limestone made from microscopic pieces of calcium created by planktonic algae (the tiny pieces of calcium are called coccoliths).

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Coal – compressed sedimentary rock made from plant material that was carbonized over millions of years underground.

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Coarse-grained rock – what you call a rock with grains that are at least the size of peas.

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Columnar joints – these are cracks made from long pillars or columns of rock that are made when lava flows begin to cool.

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Conglomerate – what a rock is called if pebbles or boulders have been cemented for various reasons.

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Continental shelf – this is where the ocean is less than 200 meters deep near the edge of a continent.

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Contraction – what happens to rock when it shrinks during cooling.

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Contact metamorphism – this is metamorphism that happens when there is a lot of heat near hot magma.

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Creep – this is when small pebbles slide across desert lands from high winds across the desert.

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Cross-bedding – this happens when layers are formed on some angle because sediment has become deposited under the influence of wind or flowing water.

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Crystal – the regular ordering of a mineral due to its ionic structure. A crystal will generally split along a plane of some kind.

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Crystalline stone – this is any rock or stone made from crystals that are interlocking. Most igneous and metamorphic rocks are considered crystalline.

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Crystallization – this is when a solid substance that is often a crystal was once in solution but precipitates out of solution. It happens when seawater evaporates or when crystals form during the cooling of hot lava.

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Deformation – this is when there are forces that act on rocks to change something about their shape.

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Delta -this is the end of a river near the sea where it breaks into many channels, depositing sediment it disgorges out its mouth.

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Dyke – any intrusion of igneous rock that was formed through the action of magma flowing through other rocks or faults in rocks, so that it cuts through the different rock layers.

E THROUGH H: •

Effusive eruption – this is when a volcano erupts, giving rise to hot and liquid lava rather than gas and ash.

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Erratic – this is a large rock or boulder carried a long distance from its origin after having been deposited by a retreating glacier.

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Estuary – the part of a river's mouth that experiences tides.

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Erosion – this is different from weathering and happens when moving ice, wind, or flowing water breaks down rock.

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Exfoliation – this is when surface rock is peeled away over time from weathering, layer by layer.

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Explosive eruption – this is when a volcano erupts to give rise to gas, bombs of pumice, ash, and other thick materials.

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Extrusive rocks – these are rocks that are made from eruptions of something at the surface of the earth.

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Faults – these are deep lines in the earth where movement of large chunks of earth can happen. Expect to see different rock types on either side of any Faultline.

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Feldspar – this is a common type of mineral you might see in igneous and sometimes in metamorphic rocks.

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Fine-grained rocks – these are those where the grains in the rock are too small to be seen with the naked eye. These are less than 0.1 mm in diameter.

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Floodplain – this is the flat land around a river or floor of a valley that can easily flood after a heavy rainfall.

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Folds – these are places where rock layers are bent through the compression by other rocks. This is how mountains get built at the time tectonic plates collide with one another.

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Foliated or foliation – this is when metamorphic rocks like schist line up in the same direction or are compressed into a flattened texture.

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Fragmental or clastic – this is when grains of sediment are made from erosion occurring after more ancient rocks or seashells have acted on them.

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Gabbro – dark and coarse-grained igneous rock made by slow cooling of lava. It is the same as basalt but has larger intrusions.

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Gneiss – this is metamorphic rock that is coarse-grained and often banded as darker and lighter elements are layered out.

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Grains – these are mineral crystals or particles of sediment you see in all types of rocks.

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Granite – this is light-gray or pink, coarse-grained igneous rock made by slow cooling so large intrusions are found. This is the same as pumice but is a lot harder.

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Hydrolysis – this is a weathering process involving acid rain that slowly wears away minerals to make clay plus salts that dissolve from the acidity of the rain.

I THROUGH M: •

Igneous rock – these are formed with magma from a volcano and cooled, compressing with intrusions of other things.

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Interlocking rock – this is a rock where grains of minerals or crystals form a mosaic due to their interlocking nature.

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Intrusions – these are areas of igneous rocks that have cooled and later crystallized when magma is cooling deep under the earth.

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Invertebrates – these are animals without any backbone, such as insects, shellfish, and worms.

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Joints – these are cracks you see in rocks due to the release of pressure from erosion above the rock that decrease the weight on them, or shrinkage of rocks. Most joints are vertical.

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Lahar – a mudflow formed from the combination of water and volcanic ash. This can damage large areas of land and homes.

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Landslide – any mass movement of rocks and earth down some type of slope. Mudflows, rock falls, and landslips are all types of landslides. A Landslip is similar but often involves clay that slips on an already-defined surface.

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Lava – this is molten basalt rock that has escaped from a volcano. Magma is not the same thing as lava.

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Limestone – this is sedimentary rock made mostly of calcium carbonate and formed when marine animals with shells die.

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Lithosphere – this is the main outer layer of the earth containing the top part of the mantle and the earth's crust.

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Longshore drift – this is movement of any type of sediment due to wave action near a shoreline.

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Magma – this is the molten rock containing mostly dissolved gases from a volcano that resides beneath the surface of the earth.

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Marble – this is a type of metamorphic rock that is made out of limestone.

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Medium-grained – this is a rock where the grains in it are of any type and are between microscopic and pea-sized in nature.

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Metamorphic rock – a rock type where the rock was once one type but was reshaped later due to any combination of heat and pressure.

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Metamorphic areole – any area around an intrusion where hot magma managed to heat and then alter the surrounding rocks.

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Metamorphism – the process altering a rock from one form to another through heat, pressure, or both.

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Mineral – any natural compound that crystallizes with a regular structure.

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Mica – a type of mineral that is flaky and shiny. You will see it in schist, gneiss, and granite mainly.

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Moraine – this is rocky material that is carried in a glacier and gets dumped in a spot wherever the glacier has retreated and melted.

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Mudstone – soft rock actually made of fine clay that is compressed later. This is also known as shale.

N THROUGH R: •

Oolith – this is a small, round piece of calcium carbonate made through the rolling wave action of water in shallow seas.

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Oolitic limestone – this is limestone you see with small grains in it called ooliths. It is made when calcium carbonate precipitates in warm seawater near the shallow coastline.

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Oxidation – a chemical process occurring between certain metal elements and oxygen. It is what happens to make rust-colored oxides and "rust" out of surface iron deposits.

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Pahoehoe – this is the Hawaiian name for the ropy surface lava formed in a skin that folds into twisty shapes while hotter lava flows beneath it.

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Pebbles – a rock piece that is usually round and less than 10 cm in total size (but usually larger than 1 cm).

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Pele's hair -this is a form of lava that forms a fine stringy pattern as it cools rapidly so it looks like hair.

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Physical weathering – this is the type of weathering that happens from mechanical breakdown of surface rocks.

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Pillow lava – this is lava that looks like pillows formed when it comes into contact with cold seawater. It comes up from the seafloor.

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Plate tectonics – this describes the very slow motion of the major ridge plates on the earth's lithosphere.

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Playa – this is a lake you might see in a desert that is only temporary. Usually these are seen dried out unless there has been recent rainfall.

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Plucking – this is a glacial term where rock at the base of a glacier gets eroded from a combination of icing and movement.

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Porous – this is a phenomenon where sedimentary rock (mostly) has spaces that have filled in with groundwater.

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Pumice – extremely lightweight igneous rock made from gas-rich magma that has erupted under explosive conditions.

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Pyroclastic and pyroclastic flow – this is when hot gases and ash with rock are erupted from a volcano, rushing down the hillside at more than 100 miles per hour. The term "pyroclastic" refers to this rock and ash.

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Quartz – this is white or gray glassy material sometimes seen within granite. It is made from silicon dioxide.

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Quartzite – this is extremely hard, nearly white sandstone that is actually quartz grains that have become completely cemented together.

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Re-crystallization – this is when a mineral changes form from something like clay to a form such as mica. This occurs because of a chemical change in the rock and not because of melting or dissolving.

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Regional metamorphism – large-scale metamorphic changes in rocks because of widespread heat and pressure changes (the kind that builds mountains are an example).

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Rhyolite – a type of igneous rock with fine grains made from extremely thick lava.

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Rock salt – this is sodium chloride that came from the sea at one time but evaporated and got incorporated into certain rocks.

S THROUGH Z: •

Salt – this is any ionic compound that dissolves in water. Calcium salts and sodium salts are commonly discussed in geology.

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Saltation – this is when sand grains bounce along because of the activities of flowing water or windy conditions.

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Sand – these are tiny particles up to 2 mm in diameter that are made from quartz and resistant to most chemical breakdown techniques.

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Sandstone – this is sedimentary rock that has medium grains within its structure and that consists of cemented sand grains.

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Schist – this is metamorphic rock that has shiny mica in it that is arranged in a foliated way.

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Sea-stack – this is a tall pillar of rock you can see coming up out of the sea and worn into a pillar by the action of waves eroding the rock.

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Sediment – this is any type of material that layers out due to the action of standing water and gravity. This can be anything – sand, organic material, shells, mud, or pebbles. Sediment may or may not become rock.

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Sedimentary rock – are formed on or near the Earth's surface from the compression of ocean sediments or other processes.

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Shale – this is a rock that was compressed to make dark-colored, grayish sedimentary rock. Expect to see fine, microscopic grains.

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Sill – this is an intrusion or influx of igneous rock that has seeped in along the planes of other rock layers.

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Slate – this is metamorphic rock made through compression of mudstone.

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Soil creep – this is mass movement that happens gradually due to gravity on steeper mountains or hillsides.

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Strata – these are any layers you see within rock itself, usually made by sediment of some kind. 10

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Strike-slip fault – this is a fault that involves a section of rock that moves past another in a horizontal fashion.

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Suspension load – this is a load of clay or other fine particles that get carried through the action of water and wind; they settle out eventually when the conditions are less fierce.

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Syncline – this is when a rock has bulged in a downward fashion or appears sunken in the middle.

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Tectonic forces – these are those forces that either crush or stretch the surface of the earth. This leads to faults, mountain building, and folding or shearing of the earth.

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Tectonic plates – these are stiff or rigid sections of the earth's crust that move independently from other plates.

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Texture – rock texture is described completely according to the size of the grains in the rock itself and the rock's shape due to the presence or absence of weathering and other factors.

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Thrust fault – this is often called a reverse fault because large sections of rock have slid up and over another section of rock.

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Unconformity – this involves the boundary layer between two separate rock sections that have cut across one another, leading to an apparent gap in geological time.

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Uplift – this is when a section of the earth's crust is squashed by tectonic plate activity or perhaps by ice sheets that have melted in varying ways.

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Vent – this is often seen in volcanic craters and is where gases and magma erupt to allow contents beneath it to escape.

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Vesicles – these are bubbles of rock that are made when gases beneath the earth are emitted from volcanoes. The lava cools and freezes the lava into vesicles.

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Volcanic ash and gases – these are the "stuff" emitted from a volcano. Gases are often made from carbon dioxide, water vapor, and sulfur gases. 11

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Wave-cut platform – this is a flattened area of rock that has become eroded by tide and waves, usually existing between high and low tidal areas.

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Weathering – this is rock breakdown for any reason, such as mechanical, biological, and chemical forces.

Wow, that's a bunch of terms! Don't worry if you haven't gotten them all because you will gradually have a deeper appreciation for what they mean.

ROCK TYPES AND WHAT THEY MEAN While every rock is unique and different, this doesn't mean that you can't categorize them in some way. There are actually only three major types of rocks. These are igneous, sedimentary, and metamorphic rocks. The term igneous refers to "fire" or molten lava. Rocks of this type of form only when hot lava cools into rock. Particles can settle as this happens or minerals can precipitate to create something more interesting than a black rock. Look for different mineral grain sizes and textures. The texture depends on how slowly or quickly the lava cools. Larger crystals come from slower-cooling lava and vice versa. Some interesting options among these: •

Granite pegmatite – this is igneous rock formed near the top of a magma chamber. It has many possible colors, including quartz gray, white, pink, and dark-colored mica.

•

Diabase – this is rock solidifying just below the earth's surface. It cools rapidly, giving rise to a salt and pepper appearance. Basalt and gabbro are identical but differ in the size of the crystals. Diabase is in-between the two. Gabbro has the largest inclusions. Figure 1 shows a boulder with some diabase and gabbro in it:

Figure 1.

•

Diorite – this is rock that crystalized in a mountainous area where black hornblende and white plagioclase come together. Like diabase, it is black and white.

Sedimentary rocks are layered in some way. They are made whenever rock particles or other minerals settle out from within the water or air. Minerals can also simply precipitate out of solution at varying times or concentrations, giving rise to a layered look. Lithification is when these layers become rock. Here are some interesting choices: •

Limestone – limestone is extremely common. It comes from organisms that have shells or other calcium carbonate-containing structures. These settle out as organisms die off to make layered limestone in shallow waters. Figure 2 is a good image of limestone:

Figure 2.

•

Shale – shale is made from fine silt and clay that gets deposited in slow moving waters, often outside of river deltas where water cannot keep particles within it. Shale settles out as a grayish material in these waters. The layers flake off each other easily.

•

Sandstone – this is made from sand that builds up in waters that is quickly moving. It will also layer out in desert areas, eventually forming fine-grained sandstone.

Metamorphic rocks are either igneous or sedimentary or both at some point but get changed due to pressure, heat, or chemical reactions. Minerals and texture help define these rocks. These are rocks with different grain sizes and layering orientations compared to what they were. Foliation is seen in these rocks, which is a deformation of the shape of intrusions/grains due to pressure forces. Some interesting examples include these:

•

Manhattan schist – this is rock that was once shale and now has fine grains of biotite along with gray quartz or white orthoclase. The layering comes from compression on the shale.

•

Gneiss – this used to be granite but became deformed by applied pressure and heat to make layers that are even-grained but more layered than the original rocks. Figure 3 shows what gneiss might look like:

Figure 3.

KEY POINTS IN THIS CHAPTER •

Review the terms and sort out which represent processes involved in geography, which are structures involved in geography, and which are just types of rock.

•

The three main types of rock are igneous, metamorphic and sedimentary.

•

Rocks get acted on by chemical, mechanical, and biological forces to change them.

•

Sediment can get layered out in air or water.

•

All magma eventually cools with grains that depend on the rate of cooling. High rate means small grains, while low rates of cooling lead to larger grains.

•

Pay attention to colors in rock as many represent a type of mineral.

CHAPTER 1: QUESTIONS AND ANSWERS 1.

What form of lava looks like thick ropes of smooth hardened lava? A. Aa B. Pahoehoe C. Basalt D. Pele's hair

What is light-weight gas-filled cooled lava called? A. Basalt B. Diorite C. Pumice D. Intrusion

Areas of igneous rock that crystallize and are seen in rocks after they cool are called what? A. Intrusions B. Anticlines C. Synclines D. Joints

From where do you see most magma reaching the earth's surface? A. Tidal pools B. Tectonic plates C. Earthquakes D. Volcanoes

What type of rock would you see foliation in the most? A. Diorite B. Granite C. Schist D. Sandstone

What is the dangerous emission from volcanoes that travels quickly at 100 miles per hour or more down the volcano's side, made of both gases and ash called? A. Magma B. Pyroclastic C. Playa D. Pele's hair

What type of grayish rock is made in shallow waters outside of river deltas as the stuff suspended in the river merges into slower moving waters? A. Shale B. Limestone C. Sandstone D. Bedrock

What activity or process most creates mountains around earth? A. Vulcanism B. Weathering C. Unconformity D. Plate tectonics

What process specifically acts on rock due to acid rain? A. Oxidation B. Saltation C. Hydrolysis D. Plucking

10.

Which type of rock might you see foliation as part of its structure? A. Igneous rock B. Metamorphic rock C. Feldspar D. Porous rock

CHAPTER 2: EARTH THEN AND NOW This chapter begins a discussion of planet earth and its rocky surface by looking directly at its origins. The earth is about 4.54 billion years old and began as a giant cloud of swirling space dust. Fortunately, it has changed a lot since then. We'll look at how all that dust collected into the wide range of rocks, minerals, and amazing geological structures on land and sea we now have the privilege of looking at and studying every day. At the end of the chapter, you will learn about the continental features and seafloor landscape as well as why they exist as they do now.

FIRST CONDITIONS ON EARTH Earth is so old that it took almost a billion years for the first evidence of life to show up. It started out as a collection of dust and gas swirling around from what was left over from the same stuff that made the sun. A solar nebula was "in the area" and began to swirl in a disc-like shape. The sun formed first, and the planets followed shortly thereafter – all as swirling balls of dust and gas. The earth came together and was very hot and molten in the beginning. As the galactic dust collected, pressure built in upon itself due to the effects of gravity. Gravity happens only as the dust in the middle gets pressed on and heated by the burning sun. This molten ball cooled most on the outside to form a solid crust on the outside. This crust formed only when water became present and started to cool the surface of earth. The moon didn't begin until the earth developed its crust, possibly because a small planetoid struck the earth, causing the tilt of our planet, perhaps. The moon is about 4.4 billion of years old. Our first atmosphere would have been bad to breathe in. It had little oxygen and was formed from what's called outgassing. This term refers to the emission of gases from volcanic activity on earth. Water eventually condensed to form liquid water and ice

probably got deposited by passing comets. This is how we got the oceans around the planet. It is likely that water was present from earth's earliest years. We call the first part of earth's lifespan as the Precambrian era. It is sometimes called the cryptozoic era. This era accounts for 88% of the geological time of the Earth. There are three eons in the Precambrian era. These are the Hadean, Archean, and Proterozoic eons. These all end about half a billion years ago (exactly 541 million years, actually), when so many hard-shelled organisms first began to show up on earth. There isn't much fossil records showing anything from Precambrian earth. Most rocks of this time have metamorphosed or been altered since then so even the origins of possible fossils are obscure. In the beginning, the material coalesced and was probably struck by a small planet or "planetoid" we call Theia. This impact broke pieces off of earth and Theia to form the moon. We know that the earth's crust is about that old due to the fact that zircon crystals were found in Australia that dated from that time. Carbon was found in rocks that are at least 3.8 billion years of age. Most carbon comes from living things so this may be when life first originated. Other theories indicate that early life may have begun as many as 4.280 billion years ago. Most of this early life was in the ocean and most developed as soft-bodied creatures that had no skeletons or shells. The Hadean Era was a lot like what you'd imagine Hades to be like. The earth was just formed and was molten. Imagine a world with oceans filled with liquid rock, impact craters from outer space, and boiling sulfur gases. Volcanoes were not high like they are today because they had nothing to build on; instead, they were just cauldrons where gas and molten lava spilt out or were ejected. Meteors were impacting all the time because we didn't have the atmosphere, we now have to burn these up. About 6100 meteors reach the ground on earth each year now and fewer even make it to the ground because of our atmosphere. Imagine not having much of an atmosphere to block them. The atmosphere was mostly water vapor and carbon dioxide, plus tiny amounts of sulfur and nitrogen.

Lava was so prevalent then that it buried any new cooling lava that would otherwise have developed. It's possible that when Theia struck the planet in the early years, the splash itself from molten lava was what actually made the moon. The Archean Era was next. It took about a billion years of having an earth as hot as lava to get to this stage. The earth cooled due to the presence of water vapor and a crust formed. On that crust, the ocean began to develop also. Carbon dioxide actually started to disappear along with the water vapor because it got transformed chemically into limestone, which is calcium carbonate. This layered the floor of the ocean. Nitrogen made up the majority of gas around earth. Clouds and rain fell on the earth during this time and the floor of the ocean was solid. Inside the earth, there is a lot of heat and magma or molten lava to be emitted still from volcanoes. As volcanoes build and cool, they develop height. This height eventually reached the ocean surface to get to form actual islands. These often formed in chains such as the island chains that you see in the Hawaiian Islands, for example. There would be no continents, but the islands would be mobile as they rested on a bed of magma. There were far fewer asteroids and meteorites than before islands bumped into one another to make even bigger chunks of land. It took so many of these collisions plus more volcano building to make the continents. Movement of the continents now and then is called plate tectonics. You will learn much more about this later. Life forms in the Archean period was mostly cyanobacteria, which used to be called blue-green algae. In truth, none of these organisms were bacteria or algae; they were their own kingdom, called Archaea or archaebacteria. On land, there were no living things. The oldest fossils are found in what we call Archaean rocks. These rocks are formed in areas of the continents where the rocks have been relatively stable over time. You commonly see these areas in Northern Canada and Greenland. You will learn about cratons in a little bit. These are considered the early core parts of the continents. It's in these cratons where the oldest rocks currently come from. Sedimentary rocks tended to attach to the edges of these cratons much later in time, making them bigger still. These later rocks got folded up into the existing cratons as two or more collided to form things like mountain ranges or huge dips between cratons that

separated from one another. The middle parts of cratons were mostly igneous rocks and were once mostly lifeless. Continent building is rough; you can imagine how hard it must have been to build up and then squish areas of land until something big enough to be a continent could be created. The oceans in Precambrian areas were not deep but instead covered most of the continental areas with much shallower seas than exist now. At the edges of existing continents, we still have shallower oceanic areas where the geology changes all the time. Sedimentary rocks have taken a particularly long period of time to develop. You had to start with igneous rock that got dissolved, crushed, or suspended in water where waves or other areas of flowing water moved the sediment. Sediment then settled out and compacted into hardened stone in order to make actual sedimentary rocks. Minerals helped to make the different sediments over time. Dense minerals like quartz were broken to make sand that travels only a small way away from shore. Finer pieces of silt were made from other minerals that got carried further out into the sea to make shale. Still, others dissolved in water so they could later form calcium carbonate or lime. Minerals also got dissolved or broke away from igneous rock to later become parts of sediment. You will hear much more about how all of these rocks got created and altered over time. The Proterozoic Era ended just at the time when early life began in earnest. This era lasted from 2.5 billion to 500 million years ago, making the era last about 2 billion years in total. By the end of that time, there were two major supercontinents. They were originally formed by the collisions of endless numbers of minor volcanic islands. The numbers of volcanoes dropped dramatically during that time due to the Earth's cooling over time. There was plenty of life in the ocean and a few single-celled organisms on land. Some multi-celled organisms started to show up just before the end of this era. None of these had shells or skeletons. The atmosphere was unchanged with a lot of nitrogen and carbon dioxide, but this was the beginning of oxygen gas being emitted into the atmosphere by photosynthetic organisms. Oxygen was emitted for a couple billion years before it started to show up in the atmosphre but most was used in chemical reactions or

was dissolved in water. It took a while before this became gaseous and not so toxic to all the lifeforms existing on earth at the time. The glacial ice sheets started to develop and travel down parts of the continents in the Northern Hemisphere. The first time period where glaciation occurred was known as the Gowganda glaciation. The equators were much warmer than the poles, just as is true right now. The history of supercontinents may be different from what you have been taught. You may have heard of Pangaea as the first continent, but this isn't how it all actally began. The first main supercontinent was Vaalbara, existing about 3.6 billion years ago. It broke up to make a supercontinent called Kenorland about 2.8 billion years ago, leading to 4 cratons. These were called the Baltica, Yilgarn, Laurentia, and Kalahari cratons. Still another supercontinent called Nuna or Columbia formed about 2 billion years ago. This broke up to make Rodinia about 1 billion years ago. Pangaea didn't arrive to make up the existing continents until about 335 million years ago.

THE OXYGEN CATASTROPHE The oxygen catastrophe caused a major ecological crisis around the world. Remember that most life forms not only didn't need oxygen, they didn't like it at all. Some oxygen was made into things like iron oxide or rust, while other oxygen atoms went to make other metal oxides. After this happened, oxygen simply had to go somewhere. It went into the atmosphere. When you see large banded areas of rust in rock formations, this is caused by iron oxidation which was rampant on earth. Figure 3A shows a rock that has some of these banded iron oxide layers:

Figure 3A.

The eon of the Proterozoic was once called "Precambrian" but is now just a portion of what we now call the entire time before the Cambrian boundary. This period was itself divided into three eras, called the Neo-, Meso-, and Paleo-proterozoic eras. These correspond to the Precambrian Z, Y, and X rock strata in North America, respectively.

THE EARTH'S SPHERES You have probably heard of the spheres of our atmosphere – like the stratosphere, etcetera. The earth itself is part of that sphere system; this means that the ground itself and parts beneath it are included in these spheres. Honestly, you need all the spheres around earth to work together for Earth's sustainability as a planet. The lithosphere is the "rock" part of the earth. This includes both the interior rocky parts and the rocky surface of earth. The sphere outside of that is the biosphere, which 24

is where everything lives. Alongside of that sphere is the hydrosphere. This is where the water is around earth. Then we have the atmosphere, which has its own set of gases and other features. Lastly, there is the cryosphere, which are the poles and all the ice in it. You can imagine that these interact together in geology. Figure 4 shows you most of these spheres:

Figure 4.

The water around earth is enormous. This water can be either salinized or nonsalinized. Salinized water is water that is salty; this makes up about 96.5 percent of the total water on earth. Water also makes up part of the atmosphere and the cryosphere as well. The cryosphere doesn't seem huge, but it actually locks up about 75 percent of all the fresh water around this planet. You have to think of these spheres in geology. Water in the atmosphere rains onto rocky surfaces, contributing to erosion and other types of weathering, depending on the situation. Acid rain as you know, is a situation where rainfall causes chemical changes in rocks. Rivers and lakes have their own kind of weathering; waves in the ocean help alter sand and the rocks near the shoreline. Ice

itself can seep into tiny cracks in rocks in liquid form and then expand in its ice form to widen these cracks substantially. Just imagine what a glacier can do! The atmosphere is likewise affected by the lithosphere. The fossil fuels we burn all the time (such as gasoline, diesel fuel, and coal) are emitted into the air. These fossil fuels ultimately come from decaying vegetation deep beneath the earth. This was living vegetation millions of years ago but only the carbon and hydrogen in the plants survive as crude oil in the present time. When we burn them, the carbon dioxide, and other gases cause retention of heat around the earth. This changes our various climates and really messes up the rest of the planet because of what we refer to now as "global warming". Global warming affects the rest of the earth's spheres.

THE INTERNAL EARTH Earth is really complex inside. There are several inner layers beneath the part of the earth we see. While we can't go down to the center of the earth, we can do a lot more than we used to so we can figure out what would happen if we did. There are several layers we can identify beneath the earth's outer crust. The crust is just the first outside layer. It's more complicated than you'd think. Inside that is the mantle, which is more fluid than the rocky outer surface. Inside that is an inner core that is very liquid. Finally, you have the solid inner core. This area inside the earth's center must be solid because of the weight of the rest of the earth being so great that it has no choice to be solid. Figure 5 depicts this image for you:

Figure 5.

You can divide these layers differently, depending on who in geology you talk to. There are rheologic divisions that depend on the state of rock (liquid versus solid) and chemical divisions, based on what we know about the internal chemistry of the earth. Rock does not react the same at different pressures and temperatures. This means that you will see something very different a few thousand kilometers below your feet when watching rocky material that far down. These rheologic differences lead to five layers called the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core. It's the chemical variations of the planet that give us the traditional layers called crust, mantle, outer core, and inner core differentiations.

THE CRUST The crust is actually very thin – just 100 kilometers thick on average. The oceanic part of the crust is denser and not as thick as the continental crust. Both float on the mantle but the ocean's crust sits lower than continental crust. This is a good thing because otherwise it would be too high to be called the ocean floor. Crustal density does not equate with thickness; the ocean floor is very thin in some places – so thin that the mantle seeps up there to create new crust. This is especially true in areas like the midPacific near where the Hawaiian Islands are still being built. Other areas where the crust is thicker, mountains build up or there are large inland plates of land lying far inland. These are spots where the crust is most likely to have crumpled up. Inside the crust, the temperature changes from what we experience on the surface to as high as 870 degrees Celsius deep inside. Rock will start to melt in these regions and turn to mantle. The earth has the same area around its surface, which means you cannot make more crust in the deep ocean without removing crust from somewhere else. Mantle gets inserted along the mid-oceanic ridges but is also sinking or subducting below the continental crustal areas. You will learn more about the different plates that float like a jigsaw puzzle on earth and what happens at their edges. The rocks you'll see at the oceanic crust will be basalt, which is mostly just lava that has hardened. The rocks at the continental crust will be like granite. Below the crust, the mantle is like plastic and is somewhat cool. These two parts make up the lithosphere. The asthenosphere is below the lithosphere. It is semisolid like gelatin and hot. It is like the lubricant that helps the lithosphere travel over the mantle. This layer goes to about 700 kilometers deep to earth's surface.

THE MANTLE The mantle makes up about 84 percent of the total volume of the Earth. It starts at what is called the Mohorovicic discontinuity. This is the crust-to-mantle boundary; it is also called the Moho. A discontinuity is where seismic waves deep beneath earth change their velocity. This is about 8 kilometers below the ocean basin surface and about 32 kilometers on average beneath the continental surfaces. Seismic waves speed up here due to its increased density. The discontinuity is where the solid becomes liquid beneath the crust. The mantle itself goes down to about 2890 kilometers beneath your feet. It is hot there – about 500 to 900 degrees Celsius at its coolest and about 4000 degrees Celsius at its hottest. It is thought to be made of a mineral like peridotite or what you'd call peridot but in liquid form. Peridot is a green-colored gemstone.

THE OUTER CORE The earth's core is mostly made of liquid iron and a smaller amount of nickel and lighter elements. It is about 2300 kilometers thick itself and extends to about 3400 kilometers to the earth's center. The distance overall to get to the center is about 6370 kilometers in total. As things settle due to density, the most dense elements settled early in the course of the earth's history. It means that these are nearer to the earth's inner core. There is a general increase in density nearer to the center of the earth because of this feature. The outer core is hot but not totally melty like the mantle. It is also too hot to be thick. The temperatures reach 5730 degrees Celsius. It has a property you should remember. Because it is fluid to some degree but very dense, it spins faster than the rest of the earth. This is a turbulent situation where there is differential spinning velocity of ironcontaining material – enough to make the earth have a nice magnetic field. The spin of the earth leaves north and south magnetic poles that are different by 11.5 degrees or 500 kilometers from our geographic north pole; this is just part of the tilt of the earth. The earth itself is tilted about 23.5 degrees in total.

THE INNER CORE The inner core is in the center of the earth. It is similar to the outer core in some ways. It is made of nickel and iron and is more than 2400 kilometers in diameter. It is extremely dense and under a lot of pressure from all the earth pressing down upon it. It is solid in its center – even though its temperature is high enough to melt metals. You'd see a lot of cool heavy metals in there, such as palladium, platinum, gold, silver, and even tungsten. It is as hot as the surface of the sun here – at about 5400 degrees Celsius.

THE ROCK CYCLE

Figure 6.

The rock cycle is an important piece of information for all geologists. Rocks don't change very easily but over millions and billions of years, rocks actually do change their properties – both physical and chemical. The cycle involves the three main rock types. There is really no beginning or end here – just a cycle. Magma crystallizes or solidifies to make igneous rocks. These can change directly to become metamorphic rocks. They can also erode directly to make sediment that creates sedimentary rocks. Tectonic plates

can get subducted or buried to make magma again, which starts the cycle. Figure 6 depicts these processes together: Let's look at the processes in more detail: Crystallization – this is basically the process of magma hardening into crystals of different kinds. Olivine is a mineral that takes longer to crystallize than quartz. This is why you would have quartz crystals (that are large or small, depending on cooling rates) imbedded in the olivine rock. Erosion and sedimentation – this is a combination of weathering and layering. Weathering will wear rocks down to smaller pieces known as sediments. Ice, water, and gravity carry sediments from one place to another where they layer out over time and density. Denser deposits sink more deeply but not if a less dense deposit has solidified for another reason. You don't get less rock until the sediment has all become compacted down. Metamorphism – the term metamorphism just means "change". Heat and pressure can both change rocks in different ways. If a rock has a unique pattern of any kind, metamorphism has likely taken place. Just remember that metamorphic rock is any kind of rock that has changed its characteristics in some way.

MAJOR FEATURES OF THE OCEAN FLOOR AND CONTINENTS The ocean floor and continents have interesting features that make them different across the world. The ocean floor starts at the continents and then becomes the continental shelf, leading to the continental slope to reach the abyssal plain or flattest section of the ocean floor. Sediment cascades down the continental slope to make it less steep in the area between the continental slope and the abyssal plain. Figure 7 shows these features:

Figure 7.

In the middle of the ocean, you have the mid-ocean ridge, which is like mountains between the continents from bulges and crumpling of the tectonic plates. You also have rift valleys where the ridges have their own valleys between them. Deep trenches are created between tectonic plates that are usually separating. Note that there might be hotspots or volcanic island areas as you see with the Hawaiian Islands. Not all hot spots reach the ocean surface. Abyssal hills and seamounts are where these hotspots have not reached the ocean surface. The ocean itself is divided into zones according to their features, such as temperature, pressure, amount of salt in the water, and amount and type of sea life. Atop the abyssal plain is the abyssal zone, reaching as far down as 6 kilometers. The hadal zone is the deepest at 6 to 11 kilometers. The term MBSF means "meters below the seafloor", is commonly used to describe these numbers. Sediment in the seafloor can be of 4 types: The first is the terrigenous sediment, which is stuff coming from the continents, such as from rivers or rainfall. The second is called the biogenous sediment, coming from the shells you see in marine life. The third is called the hydrogenous sediment, coming from materials dissolved within the ocean whenever the conditions change. The last is the cosmogenous sediment that comes from outer space stuff, such as meteors.

The most abundant source of sediment is the terrigenous material. The biogenous sediment is next, but it takes a thousand years to get about 1 centimeter of this material on the floor of the ocean. Hydrogenous and cosmogenous sediments are much less common. The hydrogenous sediments may be from manganese and other salts that don't dissolve well in certain types of water. Cosmogenous sediments come from asteroids or possibly comet remains.

THE CONTINENTS There are seven continents now, these are considered the major continuous landmasses around earth. These are permanent as far as we are concerned but were not very permanent in the past. You’ve studied 7 continents, but Europe and Asia are often combined to form Eurasia when it comes to geology. Australia is part of a larger region of islands collectively called Oceania, which includes the Pacific Islands. About 29 percent of the earth is covered with the continents. There is more continental earth above the equator than below it. Australia is confusing; it is a big island and a small continent, at least 4 times bigger than Greenland. Greenland is our largest island, part of North America. Continental crust is different from oceanic crust. It has more granite in it that contains a lot of aluminum silicate material. Oceanic crust is mostly basalt or hardened lava-like material. As mentioned, the continental crust is less dense overall and is older than the crust in the oceans. Expect the crust in the continents to be about 40 kilometers thick compared to only 6 kilometers thick in the ocean depths. The lithosphere is divided into plates that began much smaller. The continents are the older centers of these plates. Most plate boundaries are not near the edges of the continents themselves. The study of plate tectonics is how these plates move, shift, and subduct over time. All continents have flattened areas and mountainous ones. Shields are a major part of Africa but not as much as you'll find in Asia, which is more mountainous. Each continent has its own unique climate that affects everything else about it.

Cratons are the oldest nuclei or beginnings of each of the major continents. These areas are also called basement rocks dating from the Precambrian periods. There are actually numerous cratons that formed at nearly the same time. Look for them near the interior parts of continents and expect few earthquakes in these regions. Cratons have shields and platforms as part of them. Shields are exposed areas of ancient rock, such as you see in the Canadian Shield. Look for the oldest rocks here. There is also the Amazonian shield in South America, the Indian Shield and Angaran shields in Asia, the Baltic Shield in Europe, the African Shield in Africa, and one in Antarctica called the Antarctic Shield. Figure 8 shows Precambrian rocks on the Canadian shield:

Figure 8.

In North America, the Canadian shield is located along its eastern half to include Ontario, parts of Manitoba, Quebec, and just the extreme northern parts of the US central states of Minnesota and Michigan. While the shields are sloping in general, the platforms are the plains next to them. There is younger sedimentary rock overlying the

older basement rock. Some of this sediment occurred when the areas were covered with shallow seas millions of years ago. Mountain belts are also parts of most continents. These are narrow bands of mountains, such as you'll see in Andes and Rocky Mountain Ranges. These are areas where the crust has crumbled up and folded. Most are seen near plate boundaries and not in the middle of the continent. The mountains come when two plates slowly collide with one another. Larger mountains come where two areas of continental crust collide versus when continent collides with oceanic crust. The mountains around the world have different ages; some have eroded already, such as the Appalachians, while the Himalayans are still being built. Fractures can develop where crust falls into spaces that open up in the existing crust. You might see these called rift valleys, existing across any of the great shields. The Great Rift Valley in Kenya and similar rift valleys show some areas where there is upward movement of lava through the crust, forming flattened fields of lava. You can actually get eruptions in these areas as well. Figure 9 shows this Great Rift Valley:

Figure 9.

Volcanic Plateaus are flat basaltic rock areas where you'll actually see these vast lava flows in the middle of nowhere, such as the Deccan Traps of India and the Ethiopian Plateau located in Africa. Volcanic belts are narrow regions where there are a lot of volcanoes forming cone-shaped mountains like you might see near the edges of some continents or in island arcs in the ocean that form island chains. Mount St. Helens, Mount Fuji, Mount Hood, and Mount Rainier are all formations made from volcanoes rather than pushed up tectonic plates. Continents will extend below the surface of the ocean as well. Some continental margins are very large – hundreds of thousands of kilometers long and comprising 15 percent of the earth's ocean surface area. You can expect a few to exist 2 kilometers below the ocean surfaces. The continental shelf, the continental rise, and the continental slope are all parts of the continents. The official edge of a continent is then usually at the continental rise. The continents probably started as a chemical change in the earth's crust. Basalt from volcanoes is much denser than the crust of the continents. There were chemical changes that occurred to cause the crust to be of a structure with decreased density so it would float much higher on the mantle compared to oceanic crust. The continental crust started to be more stable around 4 billion years ago. Pieces of land accreted to other pieces. Accretion is just another term for sticking together of rocks. Africa itself was made from 5 separate cratons. Subduction zones are where the oceanic crust sinks below other rocky layers or plates. These are necessary because lava or magma comes up to make new ocean floor. The edges of the ocean floor must go somewhere to make room for the new floor. Ocean basins are young while the edges are older. Continental crust is too stable to be lost during subduction. Figure 10 shows a theoretical subduction zone in what you would call a convection current of magma and rock:

Figure 10.

Isostasy is a geologic term used to describe the fact that the lighter and bigger parts of the earth's crust rise, while the denser and thinner parts sink. Mountains are large partly because they erode from the top and not the bottom. This causes them to eventually become flat plains. Isostasy means that there is a balance between the upper weight of the continental crust and the lower weight beneath the earth's surface. When Pangaea finally broke up, it made Laurasia to the north and Gondwana to the south. Laurasia made most of the northern hemisphere, except the Arabian area and India. Gondwana formed the southern hemisphere continents. Gondwana fractured 94 million years ago, and Laurasia fractured 50 million years ago. We will talk more about continental drift in a later chapter. It was proven to be true by the fact that magnetic patterns frozen in rocks are different in orientation from other rocks. The magnetic parts of rocks are aligned at the time they were first solidified. In today's time, our current GPS systems can detect this drift.

KEY POINTS IN THIS CHAPTER •

The Precambrian era was long and started at the very origin of the earth.

•

All the spheres around earth affect each other.

•

Precambrian rocks are seen in the cratons where the continents were first formed.

•

The crust is a thin layer around the earth. This is where the lithosphere is.

•

The deeper mantle makes up the majority of the volume of the earth.

•

You should know about the way rock is formed and subducts along the various areas around the globe.

CHAPTER 2: QUESTIONS AND ANSWERS 1.

How old is the earth approximately? A. 2.7 billion years B. 3.8 billion years C. 4.5 billion years D. 5.9 billion years

What amount of earth's geological time was spent in the Precambrian era? A. 45 percent B. 62 percent C. 74 percent D. 88 percent

What lifeforms were the first to develop on earth? A. Bacteria B. Archaea C. Algae D. Plants

Where did most of the oxygen gas come from in our atmosphere? A. Comet activity B. Volcanic activity C. Photosynthetic activity D. Chemical activity

What word best describes a characteristic of the asthenosphere around the earth? A. Dense B. Gelatinous C. Crackly D. Liquid

What gemstone most resembles the stuff you'd find in the earth's mantle? A. Rubies B. Diamonds C. Garnets D. Peridots

Which process in the rock cycle happens primarily to magma? A. Metamorphism B. Weathering C. Sedimentation D. Crystallization

What part of the ocean floor is made less steep by sediment? A. Continental rise B. Abyssal plains C. Mid-ocean ridge D. Seamount

On what part of the continent would you find its official edges? A. Continental rise B. Rift valley C. Craton D. Volcanic Plateau

10.

What concept first proved the idea that continental drift was real? A. Examining the continental shields B. GPS satellite systems C. Magnetism in rocks D. It has not been proven

CHAPTER 3: GEOLOGIC TIME This chapter examines the concept of geologic time. This time dates back to the first days when the earth's crust was being developed. Older rocks look different from younger rocks; you need to know the difference between them. You will learn how to date rocks and how you can use rocks to indicate the age of fossils. The chapter also looks at the different types of fascinating fossils you can find in your own back yard, or nearby rock quarry.

KNOWN GEOLOGIC TIME PERIODS Geologic time periods are used to help organize our earth's history. This is a very long period of time to not have some way of breaking it up. When we break up geologic time, we use eras and periods to describe the different chunks of time. There are a lot of different divisions that are organized not by a specific length of time but are labeled according to the different things that happened to change the total climate and geological conditions on earth at the time. The different time increments are not the same. An eon is divided into eras, for example. Eras are divided into different periods. The order of time increment lengths from longest to shortest are: •

Eon

•

Era

•

Period

•

Epoch

•

Age

You will see how these things are divided up and why they have the names and features they do. Expect to see that there are usually some big changes happening to cause a change in the name of any time increment. The system we use now is different from 42

what it used to be and is still evolving over time. You will learn a lot just by studying the different periods, although these are usually broken up further into epochs. Figure 11 shows these in better detail:

Figure 11.

PROTEROZOIC ERA The Proterozoic era is important in geologic time. There was a lot that happened in this era, extending from 2.5 billion to 541 million years back in time. The tectonic plates rested or floated on magma, but the magma then is different than now. The plates were not as thick as they are now, and the magma was both hotter and more liquid. This

meant that the continents were moving a great deal faster and further than you see them. There was a single continent then, which was Rodinia. Laurentia, the early part of North America, was in the middle of this continent, next to the cratons used to make Antarctica and Australia on the West and next to Africa on the east. The early life was anaerobic – did not use oxygen – mostly because oxygen was unavailable to them and it would have been deadly anyway. These would have later been crowded out by the archaea organisms, which were photosynthetic. Eukaryotes soon followed. These organisms were like us in that they had nuclei and clusters of chromosomes instead of just one circular strand of DNA; mostly, however, these were single-celled organisms or at least very simple in the beginning. Many of these organisms used oxygen, while a few were photosynthetic. The end of this eon marked the time when a few multi-celled eukaryotic organisms existed. Multi-cellularity was important for the progression of life. You could only get so far with single-celled organisms as far as real life-forms on earth were concerned. Prokaryotes like bacteria are not capable of doing much; they are too simple and cannot form multicellular organisms. They also have genetic linkages from mother to daughter that are very different from ours. Eukaryotes can use sexual reproduction, allowing for more diversity in the subsequent generations. The end of the Proterozoic eon was marked by the coming of what we call Snowball Earth because the earth was almost completely frozen. This was also called the Cryogenic time. It may have come because oxygen replaced the greenhouse gases, cooling the atmosphere dramatically. It also happened because the sun wasn't as strong as it is now, and ice itself is so reflective it would have limited the warmth of the earth, leading to a feedback effect. Once it reached a critical level, the ice would have just made more ice. The end of snowball earth was called the Ediacaran period after the many fossils showing multicellular organisms coming from hills of the same name in Australia. Others from this time period have been found all over the world —all dating from about 600 million years ago. The fossils found from this time are not like any living thing we now know about. These are all Precambrian fossils.

THE PALEOZOIC ERA This era happened over a 290-million-year time period and started with what's called the Cambrian Explosion. This was when the amount and diversity of life on earth really exploded. It ended with the Permian extinction, which likely destroyed most of those life-forms for all eternity. This era had six distinct periods that we know of currently. There were two types of bacteria living in the millions of years before this eon began. Some were called heterotrophs, which survived on other living things —mostly other bacteria. Others were called autotrophs —they did not need other living things but relied on the sun's energy to get their energy. Autotrophs were so important because they used photosynthesis and made oxygen as a toxic byproduct. At one point, a smaller bacteria must have been eaten by a larger one. The smaller one produced energy and became symbiotic enough to become the energy factories in eukaryotic cells we now call mitochondria. These are all part of nearly every eukaryotic life form and cell today. As cells became more specialized, they formed multicellular organisms that were probably initially tube-shaped water dwellers without any mobility. The Cambrian explosion meant that many new species were formed. Most phyla that existed during that time have since become extinct. You would have seen a lot of arthropods like trilobites, mollusks, brachiopods, and others. You have probably seen many brachiopod fossils, even if you haven't known it. Figure 12 shows a brachiopod fossil:

Figure 12.

You can see brachiopod fossils everywhere, even in a parking lot where you can find tan or gray rocks that have these fan-shaped creatures imbedded as fossils within them. There were a number of periods in this Paleozoic era. These were the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Rather than remember these, you should know that the earliest fossils were in this order: mollusks, brachiopods, trilobites, crinoids, and then fish. The crinoids were interesting because their fossils look a lot like flowers. These were animals that were the ancestors of the sea urchins, sea cucumbers, and starfish you see today. Figure 13 shows a typical crinoid fossil:

Figure 13.

Notice that most of these were not widely mobile in any substantial way. Their main goals were to eat, consume oxygen, reproduce, and move around their general area. This was when the main supercontinent was called Gondwana. It was closest to the South Pole. North America was not even part of the continent at that time. There was a small area where the North American continent could be found nearer to the equator. Most life was not initially on land in the beginning of this era. The Silurian period was from about 419 to 443 million years ago. This was when land animals and plants could be found. There were still few significant plants or animals until the Carboniferous period at the end, when giant forests could be seen everywhere. Imagine so many plants that the oxygen level on earth was 14 percent higher than it is now.

What about insects? Yes, there were many insects during this time – and they were huge! Dragonflies and centipedes reached sizes that were nearly 5-7 meters in total length or wingspan. Four-legged animals are called tetrapods. These were possibly able to live on land because of the high oxygen levels in the atmosphere. They were mainly amphibians, but much larger than you would see today. The Paleozoic era came to a screeching halt with the Permian-Triassic mass extinction event. It was far worse than the one that killed the dinosaurs, destroying about 95 percent of all species living at the time. No one knows why it occurred; the theories will be laid out next. This began the Mesozoic era.

THE MESOZOIC ERA The Permian-Triassic extinction was rough on this planet. The causes were probably multifactorial. There was more carbon dioxide in the air due to burning after a giant eruption in the Siberian Traps region. The oceans then became too acidified and lacked oxygen to support life. This led to a 3-level series of extinctions over a brief time in geologic time, that is – the entire time period happened about 252 million years ago. The Mesozoic era started with Europe and Asia colliding with North America. These continents formed a giant supercontinent we now called Pangea. The climate was warmer then, and most areas on earth were tropical by today's standards. The seas were much lower, allowing for more land mass. A few areas were dryer and were desert-like. This era had three periods —the Triassic, the Jurassic, and the Cretaceous. Life needed a great deal of recovery time after the mass extinction events prior to this era. Plants made it through the extinction more than the animals did but there were wide temperature variations they needed to get through after the event. Ferns and plants called gymnosperms were able to spread through the air to allow for different reproductive methods and wider spread of these plants. Spore-forming plants were better able to get through droughts. Corals, fish, and mollusks were widespread in the ocean. Reptiles were able to be on land and water to catch predators better. Mosasaurs and Plesiosaurs were the first of what we now call dinosaurs. Near the end of the Permian period, were animals called 48

synapsids. These were mammal-like that became extinct as this period ended. The animals that entered the Mesozoic era needed to adapt to changing temperatures. Reptiles were good at this, so they thrived. The first of these reptiles were called diapsids because they had two separate holes on either side of their skulls just behind their eyes. The dinosaurs came after and were also diapsids. The Jurassic Period and Cretaceous Period near the end of this era were mainly the dinosaurs. Plants were also very gigantic. There were a few small mammals but they did not dominate the land like the dinosaurs had. There was another mass extinction to end the Cretaceous period. The dinosaurs died off at this time, even though it wasn't as large an extinction event as the Permian-Triassic extinction. An asteroid impact likely caused this mass extinction.

THE CENOZOIC ERA The Cenozoic era marked the end of what we call the geologic eras. This was when mammals finally made their mark as being dominant. All of the major species evolved continuously as well during this time. Mammals survived the extinction that killed the dinosaurs, possibly because they didn't have as many needs for the scarce resources of the time. None were as big as the dinosaurs but a few were much larger than today's counterparts. The mammoths are well-known for being large but so were smaller mammals like beavers, which were more than 4 times larger than they are today. The continents had separated by this time to where they now are, except for Africa, South America, and India. These were too far south and moved northward to where they collided with the northern continents. The Alps and the Himalayas were created at this time; the Himalayas are still being built. The climate has become generally cooler since the beginning of the Cenozoic era. The overall landscape on earth has also become drier with more grasslands for grazing animals to better survive. There are not a lot of fossils from this time as it is too recent for this to have happened and is still part of the time we are in. It began 66 million years ago — a drop in the bucket when you consider the expanse of all geologic time. It has

been divided into the Paleogene period, the Neogene period, and the present Quaternary period.

DATING ROCKS All rocks look the same at first, but many in the same pile of random rocks you might find have come from vastly different time periods on the geologic scale. A lot has happened in these few billion years since the earth was formed. It would be nice to see how to tell when in time a rock was first develop. Fossils can help with this in some cases. You would need to know what the fossil is first and then find some relative way of seeing when the fossilized organism first died and became trapped in substances that later become rocks themselves. If you know when the organism died, you can see what else was laid down at the same time and possibly their relationships back in time. There are three major approaches to dating materials in geology. You can do relative dating once you know the exact date of at least some of the species in the rock. Think of sediment as it is laid down over a long period in time. What is the sediment? How long did the sediment take to get as thick as it is in the rock? What is the date of any known fossil in that sediment? What about the dates of other things above and below this level? The second approach involves actually dating the materials in the rock to a known date in time. This isn't always exact and the degree of exactness depends on your dating method. Carbon dating, for example, is only reliable for dating things from within the last 50,000 years and is most accurate when combined with tree-ring dating. The third approach involves magnetism. The magnetic field direction and location has changed, as you know. This helps determine many things with regard to the dating of rocks, just as it proved the theories on plate tectonics. Relative dating works best for sedimentary rock but it can be used for volcanic rock from volcanoes erupting more than once. Each layer or stratum is generally laid down horizontally. Exposed sedimentary rock is seen along the Grand Canyon or possibly in

your own back yard. Figure 14 shows strata near a river that was once much wider. This rock face was once sediment at the bottom of a wide ancient river:

Figure 14.

The study of strata like these is called stratigraphy. You should recognize that the older layers are deposited first and that they are at the bottom of any exposed rock face. If you see major changes in a strata's appearance or horizontal tendency, something is off, you can assume that something happened after the strata were laid down. The three main rules of stratigraphy are called: 1. The Principle of Horizontality —layers are laid down in a near horizontal way initially 2. The Principle of Superposition —the top layers are generally younger 3. The Principle of Cross-cutting relationships —the layer that crosses other layers must have formed after the older strata have solidified into rock. 51

A cross-cutting layer would be one that extends across others, it is the youngest layer by definition. It happens if there are layers that are solid but then get fractured enough for another layer of sediment to slip into the cracks. This crack will be diagonal to the other layers and will cut across the others. This only works if the other layers they cut through have become rocks first. A series of strata that are no longer horizonal on a rock face usually means they have gotten thrust upward or downward in some way. This is another way of determining what happened to any given area of land where you can see the layers of rock exposed. You can add a fourth principle to fossilized rocks. This is the principle of faunal succession. It means that the various fossil species will appear and disappear in the same order. Once you have extinction of a given species, it will not be seen within younger rocks. You can get a time zone when known species existed and overlap them with another species to find a range at which the second fossil must have been laid down and when the species lived. Some species lived for a long range in time, while others a shorter range. Knowing these ranges helps you narrow down the range of a species you are wondering about. Index fossils are those most used in dating fossilized specimens. They are great for dating because they did not exist in living form for a long period of time. Ideally, they should be widespread and easy to identify in their fossilized form. Primate fossils are not good as index fossils because they are so rare, even if they existed over a short time span. Other mammals (like pigs or rats) are better as index fossils because they are common and evolved more quickly over time compared to primates. Numeric aging of rocks attempts to get an accurate date out of the rock in question. Radiometric dating is commonly used for this. This involves using isotopes of the same atom. Atoms exist in their common form, usually with the same number of protons and neutrons in the atom's nucleus. Carbon-12 has 6 protons and six neutrons. Isotopes of carbon are still made of carbon atoms but will differ in atomic weight. This is because neutrons weigh the same as protons and add weight but little else to the atom. Carbon14 has 2 extra neutrons per atom.

Carbon-14 isn't as stable as carbon-12. It will decay in ways that are not random but happen at a steady pace to make carbon-14 to become carbon-12. This is called the decaying of carbon-14. This is similar to radioactivity but in very slow motion compared to uranium, for example. It also involves changes in the neutron number and not the numbers of negatively charged electrons. Potassium does the same thing by turning a heavier isotope into a lighter one. Radioactive decay takes a parent isotope and turns it into a daughter isotope that is more stable. The time it takes for half of an amount of a given substance to do this is called the half-life. You use the known decay rate and the amount of each substance (parent versus daughter isotope, for example) to see the exact date. There are other methods used in absolute dating of rocks, such as thermoluminescence and electron spin resonance. These look at how radioactivity in a rock has affected the crystal structure of crystals in the rock. This is a summary of the techniques used in dating rocks: •

Radiocarbon —it has limited usefulness because you need relatively recent material that has carbon in it to a great degree, such as charcoal, seashells, bones, or wooden materials. Based on the idea that the carbon atoms made don't decay until the substances have left the biosphere.

•

Potassium-argon dating —this can extend to billions of years in the past and relies on the decay of potassium found in certain rocks that have potassium in them.

•

Uranium-lead dating —this is based on the decay of uranium into lead and can work for items from 10,000 to billions of years ago.

•

Uranium-series dating —this is based on the decay of uranium into thorium and is used for things like calcium carbonate, seashells, teeth, coral, and minerals with uranium in them. It would work for things dating billions of years ago.

•

Fission track dating —this is used for substances from 1000 to up to billions of years ago in the past. It relies on uranium decay and measures the tracks of damage in glass and minerals affected by uranium decay.

•

Thermoluminescence —this is good for things up to a million years ago and is used to date stone tools, pottery items, quartz, or feldspar. It works for items less damaged by the sun's rays or heat because they were buried and protected at some point in the past. It is also based on the trapping of electrons in mineral crystals.

•

Electron spin dating —this works for things exposed to uranium and looks at mineral lattices affected by this radiation. It dates things up to 3 million years ago.

•

Cosmogenic nuclides dating —this helps dates olivine or quartz coming from volcanoes and is based on the decay of substances by cosmic rays. It works for items up to 5 million years ago.

•

Magneto-stratigraphy — this works for potentially billions of years in the past and looks at the layers of rock and their relative magnetic spin. It would work for volcanic rock and sedimentary rocks.

•

Tephrochronology —this is a method that works for items that are at least 100 years old but also as far in the past as billions of years. It dates things ejected from volcanoes to link things found in distant successions of strata.

Radiation is decay but generally involves the decay of the electrons in an atom, turning these electrons into tiny missiles that get trapped into imperfections within crystals. The techniques of optical stimulating luminescence, thermoluminescence, and electron spin resonance all measure how these imperfections trap runaway electrons. Traps eventually get saturated and aren't able to trap more; this means that rocks older than 100,000 years old are less likely to be dated easily using this method. Magneto-stratigraphy is helpful now that we know times when the earth has reversed polarity. This is measuring rocks laid down over geologic time and other dating methods to create a polarity signature. This geomagnetic polarity time scale is not equal so you get a barcode of sorts showing different strata having their own magnetic pole strength and direction. As you can imagine, you would have needed to have other corroborating dating methods the first time this barcode or scale was generated.

FOSSILS AND FOSSIL TYPES Fossils take some experience in identification of them. The easy-to-see fossil as a perfect specimen does not show up every time you see a rock; in fact, these are rare. There is more than one type of fossil you might encounter. Here are some examples: Body fossil —this is a fossil you get with the entire organism trapped in amber, which is fossilized tree sap. Bones and teeth last longer in any fossil, including these, but body fossils trap the entire insect or other small creature. Figure 15 is what this looks like:

Figure 15.

Molded fossils —these are also called casts. This is the imprint of a shell or bone on a harder rock that then gets layers of sediment dumped on it. A shell might have an internal mold or external mold, depending on how it is laid out. Internal molds are seen when the inside of the shell is seen, while an external mold is when you see the bone or shell as it looked like on the outside. Casts are seen when molds fill with sediment.

Petrified fossils are those that have rock materials like silica and calcite fill in where the organism's remains once were, making a perfect example of the item but in mineralized form. This process, called permineralization, happens to things like trees. Figure 16 is a good example of a petrified animal:

Figure 16.

Footprints and trackway fossils —these are also called trace fossils because they just show how the animal lived and moved, but not the animals themselves. You might see footprints or evidence of a tail dragging.

Fossilized feces —these can say a lot about what any animal may have eaten. These are also called coprolites. Because feces tend to decay, these are very uncommon among fossils. You might find bones, shells, or teeth in them, among other things. Carbon films —these are thin layers of carbon you'll see when you have an animal or plant that leaves nothing but its carbon footprint. Delicate ferns often leave nothing behind except this kind of carbon staining pattern. Pseudo fossils —these are simply the track of water and minerals dissolved in them through other sediments. They look like plant or animal parts but are instead just the appearance of them.

KEY POINTS IN THIS CHAPTER •

Geologic time was long, divided into eons, eras, periods, epochs, and more.

•

Most eras were marked by a large change in the earth's climate and major species on earth.

•

The first common fossils were of things like mollusks, brachiopods, and arthropods but very early fossils found on earth were of algae.

•

The transition from anaerobic to aerobic organisms happened when oxygen was produced in large numbers by photosynthetic organisms.

•

The Permian-Triassic extinction happened when the oceans acidified with dissolved carbon dioxide emitted by large volcanoes in Siberia.

•

Carbon dating is not used much in rock dating but there are many other dating features used for this process. Most are based on uranium decay or Potassium decay over time or the effects of radioactive decay in crystals.

•

Stratigraphy involves several principles that help to relatively date fossils and other aspects of rock.

•

There are different kinds of fossils in rock that will say something about living things from along ago.

CHAPTER 3: QUESTIONS AND ANSWERS 1.

Which time increment in geologic time is the longest? A. Epoch B. Period C. Eon D. Era

The time we call the Proterozoic time was important for the first multicellular organisms of any kind on earth. Was this time called an epoch, period, eon, or era? A. Epoch B. Period C. Eon D. Era

Which fossil from the Paleozoic era looks a lot like a fan or flower on a stalk? A. Crinoids B. Trilobites C. Mollusks D. Brachiopods

What ended the Paleozoic era, giving rise to the Mesozoic era? A. A glacial period B. Snowball earth C. Rise of the dinosaurs D. Permian extinction

Which era came last among the geologic eras? A. Mesozoic B. Cenozoic C. Proterozoic D. Paleozoic 59

What geologic period are we currently living in? A. Paleogene B. Neogene C. Quaternary D. Tertiary

Radiometric dating uses atomic isotopes that are elements with atoms differing from each other in what way? A. Their atomic number B. Their formal charge C. Their atomic weight D. Their atomic age

Which dating method for rocks is not usually considered to involve absolute dating? A. Magneto-stratigraphy B. Potassium-argon dating C. Thermoluminescence dating D. Stratigraphy

What type of fossil is also called a coprolite? A. Trace fossil B. Body fossil C. Carbon film D. Feces fossil

10.

A fossil that shows how an animal lived and less what it looked like is probably what? A. Carbon film B. Trace fossil C. Mold fossil D. Body fossil

CHAPTER 4: PLATE TECTONICS This chapter is a discussion of what we know about plate tectonics. It is still called "plate tectonic theory" even though there aren't any legitimate counter-theories on why the continents exist at all and where they are located. What plate tectonics means for geologists is that the earth is still changing and phenomena like earthquakes and mountain-building can be easily explained by understanding how the lithosphere moves on this planet.

THEORIES OF PLATE TECTONICS FROM THE BEGINNING Alfred Wegener opened the discussion of plate tectonics in 1912 when he first wrote about continental drift. The initial idea was that the continents were once one giant supercontinent called Pangea; it drifted apart to make the current continents. We have since learned that there were supercontinents before Pangea. It was thought initially that the continents were like icebergs that basically drifted on something denser than rock. Even though rock is heavy, it is not as dense as magma, which is liquid rock. Any third grader will tell you that the eastern section of South America greatly resembles the western part of Africa. They seem to match like two pieces of a jigsaw puzzled. Wegener noticed this and others found that fossils from certain plants and ancient animals are found in all of the major continents, except for Europe, Asia, and North America. In 1937, Alex du Toit wrote a publication that illustrated the concept of wandering continents by showing evidence for Gondwana, which was almost entirely in the Southern Hemisphere. Despite of all this detailed evidence, many scientists still did not accept the idea that the continents could literally move around. They were just so big and wieldy to move, many thought. Gradually, however, the theory that became plate tectonic theory gradually took hold. Scientists began to think that convection currents beneath the earth's

lithosphere or crust may be driving this continental drift phenomenon. Plate tectonics came forth to emphasize the stability of the continents along with their mobility. Paleomagnetic experiments furthered the idea of continental drift and the movement of our lithosphere. Rocks will maintain their magnetic field direction only after they have solidified. It was first thought that the pole wandered and not the continents. By the 1950s, however, this was sufficiently disputed. The continents were clearly drifting and not the poles. Another piece of the puzzle fell into place when researchers from the 1950s and 60s studied the ocean floor —specifically the bathymetry or the depth of the ocean floor. They noticed that the ocean floor appeared to be spreading. These two corroborating facts were combined to make many scientists hooked on the idea that plate tectonics was a real phenomenon. Imaging techniques have since shone light on the fact that there were trenches between the two continents and that these were areas that represented sea floor spreading. Seismic imaging showed that the earth's crust could disappear in some places into the mantle. This was how the earth could balance the addition of the earth's crust in other places. Another interesting finding had to do with plumb line deflection at the top of the Andes mountains. Based on these findings it was felt that mountains were less dense but that they projected downward into a much denser layer beneath them. This gave rise to the idea that mountains must have roots. Earthquakes, too, are clustered in certain areas. These were around spreading ocean floor areas and oceanic trenches. These seismically active areas were found to be angled and to extend hundreds of kilometers into the earth itself. These were since called Benioff zones. These zones were mapped out precisely in the 1960s. The mid-oceanic areas consist mainly of a floor of basalt, which is new rock that comes from solidified lava. Researchers discovered this in 1947; they also determined that there was a ridge in the deepest parts of the ocean called the mid-oceanic ridge. There is no granite in these areas at all, while there is a lot in the mid-continental regions. Bathymetry was used to determine that these mid-oceanic ridges existed. 62

It wasn't until the mid-1960s that the ideas of new floor being built in some places, and old floor being extracted or subducted into the earth were finally put together to explain why the earth wasn't expanding or shrinking. Magnetic studies of the ocean floor added to the puzzle solution by showing striped patterns of polarity in one direction and then polarity in the opposite direction. This occurred as new floor was made along the mid-oceanic ridges over millions of years when the earth had one polarity or another. This provided a zebra-like situation with stripes wider in places where the polarity in one direction lasted longer in time. The mid-oceanic ridges act like a conveyor belt, spitting out the floor in a linear fashion along the ridge to either side of the ridge.

PLATE TECTONIC BASICS There are currently seven accepted major plates and many minor plates. The major plates are the African, North American, Eurasian, South American, Pacific, Australian, and Antarctic plates. They are not moving at the same rate or direction. Some are moving about 10 centimeters a year, while others move at just 2 centimeters per year. The determination of what is a major, minor, or micro-plate is largely arbitrary. A major plate is defined as one that is 20 million square kilometers in area. The major plates and their location now can be seen in figure 17:

Figure 17.

The largest of the major plates is the Pacific plate at more than 100 million square kilometers. In descending order after this are the North American, Eurasian, African, Antarctic, Australian, and South American plates. The Indian plate is a minor plate with major consequences. It is the one that is participating in creating the Himalayan mountains. Minor plates besides the Indian plate are the Somali plate, the Amurian plate in East Asia, The Sunda plate in Southeast Asia, the Philippine Sea plate, and the Nazca plate in the Eastern Pacific Ocean area. The areas where the plates bump into one another are extremely prone to earthquakes. Seismographs are able to see where the epicenter of an earthquake is; these are largely around the plate edges. They also are seen in the areas of the mid-ocean ridge plates.

HOW DO THE PLATES MOVE? The plates move around on the earth's surface due to the convection currents in the magma beneath them. Convection is essentially flow of liquid that start as hot magma at the mid-oceanic ridges and ends in subduction in the deep sea trenches. This happens in all the earth's major oceans in ways that act like a conveyor belt driving the magma into circular patterns all over the world.

PLATE BOUNDARIES

Figure 18.

The plate boundaries or "edges" do different things depending on what's happening with its neighboring boundary. Take a look at figure 18 here: These are the main boundary types you might see: •

Divergent boundary – you can also call this a constructive boundary. It is seen where new magma is being formed. Seafloor spreading happens at divergent boundaries. You will see ridges form at the area of spreading. The area of the plate increases here and small underwater volcanoes can form. Shallow earthquakes might also be seen in this region but they don't affect much at these locations. There is one each in the Atlantic and Pacific oceans as well as in the East African Rift, East African Valley, and the Red Sea. The East African Rift Valley is separating the Somali plate from the African or Nubian plate. The Red Sea literally parts where the African and Arabian plates are separated.

•

Convergent Boundaries – These are destructive boundaries or active zones where the plates are crashing together. There can be subduction happening or a true collision with mountain-building. The Andes Mountains, Sierra Nevada, Balkan, Cascadia Mountains, and others have happened due to subduction plus convergence of plates. Earthquakes can be seen here as the denser oceanic parts subduct downward, releasing gases like water vapor from minerals that have water in them. Volcanoes also form in these regions and you'll see volcanic island formation. If continents crash into continents without subduction, you will see taller mountains, such as the Himalayas and the Alps.

•

Transform Boundaries – these are also called conservative boundaries. These are where plates slide past one another or grind along fault lines. There is usually a left side or sinistral side and a right side or dextral side (based on the observer). There is a spreading center in this region and many earthquakes. The San Andreas Fault is a transform boundary with dextral motion. Anywhere you stand along this fault, the part near the Pacific Ocean is traveling northward with respect to the rest of the United States.

EXAMPLES OF THESE PHENOMENA IN GEOLOGY These are some of the more commonly known geological occurrences and how they are explained by understanding plate tectonics: •

Mid-oceanic earthquakes and tsunamis – these happen along the mid-oceanic ridges as the magma and crust are shaken in the process. These are deep ocean earthquakes that can disrupt the ocean enough to create giant tsunamis.

•

Continental arcs – these are lines of volcanoes on the edges of continents made by the combination of convergence and subduction. There are often both earthquakes and volcanoes here. The Juan de Fuca plate in the Pacific Northwest is a tiny underwater plate subducting under the North American plate. This has led to the formation of Mount Shasta, the Medicine Lake Volcano, Mount St. Helens, and the Lassen Peak volcanoes in the Cascade Mountains.

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Island Arcs and Ocean trenches – these happen where an oceanic plate subducts underneath another oceanic plate. You will get the upper plate pushing up to make an arc of islands. The Aleutian Islands were made this way. Figure 19 shows this type of situation:

Figure 19.

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Large mountain ranges – these are continent to continent convergences. There is never any subduction here because the crust is not dense enough. Expect metamorphic rocks here because of the pressure involved. There are no volcanoes in these regions because the crust is too thick. Large earthquakes are probable. The Appalachians are leftover mountains from when North America crashed into Eurasia.

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Massive Earthquakes – most of the massive earthquakes on earth are created by transform boundaries on continents. This explains why the worst earthquakes in North America occur in places like the San Andreas Faultline.

MEASURING PLATE MOTION It is estimated that a supercontinent like Pangea gets made and then breaks up every 500 million years. We can measure the movement of the plates to get an idea of where they are heading. This measuring system is called geodetic plate motion detection or geodesy. GPS systems above the earth are very stable and can detect the earth's

movement. The data is becoming increasingly accurate over time due to the satellites in space. Geodesy has determined that there is plate movement within plates. The Tibetan Plateau region and the mountains in the American West are all places where there are intracontinental movements within the plates themselves. Several microplates have been found using GPS. Present movement of the plates can be detected using seismic, geometric, and paleomagnetic concepts. Paleomagnetic concepts are those recently discussed, where the ocean floor can be seen as having zebra stripes various magnetic reversals. Magnetometers used initially to detect submarines can find these signatures from the air. The last reversal was about 780,000 years ago. Geometric methodology can give us an idea of the spreading direction of the earth's crust by looking at transform faults in the ocean. You'll see treads on a spreading ridge that show the direction of the spread. Once you know the speed and direction of the spreading areas, you can determine that these match with the known GPS measurements we currently know about. Seismology can also look at the orientation of the different fault lines around the earth to help in parts of the world less easily mapped in other ways.

KEY POINTS IN THIS CHAPTER •

Plate tectonics was proposed by Alfred Wegener, a meteorologist who was the first to notice the similarities between the western edge of Africa and the eastern edge of South America.

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The plates represent crustal areas that migrate or float on magma. Convection currents cause the magma to rise and fall in various places.

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A major plate is greater than 40 million square kilometers in area. The largest plate is the Pacific. There are numerous minor and micro plates.

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Plates come together or separate. These are called convergent and divergent boundaries, respectively.

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Convergence can happen with or without subduction or sinking of half of the boundary beneath another. The sinking half is denser and is often the oceanic half if ocean and continental regions are coming together.

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Convergence without subduction usually creates giant mountain ranges in the middle of a continent.

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Divergence can happen in oceanic situations or on land. In both areas of the world, it gives rise to rift valleys where magma comes up from beneath thinner crust.

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In transform boundaries, plate edges are slipping past each other. Here is where you will get a great many earthquakes as the shift is dextral or sinistral in nature.

CHAPTER 4: QUESTIONS AND ANSWERS 1.

What was the first evidence that plate tectonics might be real? A. The outlines of Africa and South America were seen as similar. B. The mountains were found to be rising. C. The sea level was rising. D. Animals all over the earth were found to have a common ancestor.

What does plate tectonics mean for earthquakes? A. That they can occur anywhere on earth B. That they only occur over the ocean C. That they generally occur along plate edges D. That they occur mainly in warmer weather

What is about the fastest rate that a tectonic plate will move per year? A. 2 millimeters B. 1 centimeter C. 10 centimeters D. 1 meter

Which tectonic plate around earth was the largest? A. Pacific B. African C. Eurasian D. Antarctic

What phenomenon most creates the movement of the plates on earth? A. Crystallization B. Precipitation C. Gravity D. Convection

What is not true of a divergent boundary in plate tectonics? A. They are only seen on the ocean floor B. They are seen on both land and on the ocean floor C. They are called constructive boundaries D. Continents between plates are moving further apart on these boundaries.

Which most dictates whether a mountain is built by subduction and convergence together? A. The mountains are made from granite B. The mountains must have a volcano as part of it C. The mountains must be in the middle of the continent D. The mountains must be near the edges of a continental area

What plate tectonics phenomena cause a continental arc to occur? A. Divergence with subduction B. Convergence without subduction C. Convergence with subduction D. Transform boundary movement

What would least likely be seen in a continent to continent convergent region? A. Metamorphic rock B. Earthquakes C. Mountains D. Volcanoes

10.

GPS is used in plate tectonics. What major geologic phenomenon was uncovered this way? A. Intra-plate crustal movement B. Magma temperature C. Volcano formation D. Sub-oceanic subduction zones

CHAPTER 5: MINERALS IN DETAIL This chapter begins to talk about what many people think geology is all about – cool rocks and minerals. A mineral is a hardened substance from the earth that is made from a single element or just a few elements in a compound. The two main mineral classifications are the silicates and non-silicates. You will learn how to classify and identify the most common minerals you'll find around the world and even in your own backyard.

WHAT IS A MINERAL IN GEOLOGY? There are many known minerals in geology. People love to put them in jewelry or in pieces of art. What really is a mineral from a geological perspective? A mineral is what all of the earth's rock and sand are made from in varying degrees. To be a pure mineral, it must be a homogeneous substance made from a single element or a compound made from several elements. Any given rock you pick up can be made from several minerals at the same time. There are five main characteristics or traits of any mineral. These include the following: 1. A mineral must be naturally-occurring, which means that steel is not a mineral. 2. A mineral must be inorganic – not made from plants or bone, for example. 3. A mineral must be solid at room temperature in its most stable form. 4. A mineral must have an orderly internal structure that is geometric. This means that it must be crystalline. On the other hand, not all crystals are minerals because organic crystals don't count. 5. There must be a specific chemical composition that is basically the same everywhere on earth.

Many minerals are considered gemstones – cut and used to make jewelry. Not all gemstones are minerals, however. Amber and coral are living things used in jewelry but not at all considered minerals. There are two different basic classifications of minerals. These are silicate and nonsilicate minerals. Silicates are extremely common and have some type of silicone tetroxide (SiO4) in them. Silicon is one of the more common elements in the earth's crust. The most common is oxygen by far but silicon is the second-most common element in the earth's crust. For completeness, you should familiarize yourself with the most abundant elements of the crust by weight. Oxygen makes up 46 percent, followed by silicon, aluminum, calcium, iron, magnesium, sodium, and potassium in order of abundance. Non-silicate minerals are any that are not made from any silicon. There are characteristics of minerals we will talk more about soon. These include color, ability to be cleaved, hardness, luster or shininess, specific gravity or density, and streak, which is whatever color the rock makes when scratched against a white tile or similar surface. The common minerals you should be able to identify include these: •

Quartz – this is a common silicon-based mineral, made from silicon dioxide. There are several colors you might notice, including rose quartz, citrine, which is yellow to green in color, amethyst, which is purple, and smoky gray quartz. You will see this mineral in all types of igneous, sedimentary, and metamorphic rock.

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Potassium feldspar – this is made from a silicate that also has a lot of potassium in it. Because of the potassium, it is pink to salmon in color. It is not as hard as quartz and has what's called a perthitic texture due to its streaky but stubbylooking prisms. Figure 20 shows this type of rock:

Figure 20.

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Plagioclase feldspar – this is a silicate with either sodium or calcium in it. There are stubby prisms like potassium feldspar but are white or gray and not pink. There will be a glass-like luster to these rocks. These can be found in either igneous or metamorphic rocks.

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Mica – this is a group of similar minerals made from silicates but also containing iron, magnesium, potassium, silicon, aluminum, and some water. You will see these as having flat, bright crystals that peel off in smooth flakes. Mica is very soft and will scratch off easily. It can come in several different colors. The two main kinds are biotite and muscovite. Figure 21 shows mica flakes imbedded in quartz:

Figure 21.

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Amphiboles – amphiboles are also silicate minerals that look prism-like with long thin crystals. Most have calcium, aluminum, or iron in them. These elements make them dark. One of the more common amphiboles is called hornblende. It is dark green or blackish in color; they are seen in both igneous and metamorphic rock. Figure 22 shows this type of mineral:

Figure 22.

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Olivine – this is a silicate mineral that contains both magnesium and iron. It is green and glassy – often seen in basalt or in rocks formed only at high temperatures. It becomes peridot as a gem. A dunite is a rock made from pure olivine.

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Calcite – this is essentially calcium carbonate that may be clear or white. It is soft enough to be scratched with a knife. It will cause effervescence contact with hydrochloric acid. This is the same stuff that seashells are made of.

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Talc – this is the softest mineral you'll find. Scratch it with your fingernail and you'll see that it is friable for a rock. It contains magnesium and is a silicate. It feels greasy and looks pearlescent. It is seen with metamorphic rocks when other rock types get deformed.

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Fluorite – Fluorite is a crystal made of calcium fluoride. It is extremely colorful in ranges of colors like yellow, blue, green, and purple. You can easily detect it

under UV light sources. It isn't as hard as quartz, even though it looks a lot like it.

HOW MINERALS FORM You need certain criteria to make a crystal big enough to see. The elements must first be present in sufficient quantities and the right proportions. The physical conditions must also be right for these elements to combine in the right way. They also need to be left undisturbed long enough to grow into their crystalline shape. The existing temperature, level of oxygenation in the environment, pressure, water availability, and pH all determine how a crystalline mineral grows. Time matters because it makes for bigger crystals without something to disrupt the process. Most minerals were floating around as part of the liquidy magma deep inside the earth. As magma rose and cooled, the minerals within it also cooled and solidified. Rapid cooling means you'll get smaller crystals, while slow cooling has the opposite effect. Besides cooling in magma, minerals can form in these other ways: •

The chemical compound can be dissolved in hot water and will crystallize during evaporation or cooling of the water.

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The mineral can precipitate out of a hot gas, such as you'll see emitted from volcanic vents.

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Pressure alone can form a mineral during metamorphosis.

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Exposure to weathering and air can create an oxide mineral.

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Organisms can contribute substrate for a mineral, such as seashell material or calcium carbonate. Teeth and bones also form apatite crystals that can contribute to mineral formation.

Rocks are essentially collections of minerals. Magma is basically melted rock that can exceed 1000 degrees Celsius. It cools as it makes contact with air, water, or the earth's surface. Minerals can become very large, depending on the circumstances. Granite forms from hot magma that has slowly cooled. The main minerals in granite are: 78

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quartz

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potassium feldspar —which is pink

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biotite— which is black

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plagioclase feldspar —which is whiter than quartz.

Figure 23 shows granite up close so you can see these features:

Figure 23.

Lava is just magma that has reached the surface of the earth. It cools very rapidly due to our surface temperatures, meaning the crystals inside them just don't grow big. Its chemical composition is the same but the crystals would be extremely small – below the level of microscopic. Minerals can begin in aqueous solutions. Oceans are great places for solutions of any kind. As the water reaches inland or evaporates, the minerals will crystallize. Some will precipitate early because they aren't very soluble in water in the first place. Halite and

calcite both precipitate out of water easily. Halite is just sodium chloride —table salt. Look for lots of this in the Great Salt Lake in Utah. Tufa towers are calcium-rich stone formations made when spring water rich in this element bubbles into an alkaline pH lake environment. As the lake level drops, towers form. Figure 24 shows these towers:

Figure 24.

Hot underground water picks up dissolved particles in exiting rocks. The water can flow and cool, depositing some of these minerals into the cracks in these rocks. When you see interesting veins in a darker rock, this is from water that has seeped in and left behind crystalline minerals. You can also get minerals deposited in the open. Inside geodes, amethyst and other silicates can get quite large within the open space of another rock. Usually, geodes are made from gas bubbles trapped in areas where the mineral can grow to large and beautiful sizes.

CLASSIFYING MINERALS While you can classify rocks as pretty or interesting, you can't use those terms when sharing legitimate information about the rock or mineral before you. Here are some good classification categories that will help you both identify and talk about rocks. Most minerals can be identified by their visible properties, although real mineralogists often use microscopy to nail down the details of the mineral. When classifying minerals, look for the color you see, the streak, and the luster first. Color actually doesn't help much because the same mineral can be different colors. In addition, you can have real gold looking a lot like fool's gold, which is iron pyrite. Quartz is purple if it has a bit of iron in it; if not, it will be clear in color. Purple in quartz means it is really called amethyst. Next, check the streak, which is the mineral's powder color. It doesn't vary nearly as much as color so it is a better measure of what the mineral really is. Quartz has no streak; many others don't either. Simply scrape it across any unglazed white porcelain plate. Pyrite, which is gold in color, has a black streak, while real gold has a goldencolored streak. Hematite is black but has a reddish brown streak. Luster is how well the light shines off a mineral. You can also describe it as how metallic it is or non-metallic. Iron-pyrite has a metallic luster as the light shines off it. Quartz is non-metallic. Here are some common lusters and what they really look like in layman's terms: •

Amantadine – sparkly appearance like a diamond

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Earthy – dull or clay-like appearance

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Resinous – looking like tree sap resins such as sulfur

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Pearly – looking like a pearl

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Silky – having long soft fiber-like appearance

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Vitreous – looking like glass or like quartz

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Metallic – looking like a shined or polished metal

Hardness is an interesting feature of a mineral. Aren't all rocks hard? It turns out that you can measure the hardness in the field if you need to. You just need a few reference samples for comparison. The Mohs hardness scale is a great way to do this. We will talk about how you can do it too in a minute. Next, we get cleavage and fracturing of a mineral. Crystals are easy to break in certain shapes and directions but not in others. How a mineral fractures will be unique to that type of mineral. Minerals with cleavage will break along certain planes but not others. The planes will be a smooth surface. You know, for example, that salt crystals are cubic if you've seen them up close. This is what halite looks like as well when you cleave the rock. Mica cleaves into sheets but just in one direction. If you try to cleave it the wrong way, you simply get mush. Other minerals are more interesting and form octahedrons or other interesting shapes. Many gemstones are cut along their cleavage lines to achieve the most attractive appearance. Diamonds like to cleave as octahedrons, for example. A fracture is not the same as a cleavage plane. Fractures break the mineral in ways not along the cleavage plane. Minerals are fractured in different ways unrelated to the substance in the mineral. Metals will fracture with splinters or with jagged edges, depending on the situation. Quartz will fracture with smooth or curved surfaces. There are so many different characteristics you can have with regard to any given mineral that might identify it. Here are a few: •

Can it fluoresce under UV light? It might be fluorite.

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Is it magnetic? It might be magnetite.

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Is it radioactive? Don't panic. It is probably uraninite.

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Does it bubble in acid? It's probably calcite.

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Does it have a rotten egg smell? It is likely sulfur-containing.

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Try tasting it – halite is salty.

THE MOHS HARDNESS SCALE The Mohs Hardness test was invented by Friedrich Mohs in 1812. The scale is based on 10 distinct minerals that have different degrees of hardness. They range from talc at a level of 1 to diamond at a level of 10. All but diamonds are easy and cheap to find. They are in order from soft to hard: 1. Talc 2. Gypsum 3. Calcite 4. Fluorite 5. Apatite 6. Orthoclase 7. Quartz 8. Topaz 9. Corundum 10. Diamond Figure 25 shows these rocks in a kit:

Figure 25.

So, how do you do this test? Basically, you scratch one mineral against another. If you have one scratch the other, the first one is harder. If you use specific minerals as part of your study of hardness, you can identify a mineral's content or at least get a good range of whether its hardness is 3 versus 4, for example. If two rocks can be steady enough to do this test, you can get a good comparison against a known sample. Quartz is a good sample to have because it has a medium hardness of 7 and is easy to come by. You can also use original copper pennies or steel files to measure an unknown. They make fancy geology picks that have different hardness levels numbered on them. The hardness scale is in reality not linear. Diamonds at ten are not twice as hard as apatite at 5. The other thing you should know is that there are harder things than diamonds. A substance like lonsdaleite and a wurtzite alloy are harder than diamonds and are very rare. The Vickers Hardness Scale reflects the relative hardness of minerals in a more realistic way. It measures the hardness by looking at the resistance to pressure of a mineral and not by scratching it. It goes as low as 27 for talc to as high as 10,000 for diamonds. The

Mohs scale is much more convenient and inexpensive compared to the Vickers test but they both can be used by mineralogists. Remember too that hardness depends on the direction of the mineral you are pressing or scratching on. If you test the hardness parallel to the long axis of a crystal, you might get a 5 but if you test it parallel to the short axis, you'd get a 7. This is because of the different ways a compound will bond with another neighboring compound. This is how gemologists base the cutting of gems like diamonds for the best shine and polish.

MORE ON SILICATE MINERALS Silicates are so common that you'll find them in every part of the world and in most grains of sand. When we think of the term "crystal", we are usually talking about quartz crystal. Quartz and other silicates have some combination of oxygen and silicon in varying forms – usually with one or more elements mixed into a larger molecule. Quartz is SiO2 chemically, while Olivine is SiO4 plus magnesium or iron. While seemingly so similar, they have widely differing properties. Silicates are ionic salts based on a tetrahedral shape. The silicon atom is in the middle with four oxygen atoms sticking out. This is a very stable tetrahedral molecule, often found in groupings. The bond between silicon and oxygen is extremely strong. There are about 25 common types of silicate molecules in nature. This is because the base silicate molecule can easily polymerize to make others. You can get chains or sheets of these structures at any given point in time. Olivine is a simple silicate. It has the silicate molecule of SiO4 plus magnesium and iron. The silicate molecule is an ion that is negatively charged. Like any salt, it will form a salt with either magnesium or iron, giving this rock a dark or dense coloration. Olivine does not cleave because there is no polymerization of the tetrahedral shapes. Take these same tetrahedrons and put them in chains to get amphiboles and pyroxenes. The chains bond to any of the major cations like calcium, magnesium, or iron. Bridges form between the chains in some cases. If there are no bridges, you'll get the pyroxenes, which are single-chain polymers of the silicate molecules. These are also dark in color. Pyroxene forms the dark-colored mineral in gabbro. Amphiboles like hornblende is a 85

double-chained silicate molecule that can support many different metal cations, like iron, magnesium, aluminum, calcium, and sodium. Micas are silicates that have sheets of polymers. These sheets explain why they are so flaky. Only chemical bonds called van der Waals forces, which are weak forces between molecules, bind these sheets together. Clays are also sheet silicates that have water within the molecular structure. Water keeps the sheets slippery with respect to one another. This is great for pottery making. Firing the clay drives the water out, leaving a sturdier product. Biotite and muscovite are both types of silicate micas. They differ in the number of cations in them. The muscovite has potassium and aluminum in it, while biotite has only magnesium and potassium in it. Quartz is just SiO2, which is balanced and not a charged ion. Feldspars have 25 percent of the silicon atoms replaced by aluminum. The charge is different so you need potassium, sodium, or calcium to make potassium feldspar or plagioclase feldspars. You should at least know what these main minerals look like: pyroxene, hornblende, muscovite, olivine, garnet, biotite, K-feldspar, quartz, and plagioclase. With these in mind, you can identify most surface rocks on earth.

NONSILICATE MINERALS Nonsilicate minerals are those that don't have the silicone and oxygen tetrahedral ion. These are less common but often extremely important to the world's economy. Iron, lead, copper, and other major metals come from the earth in various forms. There are different groupings of these —many of which you will recognize. The native elements are usually the precious metals, such as platinum, copper, gold, and silver. These can exist by themselves or bind in an ionic way to make another compound. Carbonates include dolomite and calcite. These are based on some salt that has the carbonate ion in it. Lime and cement are carbonates. Oxides are also common because oxygen seems to be highly reactive. It is also very abundant. Hematite is an oxide made from iron and oxygen, having the chemical formula Fe2O3. Magnetite comes from iron, and bauxite is an aluminum oxide. 86

Sylvite is a potassium chloride salt, just like halite comes from sodium chloride. Lead, copper, and even mercury can have ores made with sulfur. A few of these are cinnabar and galena. Sulfates are used for many purposes. Epsom salts is a magnesium sulfatecontaining substance, and gypsum is a sulfate used to make sheetrock. Phosphates like apatite are the same thing as what you'll see in bones and teeth. Calcite and dolomite are interesting because you see so much of it in sedimentary rocks, such as limestone and dolostone. The interesting thing about these is that they have a great many small fossils in them. Most are marine fossils. Look for seashells or crinoids in dolostones that date back to Precambrian times. A lot of calcite comes from the breakdown of seashells coming from ancient seas. Calcite in crystalline form have birefringence, which means that light goes in and then splits to travel two different pathways. You will see double images of things that you see through it, which makes it a good tool for geologists. It actually polarizes light to make microscopes so you can study other rocks or minerals. Notice how so many of these minerals are salts. Some will dissolve in water. The carbonates don't generally dissolve in water, which is a good thing since seashells are made from them. Calcite does not agree with acid, however, which is why a small bottle of hydrochloric acid should be in your geologist kit. All salts like this that are made when water evaporates are known as evaporite minerals. Oxides are easy to spot, especially when oxygen mixes with iron. This is essentially rust and leads to the rust color of rocks in many parts of the United States. There are red cliffs made of sandstone in Utah that come from quartz that has been coated with iron oxide on the outside. Hematite, limonite, and magnetite are all forms of iron oxides. The formula is the same but the way they are connected will differ to make the varying appearances of these substances. Other interesting oxides include corundum, which is a type of aluminum oxide. Corundum is the base stone for both rubies and sapphires. Sulfides have sulfur in them along with a metal ion. Iron pyrite is essentially iron sulfide or fool's gold. The mineral called chalcopyrite is a copper and iron sulfide. Galena is a lead sulfide used to make lead, and sphalerite makes zinc because it is zinc sulfides.

These sulfides all help to make the main minerals industrially, like lead, zinc, and copper. So many more of the important metals we get come from sulfide ores. Phosphate is an ion that has a tetrahedral shape. It is easily mixed with other ions to make a phosphate salt. Apatite is a phosphate salt that mixes with fluoride, chloride, and calcium. Turquoise is a gemstone made from a phosphate that contains molecules of water and plenty of copper and aluminum. Native elements can all produce minerals. Most of these are the metallic minerals like copper, platinum, silver, and gold. Diamonds are essentially the same carbon as you'll see in graphite. The only difference is that a lot of time and pressure went into making diamonds. This is why the interior core of the earth probably contains a lot of diamond material. Sulfur is a non-metallic substance you might see in its native form after it is emitted from volcanic fumaroles.

KEY POINTS IN THIS CHAPTER •

Minerals must satisfy certain criteria to be called minerals. They must be inorganic.

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Minerals form a specific crystalline shape, based on their chemistry.

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Minerals have specific identifiers, such as color, density, hardness, luster, and cleavage.

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The Mohs hardness scale is used to tell the hardness of minerals in the field. It is a linear scale from 1 to 10, with 10 being attributed to diamonds.

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Minerals are either silicates or nonsilicates. Silicates are more common and are made from some combination of silicon and oxygen in tetrahedral shape.

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Nonsilicate materials occur in many kinds, mostly as salts of varying kinds. Ores are made from metals and are used to extract many precious metals.

CHAPTER 5: QUESTIONS AND ANSWERS 1.

What is not true when identifying minerals? A. A mineral must have a crystalline structure B. A mineral must be made of a single element C. A mineral must be hardened at room temperature D. A mineral must be inorganic

Which gemstone is not considered a mineral? A. Amber B. Peridot C. Garnet D. Sapphire

You have a mineral that is green in color and notice it shines up brightly under UV light. What is this called? A. Calcite B. Fluorite C. Olivine D. Quartz

You are making a mineral out of a compound in water. To have the biggest crystals, what is generally the most important factor to allow this to occur? A. High temperatures B. Low pH C. High salinity D. Longer time

What element makes amethyst so purple in color? A. Manganese B. Copper C. Iron D. Magnesium 90

You see a bright gold piece of mineral and want to see if it is real gold. If it is gold, what colored streak will it have? A. Gray B. Gold C. Black D. Green

What basic shape is any silicate molecule in rocks? A. Thin needles B. Cube C. Tetrahedral D. Hexagonal

What is not a metal cation that can form a typical silicate? A. Magnesium B. Iron C. Aluminum D. Lead

You are mining for zinc and copper. What type of ore do you get these from? A. Their sulfides B. Their oxides C. Their chlorides D. Their carbonates

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What mineral is not a native element mineral? A. Diamond B. Copper C. Gold D. Steel

CHAPTER 6: IGNEOUS ROCKS IN DETAIL In this chapter we will get into the details of igneous rocks and their formation. Igneous rocks are literally born out of fire – the first rocks to be spit out of our molten interior. After reading this chapter, you will understand what's in magma and how it turns into the rocks you see all the time. Magma is more than just underground lava. You will see the amazing things that happen when it cools and the ways the minerals precipitate out of it when that occurs.

WHAT IS MAGMA? You know by now that magma is the underground molten material that spits out of volcanoes. There are just eight major elements in magma. In order of amounts, you have oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Oxygen and silicon alone make up about 75 percent of magma, so you can see why silicates are so important. Of lesser significance are hydrogen, carbon, and sulfur. These often end up making some kind of gas: carbon dioxide, water vapor, and hydrogen sulfide. These are things you see emitted mainly from volcanoes and bubbling springs. Igneous rocks come out of magma as it cools or perhaps from rocks close enough to the heat of magma to melt themselves and then cool later. Rock materials all melt and crystallize at different temperatures. You might get the partial melting of a part of a rock but not another part. The parts that don't melt often cluster together or crystallize into a mineral. If the heating is extensive, however, everything goes into the magma melting pot. What this means is that both the substance and the melting temperature matter. While heat is important, there is more to rock melting than that. The term "decompression melting" means that something is near the melting point but is still solid when the pressure around it decreases. This pushes the process toward melting, even if the temperature hasn’t really changed. Rocks can do this, depending on where it

is in the mantle. Hot rock moving toward the surface will have less pressure and will begin to melt. Flux melting can happen too. This is true for rocks when there is water added. Water will shift the melting curve so that wet mantle melts at lower temperatures compared to dry mantle. This means that all of these components – rock content, temperature, water presence, and pressure – all affect the melting ability of rocks in the mantle of the earth's crust. Rock partially melts on earth in a variety of situations. Plate tectonics contributes to this in different ways. Mantle plumes are areas where magma gets pushed nearer to the earth's surface. Wet mantle that subducts beneath the upper layers will melt as it gets sucked under the upper crust area. In these regions, partial melting of the silica components will occur as the rock sinks. Some components melt more so than others, so melting is uneven. . Hot spots are seen with volcanic islands, mid-oceanic ridge areas, subduction zones, and along continental rift zones. These are where the magma rises. Magma plumes often give rise to shield volcanoes full of lava. Silica will always melt earlier than basalt rock. At temperatures above 1300 degrees Celsius, all magma will be liquid. Then as it cools, the silica rock crystallizes earlier than the basalt, forcing the rest of the magma to be thicker in its consistency.

HOW MAGMA TURNS TO ROCK There is a sequence of reactions that happen when magma cools; these are called the Bowen reaction series. It is what explains the that magma can be liquid but will also have solid crystals in it. Olivine crystallizes first; any silica left over after this has crystallized mixes with the olivine to make pyroxene. Once pyroxene is formed, there will be a further reaction to create amphibole, and then biotite – all provided there is enough silica to finish the transformation. Pyroxene and plagioclase feldspar crystallize at the same time. Plagioclase has lots of calcium in it but as it cools, it will have more sodium in it. This is a continuous series, starting with calcium-rich plagioclase and becoming sodium-rich. This isn't what 93

happens with the olivine parts. They are discontinuous, leading to distinctly different substances. So, what do you get as rock cools? It depends on the rate of cooling. You can get nearly pure muscovite mica, quartz, and potassium feldspar, especially if there is a lot of silica tetrahedrons left after the magma has cooled. Especially rich areas of silica will finally cool this way, sometimes making giant crystals. What this means is that the amount of silica in the magma makes a big difference in how the rock turns out. It will continue to react this way until all the silica is completely used. There are three major outcomes: 1. Mafic – this is rock that has less silica in it – less than 50 percent. 2. Intermediate – this has slightly more silica in it – about 60 percent. 3. Felsic – this has a great deal of silica in it, about 75 percent. The oxide concentration also matters a great deal. Aluminum and iron oxides are the most prevalent. Mafic cools in a specific way that is different from the others. Olivine is made when the silica combines with both magnesium and iron. What's left over goes to make calciumcontaining plagioclase and any after that goes to make pyroxene. This is mostly the extent of it. If it cools underground, it's called gabbro. If it cools more rapidly above ground, it's called basalt. These have the same composition. Figure 26 is basalt that has holes in it because of rapid cooling:

Figure 26.

Felsic magmas are different. They crystallize at cooler temperatures and get to the pyroxene phase before making much olivine. Plagioclase predominates resulting in more sodium-rich plagioclase, leading to potassium feldspar and much more quartz. This will have more white than black and very little mica in it. This is because there isn't a lot of aluminum or hydrogen needed for this mica material. Granite and rhyolite are the end result. Intermediate magma cools to make diorite or andesite and looks about 50:50 black and white. Intrusive rocks of any igneous rock are those that cool underground. Extrusive rocks are those that cool above ground. Andesite cools above ground while diorite cools below. There are other processes within the magma chamber to consider. Mafic rock is runny because the crystals form early and settle at the bottom of any magma chamber. This removes this rock out of the melting equation, leading to more felsic rock at the top of the chamber. This interesting process is called fractional crystallization. If the sunken 95

olivine remelts later nearer to the center of the earth, it is more mafic than it was in the first place. If the magma is too thick, cooling will be more predictable. In an eruption, however, magma will move up and out of the magma chamber or may just move toward the surface and cool more quickly. The rest of the rock will often have a fine structure to it with respect to its quartz crystals. Porphyritic rock is rock that has a matrix of fine crystals with larger crystals in it. Look for different crystal size to call a rock porphyritic. Figure 27 shows you the different magma temperatures and how the different types of rock crystallize:

Figure 27.

SILICATES IN IGNEOUS ROCK Magma has just a few elements in it –the eight recently mentioned plus tiny amounts of titanium and phosphorus. Because of the high oxygen and silicon content of magma, it is essentially defined by these two elements. The viscosity of the magma, the temperature of the environment, and the gas content of the magma also count toward the rock's appearance in the end.

Gases are going to be in the magma. If you see bubbles, they will settle into porous vesicles in a process known as vesiculation. If the pressure is great enough, it will escape. If not, it will produce a frothy, light-weight stone. Vesiculation can occur if crystallization happens in the stone. It can also happen if there is sudden decompression of the magma. The latter is referred to as the first boiling. Crystallization explosivity is called second boiling. Thin magma explodes more readily than thicker magma. Mafic is low in crystals, thin, and more likely to just spill out of the earth. Felsic magma is so thick that, if any activity happens, it will be explosive.

IGNEOUS TEXTURES Igneous rocks will have different textures. These are use to describe the rocks and classify them. The six textures you should know about are these: •

Aphanitic – this is rock that you see when the magma cools so quickly that they don't ever form large crystals. They are often extrusive rocks. You will see this texture in andesite, rhyolite, and basalt.

•

Phaneritic – this means that the crystals are visible to some degree. You will be able to see them with the naked eye. Gabbro, diorite, and granite are all phaneritic stone.

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Glassy – this is also called vitreous. These happen when crystals can't occur and glass is made without crystals in them. Obsidian is an amorphous glassy black rock.

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Pegmatitic – this is rock that happens when minerals get very large – up to several meters in size. Figure 28 is pegmatitic because it’s basically a crystal of some kind without much basalt or gabbro stone:

Figure 28

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Pyroclastic – this is when explosive eruptions happen to blast lava into the air, giving rise to something called volcanic bombs.

•

Porphyritic textures – this is when the cooling rate of magma varies over time. Large crystals are formed with slow cooling before sudden rapid cooling will contribute to much smaller crystals. The large crystals are called phenocrysts.

HOW TO NAME IGNEOUS ROCKS You already know how to do this for most rocks. You need to understand more clearly why there are pink streaks in some igneous rock and not in others. There are different naming properties depending on how much ferromagnetic silica products are in the rock. High quantities are in amphibole, biotite, pyroxene, and olivine. These will be very dark in general.

You should remember that the felsic rocks will often be high in quartz, potassium feldspar, and plagioclase feldspar. These will be pink or white. Those that are extrusive are called rhyolite or andesite. The intrusive ones are granite and diorite. The mafic and ultramafic rocks are going to be varying dark shades. You'd get gabbro and peridotite, which are intrusive. Extrusive rocks of this type include basalt and komatiite. Figure 29 is a good cheat sheet on naming igneous rocks:

Figure 29.

INTRUSIVE IGNEOUS ROCK Intrusive rocks involve magma below the surface. Magma isn't as dense as rock so it will work its way toward the earth's surface, if possible. It will fill in any existing cracks and melt the rocks with cracks in it. This is called country rock. Country rock might fall into magma, which is called stopping of the rock. These melted fragments are called xenoliths. Look for odd-shaped black mafic rock within harder rock like granite to find xenoliths. Figure 30 shows one of these:

Figure 30.

A pluton is a piece of magma that worked its way to the surface but did not make a volcano. Some will be imbedded in country rock. A big pluton with an irregular shape is a batholith or a stock. A batholith has a large, exposed area of more than 100 kilometers squared, while a stock has a smaller surface area exposed – less than 100 kilometers squared. A large area of batholiths is the Coast Range Plutonic Complex – starting in Vancouver and ending in the southeastern region of Alaska. 100

Sheets of pluton can be parallel to or angled with respect to the sedimentary rock around it. A sill will be parallel to the layers, while a dyke is discordant or angled with respect to the layers. Sills tend to creep in between layers, while dykes push up underneath to form some type of non-horizontal section of magma. A laccolith is a very thick sill that created such a thick layer that it deformed the rock above it. A pipe is any cylindrical place where magma shifts from one place to another. Pipes can connect different plutons to one another.

DIAMONDS AND THEIR ORIGIN Diamonds are not made from coal as many people think. Coal comes from the carbon you see in land plants and most diamonds on earth predate that time period, so the idea that they come from coal is not feasible. Diamonds are made from carbon but unlike coal, they come from vertical magma pipes and not horizontal layers. Coal forms much more superficially than diamonds as well. So, how do diamonds form? Diamonds we use commercially now come from very deep volcanoes emitting magma from deep within the earth. The magma comes up quickly, passing through the zone where diamonds are stable, ejecting xenoliths that contain diamonds. This zone where diamonds are held within the earth is called the diamond stability zone. Open-pit mines also allow for diamond collection because they are found in sedimentary rocks that are in rocks or streams. They were once formed about 90 miles below the earth where the temperatures are high – 2000 degrees Fahrenheit. Now you have both pressure and temperature needed to make diamonds. Plates where the continents are most stable have these diamonds in them. These are the mid-continental plate areas. Don't expect to find large diamonds anywhere, but you might get lucky. Where did all this carbon come from? It was carbon that was trapped within the earth at the time it was formed and never when plants were on earth. They may have gone deeper in some areas due to subduction of mantle into the magic sweet spot where diamonds are made. Surprisingly, diamonds can come from asteroids that have impacted the earth with enough force to create diamonds. Again, pressure and heat make diamonds. These are very rare sources of diamonds, however.

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Diamonds used in things like manufacturing and cutting tools are sometimes artificially made – simply by having heat and pressure create these tiny diamonds for industrial use. These lab-created diamonds mean we don't have to find and use those gotten from the earth to make a large number of them.

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KEY POINTS IN THIS CHAPTER •

Igneous rocks are mostly silicates that are born out of magma.

•

The silica content and the cooling rate both affect what the end state of the rock looks like.

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Magma is on a continuum ranging from mafic type, which is silica-poor, to felsic, which is silica-rich.

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The type of rock you see depends on chemical reactions taking place between the atoms of iron, magnesium, aluminum, sodium, and potassium and the silica tetrahedron.

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Igneous rock can be intrusive, made within the earth, or extrusive, cooled external to the earth's surface.

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Magma rises to the surface to make sills, dykes, laccoliths, and other formations coming up from plutons rising out of magma pools and settling into layers of sedimentary rock.

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Diamonds are carbonaceous and made from very deep parts of the earth.

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CHAPTER 6: QUESTIONS AND ANSWERS 1.

What is not one of the major elements in the earth's magma? A. Silicon B. Iron C. Lead D. Oxygen

Which is not a component that controls the melting process of a rock? A. Presence of water B. Pressure C. Temperature D. Sunlight

In gabbro rock, what will you not see as part of the rock? A. Pyroxene B. Olivine C. Calcium plagioclase D. Quartz

What is the equivalent of gabbro that cooled above ground more rapidly? A. Andesite B. Diorite C. Basalt D. Granite

When igneous rock undergoes vesiculation, what will you see in the rock? A. Hard and dense stone B. Bubbles in the stone C. Blacker stone D. Stone with more crystals in it

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What type of magma is most likely to be explosive if it erupts? A. Mafic B. Non-gaseous C. Thin D. Felsic

A rock that melted and fell into another rock type before getting stuck there into an irregular shape is called a what? A. Batholith B. Stope C. Xenolith D. Country rock

A sheet of magma that comes up to sift between horizontal layers of sedimentary rock and solidifies is called what? A. Xenolith B. Pluton C. Country rock D. Sill

Diamonds are made from one main element? A. Aluminum B. Iron C. Sodium D. Carbon

10.

The diamonds used to make diamond cutting tools most come from what source? A. Laboratories B. Streams C. Volcanos D. Outer space

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CHAPTER 7: VOLCANOES This chapter delves into volcanism and the volcanoes we have on earth. Volcanoes help dispel the heat from inside our planet and contribute to new land formation in some parts of the world. Magma is extruded from deep within the earth through volcanic activity. You already know that lava is just surface magma. You will learn that there are several types of volcanoes and volcanic eruptions all over the world. We will also discuss how volcanic eruptions might be predicted.

EARLY VOLCANIC ACTIVITY Volcanoes happen as the earth expels its internal sources of heat. Magma must get close to the earth's surface to do this, which means plate boundaries are great spots for volcanic activity. Subduction zones are also places for pooling magma that is rich in silicates. Remember the hot spots we talked about? Those are areas where magma is able to reach the surface through thinner areas. The volcanoes from Hawaii are in a hotspot for sure. The earth is only slightly older than volcanoes, which arrived on earth at least 4 billion years ago. There really wasn't much time when earth was completely molten. There was probably a huge amount of volcanic activity in the beginning – both because the magma was close to the surface and because the earth was very hot. Volcanic gases and volcanoes contributed to a great deal of the geology of early earth but not necessarily just by spitting out magma. The main gases emitted by all volcanoes then and now are carbon dioxide and water vapor. Back at the time of early earth, however, there was probably more hydrogen sulfide gas and methane gas and fewer oxygenated gases. Oxygen exploded in the atmosphere around 2.4 billion years in the past, but not immediately after the bacteria that were photosynthetic began doing their job making oxygen as a waste product. This is because the oxygen was sucked up for another

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purpose. Early earth had a mantle that wasn't very oxidized but was just waiting for oxygen to react with it. The gases emitted from early volcanoes reacted with oxygen as they were emitted. Hydrogen gas may have been one of these, reacting with oxygen to make water. It was only when the gases were mostly mixed with oxygen from bacteria that real oxygen gas could accumulate. As the mantle itself became oxidized, fewer of these gases were emitted and more gases that were already oxidized were more likely to be emitted from newer volcanoes. It's hard to know much about early volcanoes as the oldest volcano on earth – Mount Etna – is only about 350,000 years old.

VOLCANO ANATOMY What are the pieces and parts of a volcano? They all look different but have similar parts to their anatomy. This brief glossary covers things you'll see in figure 31 on volcano anatomy:

Figure 31.

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The main feature you'll see is the magma chamber beneath it. The magma is molten and hot, sitting up to 10 kilometers below the earth's surface. This is what is emitted out of it as lava. The vent is the top part of the volcanic mountain where most of the magma comes out. This is where you see the main eruption. You can have side vents off the main vent as well. Magna and lava can be thin or thick. They can also be gaseous or non-gaseous. Lava that can flow downhill will do this as a typical lava flow. Some lava is ejected wildly out of the vent as a volcanic bomb. These are at least 26 inches in diameter, cooling quickly as they fly through the air as extrusive igneous rocks. As lava builds up, it forms a lava dome or circular mountain that is caused by slowly moving thick lava. An eruption column is the hot ash and gases that are released when there is a volcanic eruption. Inside this hot cloud, the air is electric so that you might see lightning and thunder. This leads to an eruption cloud or a falling cloud of ash that falls like snow after an eruption. Ash is dangerous and can suffocate living things. You might see this up to 12 miles above the volcano itself with ash falling thousands of kilometers away from the eruption. Tephra are pieces of magma that break apart after being ejected from the lava vent. They can be giant boulders or tiny ash pieces; tephra are very dangerous. Acid rain is a common occurrence which happens when sulfur dioxide or nitrogen oxide coming out of the volcanoes mixes with water in the air. Pyroclastic flows are very deadly. The stuff coming down the mountainside is very hot, gaseous, and fast-moving. Tephra are mixed in with these gases to make this deadly cloud. Lahar is also dangerous. This is a mixture of volcanic gases, ash, and local water to create a giant mudflow that can destroy whole towns. Fumaroles are any holes, fissures, or cracks near volcanoes where heat, gases, or magma come out. Sulfur gases come from these areas, for example. Cracks are also openings that reach down into the magma pool.

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TYPES OF VOLCANOES There are four types of volcanoes to know about. These are called cinder cones, shield volcanoes, composite volcanoes, and lava domes. Cinder cones are the basic volcano. Generally, just one single event ejected a lot of gas and lava into the air. The lava breaks up easily and fall to make what is called cinders in order to build a cone-shaped elevation around the vent. Many have a small crater at the top and few rise more than 1000 feet into the air. You will see lots of these in the western region of North America as part of the normal terrain. Lava flow is the last part of the event – after the eruption and formation of the cone itself. While not tall, these cones can be very wide at the base. Composite volcanoes area also called stratovolcanoes. This is because they are layered over multiple eruptions. Their sides are steep and relatively symmetrical. Expect to see alternating layers of cinder blocks, lava bombs, and ash – rising as high as 8000 feet above their bases. Many of these are around the world, such as Mount Fuji, Mount St Helens, Mount Hood, and Mount Rainier – among others. You will often see one or more vents with at least one crater. There will be breaks anywhere in the crater or through fissures along the side of the mountain. Lava will form dykes after it solidifies inside side vents. There is often an extensive conduit system for magma to travel upward through the mountain in one way or another. Over time, the weathering of these dormant volcanoes will eliminate the cone, exposing magma at its base. You might see a dyke complex or a magma plug at the top to indicate that the volcano hasn't erupted in a long time. Crater Lake in Oregon is an old crater that collapsed so much that it formed a waterfilled lake. There isn't much of an elevated cinder cone or composite volcano left except for Wizard Island near the edge of the lake. Crater Lake is essentially a caldera, which will be discussed soon. Figure 32 is an image of crater lake and its single island:

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Figure 32.

Shield volcanoes are made of lava flows almost exclusively. Lava pours out everywhere as fluid from a single vent or cluster of vents near the top. They are called shield volcanoes because of their shape, where the mountain is broad and slopes gently. There is a great deal of basaltic lava in these built-up volcanoes. There are frequent rift zones where lava erupts from the sides. Mauna Loa is currently the world's largest active volcano because its base is actually at the bottom of the ocean – about 15,000 feet beneath sea level. Above sea level, it is nearly that high as well. In some cases, there is little elevation – just lava pouring out of vents onto broad plateaus instead of mountains. This is seen in Idaho, parts of Oregon, parts of Washington, and Iceland. Lava here is thick – as much as one mile thick in places. Lava domes tent to be very small and bulbous in nature. The lava is too thick to do much so it piles up near the vent. This is what forms the dome shape of the volcano. Steep

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lava flows can come off these in places. These steep flows are called coulees. Many domes are seen within craters of other larger volcanoes. Any expansion you see is from within the dome itself. It is possible for these to erupt violently, despite their small size.

DIFFERENT VOLCANO CHARACTERISTICS Other than their appearance, there are other differences between volcanoes of varying types. Most composite volcanoes are found along plate boundaries in subduction zones. They tend to create andesite magma with more silica and gases than shield volcanoes. They are also more explosive and more likely to leave behind acid rain. These don't erupt as much as shield volcanoes, but are violent when they do. On shield volcanoes, look for them on divergent plate boundaries where earth is being made and plates are separating. The magma is basaltic and hot. It is low in silica and low in gas content. These are not explosive volcanoes, having non-acidic lava. There is no layering and more frequent eruptions. Lava tubes form when molten lava travels beneath solidified lava and then flows through in its molten state, leaving a tube behind. A Caldera can be seen with any type of volcano and is made when a magma chamber collapses.

VOLCANIC ERUPTIONS There are differences with volcanic eruptions; some are violent and full of ash and tephra, while others flow relatively gently as they erupt. Eruption types are often named after specific volcanoes that have that type of eruption. Some will have a mixed eruption pattern. There are three main types of eruptions you should know about. There are also others that are minor patterns of eruptions. Let's look at the three different patterns: 1. Gas gets released at times of decompression. 2. Particles get ejected when steam erupts. 3. Chilling of magma suddenly happens on content with magma and contracts.

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Explosive eruptions involved gas and high amounts of magma and tephra ejected into the sky. Effusive eruptions involve outpouring of basaltic lava without much of any explosive activity. The most extreme effusive volcanic eruption is the Hawaiian eruption, while the most explosive eruptions are the Plinian eruptions. Not all eruptions are emitted out of the top of the structure. Remember that Hawaiian eruptions happen along the rift zones and not necessarily from the top. There is a scale called the VEI or volcanic explosivity index, which is a scale that runs from 0 to 8. It is used for both modern and prehistoric eruptions in ways like we now use the Richter scale. It is not linear but logarithmic. This wide variation means that most eruptions today are between 0 and 2 on the VEI scale.

LAVA FLOWS AND PYROCLASTIC FLOWS Let's talk about the different type of lava flows and eruptions you'll see in more detail. You can see how they range from fairly mild to very dangerous eruptions. Magmatic eruptions are those that have some intensity and gas behind them. Tiny ones are seen as lava fountains and big ones are seen as high as 30 kilometers in the sky. This is bigger than the eruption that destroyed Pompeii in 79 AD when Mount Vesuvius erupted. Hawaiian eruptions are the effusive kind you see in Hawaii. These are relatively tame volcanoes that erupt with small volumes of basaltic lava. Most eruptions are not in the center of the volcano but erupt all over the volcano in rift zones. Because of the way these eruptions look, they are often called a curtain of fire when they erupt. Hawaiian eruptions last a long time. A volcanic area on Kilauea has been erupting for more than 35 years. Strombolian eruptions are named after Stromboli, which has been erupting for centuries now. These are mostly driven by gas bubbles that burst through the magma. These bubbles will burst and pop loudly with magma ejected in the air. You will hear these occasional blasts when the bubbles pop. Despite the sound, they do not cause a great deal of damage. Expect a few volcanic bombs to be ejected in the air as well.

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The term "vulcanian eruption" comes from the volcano called Vulcano, located in the Tyrrhenian Sea. There is magma of intermediate viscosity so that gases have a hard time escaping. Gas will build up and will eventually pop to the surface in a more violent eruption than you'd see in a strombolian eruption. These do not get ejected into the air as much, however, and will simply create eruption columns that are up to 6 miles in the air. These are andesite eruptions and not basaltic like Hawaiian eruptions. Expect shortlived events with plenty of blocks and volcanic bombs being ejected into the air. Pelean eruptions are named after a volcano called Mount Pelee in Martinique that erupted in 1902. It was a major volcanic natural disaster with plenty of dust, gas, ash, and pieces of lava fragments that blow out of the volcano's middle, leaving behind a large central crater. These are rhyolite and andesite lava fragments driven out of the earth by expanding gas. Often, there is a great deal of pyroclastic activity. These are very dangerous and capable of killing thousands of people. More than 30,000 people died when Mount Pelee erupted at once. Plinian eruptions are similar to the one that was ejected from Mount Vesuvius in 79 AD. There are dissolved gases that build up within the magma. These bubbles are smaller and in vesicles until they rise and come together in the upper chamber. Once they get big enough, they explode out of the narrow conduit. These reach very high levels – up to 45 kilometers in the air. The plume gets into the stratosphere and the ash can spread widely. Those with rhyolitic lavas are most explosive, with eruptions lasting up to several days. The difference between these and strombolian or vulcanian eruptions is the length of time of the eruption. These tend to be longer in duration than most gaseous type of eruption. Pumice will fall everywhere around this type of eruption, just as it happened in Pompeii. The pyroclastic flows and lahars are common and deadly as well. Other Plinian eruptions have been the Toba eruption 70,000 year ago, the eruption of Pinatubo, and the eruption of Mount St. Helen's. These are very destructive in general and are the kind that can potentially kill millions of people. Phreatomagmatic eruptions involve magma as it interacts with water. Magmatic eruptions are driven by thermal expansion, while Phreatomagmatic eruptions are driven

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by thermal contraction because water will quickly contract any hot object that cools rapidly. Expect the magma pieces ejected from these latter eruptions to be fine-grained and more regular in their shape. Rapid cooling might widen nearby cracks made by stress waves as the initial magma cools. The Surtseyan eruption comes from shallow water interacting with lava. These form large water-vapor clouds similar to strombolian eruptions. Water also gets superheated and forms large steam expansions lifting into the sky. They can happen on land if the magma comes in contact with underground aquifers. Most are basaltic and many are relatively continuous when they erupt. Another feature of Surtseyan eruptions are radial clouds that hug the ground due to their density. You might see dunes of deposits in rings around these radial clouds. Accretionary lapilli are accumulations of spherical ash that build up around the volcano. You know you've seen one of these lapilli when you see tons of small spherical ash or lava balls near the volcano or imbedded in the rest of the lava. There are a few of these eruptions in the world, including one in Surtsey, Iceland, one in Mount Tarawera, New Zealand, and one along the Mediterranean Sea in a seamount called Ferdinandea. Submarine eruptions occur under the water. About three-fourths of the total volume of magma ejected through these deep underwater eruptions come out from below the earth's surface. Most of them come out of mid-oceanic ridges. You can get island chains and seamounts from these over time, or if they are very large. Most of these are basaltic but if they are near subduction zones, you will get thicker, more viscous, felsic-like rock ejected and more violent eruptions. These are extremely common but were undetected until the 1990s when equipment was made that could listen for them underwater. Pillow lava is the kind of lava you get from these, but you might also get sheets of lava flowing out of them. There are at least 100,000 of these deep-water volcanoes on earth, but you will probably not see any of them and most are beyond being active at all. Subglacial eruptions are interactions between ice and lava beneath a glacier. They usually occur at higher latitudes on earth and at higher altitudes than most other glaciers. Some make instantly melted water that can lead to flooding and lahars in lower ground areas. A main feature is a flat-topped volcano with steep sides, called a tuya.

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You might see these in Iceland or in areas of Northern Canada. As glaciers become more unstable in a warmer earth, landslides are possible as part of volcanic activity beneath them. Figure 33 shows what a tuya looks like:

Figure 33.

Phreatic eruptions come from steam. You can also call them steam-blast eruptions. If the ground is cold or water is near hot magma, it become superheated, fracturing rock as it explodes. The stuff that erupts is not new magma but preexisting broken rock pieces. You might not see a real eruption but only a lot of rock cracks hidden within rock faces that somehow withstood the high pressure circumstances. Phreatic eruptions can precede giant Plinian eruptions; they can also cause toxic gas leaks, mudslides, and avalanches that can be very dangerous by themselves. You would have been able to see these before Mount St. Helens erupted in 1980.

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VOLCANO SEISMOLOGY Seismic activity will be inevitable as volcanoes are ready to erupt. There are those volcanoes where you'll see seismic activity around all the time, so only an increase in seismic activity will detect an eruption. You will see three types of earthquakes around a volcano: 1. Short-period earthquakes – these are similar to fault-generated earthquake activity. Brittle rock fragments in places and magma gets forced upward. These create A-waves or what are called VT events. 2. Long-period earthquakes – these mean that there is a lot of gas inside the chamber and sound like clanging in your plumbing sometimes. These acoustictype vibrations are called B waves or long-period resonance waves. 3. Harmonic tremors – these occur when magma pushes up against rock underneath the crust. Animals can feel them as buzzing or humming beneath their feet. Gas emissions can indicate an upcoming eruption. These gases escape near the volcano. Much of it is sulfur dioxide, which is a major herald to an upcoming volcanic blast. Mount Pinatubo had this type of activity just before it erupted in 1991. You can also measure areas of swelling where magma is building up. This increase in swelling was seen in Mount St Helens before it erupted. The north face was bulging detectably before the eruption. Normally, the ground deforms in ways only detectable by sophisticated equipment used by volcano experts. In Hawaii, you can literally see the magma moving just under a shallow surface. You can measure the temperature of the ground with thermal monitoring to see if it is heating up. Satellites use infrared imaging, while others use the temperature of hot springs or fumaroles to see if things are heating up near a volcano. Hydraulic equipment can be used to measure the temperature and gas pressures deep within the earth. If you see increased sediment in a river near a volcano, it can be coming from the volcano just about to erupt.

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Remote sensing is possible to measure eruption clouds above a volcano or to see how much carbon dioxide or sulfur dioxide is found in the atmosphere. Hot spots can be seen using remote thermal sensing as well. You also don't have to be near a volcano to detect its geometric changes or to see if there are variations in forest growth before an eruption. Remote monitoring can detect sound using sensors that are triangulated to find out where the eruption is likely.

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KEY POINTS IN THIS CHAPTER •

Volcanoes have existed since there has been crust on earth.

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There are four major volcanic structures – lava domes, cinder cones, composite, and shield volcanoes.

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Not all volcanoes emit basaltic lava, especially near subduction zones.

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Volcanoes range on a logarithmic explosivity scale from 0 to 8.

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Volcanic eruptions can involve one or more vents, gentle flows, explosive gases, and steam, depending on the different types.

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You can somewhat predict the presence of an impending volcanic eruption by measuring different things, such as gas emissions, ground deformation, sounds beneath the ground, and seismic activity.

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CHAPTER 7: QUESTIONS AND ANSWERS 1.

Volcanoes started on earth about how long ago? A. 4.6 billion years ago B. 4 billion years ago C. 2.6 billion years ago D. 1.2 billion years ago

What volcano on earth now is the oldest among all volcanoes? A. Mount Pinatubo B. Mount Vesuvius C. Mount Etna D. Mount Ruiz

What type of volcano began and developed with a single event? A. Cinder cone B. Composite volcano C. Lava dome D. Shield volcano

What volcano type is also called a stratovolcano? A. Cinder cone B. Composite volcano C. Lava dome D. Shield volcano

What feature is seen with shield volcanoes but not with composite volcanoes? A. Ash B. Explosivity C. Acidic lava D. Lava tubes

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What feature is seen in composite volcanoes but not in shield volcanoes? A. Andesite lava B. Frequent eruptions C. Found on divergent zones D. Broad sloping sides

What is the main difference between a Surtseyan eruption and a strombolian one? A. Surtseyan eruptions involve the interaction of water and magma. B. There is just one singe giant explosion in Surtseyan eruptions. C. Surtseyan eruptions have little ash. D. Surtseyan eruptions are only seen in deep ocean waters.

You see some accretional lapilli near a volcano. What do they look like? A. Jagged pieces of pumice stone B. Spherical balls C. Giant black boulders D. White ash in layers

What gas emission most signifies an upcoming volcanic eruption event? A. Sulfur dioxide B. Methane C. Water vapor D. Carbon dioxide

10.

What is not easily able to be detected with remote sensing devices in order to predict a volcanic eruption? A. Soundwaves B. Ground deformation C. Underwater temperature D. Sulfur dioxide concentrations

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CHAPTER 8: WEATHERING AND ITS EFFECTS ON GEOLOGY This chapter covers weathering and its effects on geology. Weathering is inevitable and can change rock faces. You will learn how these work with regard to sedimentary rocks and how weathering creates soil. Soil is different all over the world for many reasons. You will see how soil forms and what makes each soil type unique. Weathering can create ore deposits, as you will soon learn.

MECHANICAL WEATHERING TYPES Mechanical weathering breaks down rocks into pieces through several mechanisms. These include temperature, freezing and thawing, plant or animal activity, pressure, and the evaporation of salt. Let's look at these in more detail: Pressure expansion happens when something heats up. If the air pressure around a rocky area drops more rapidly than the temperature, the rock will expand and crack. The cracks can then fall off in sheets called exfoliation or spalling. There can be spheroidal weathering if there is some chemical weathering along the joints in the exposed bedrock. Frost wedging is easy to imagine. Water can seep into a rock and then freeze. As water freezes, it expands, widening the crack further. Eventually the entire thing breaks the rock into pieces. Repeated freezing and thawing will cause the melted ice to creep into even wider crevices, where it can re-freeze. This can happen simply through the day and nighttime temperature fluctuations. Roots can cause weathering from deep underground. Plants and trees have a way of working their roots into any cracks they can find. Some of these roots die off and become petrified to become rhizoliths. Ants, termites, and most earthworms have the same weathering abilities. Over time and in high numbers, you will get weathering of

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rocks as they work their way into any crevice possible. Figure 34 shows root weathering with some rhizoliths in a cliff face:

Figure 34.

Salt expansion is a weathering technique that is a lot like frost wedging. You need to have an oceanic environment where evaporation is possible. When water evaporates, you get salt crystals. These grow and expand inside rocky cracks. When salt does this, it leads to holes in rocks called tafoni. Tafonis then become weak spots in the rock where more weathering can take place. Salt can also leave behind what's called a hopper crystal, which is a square imprint of a salt crystal in softer sedimentary areas.

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TYPES OF CHEMICAL WEATHERING Chemical weathering is the major driving force for weathering in warmer and more humid parts of the world. Minerals can get degraded with natural substances that react with them. Such processes can literally turn a mineral into a soluble ionic compound that can get washed away by running water. This only works where the rock is exposed in some way, but you can see how this could accelerate over time. The smaller a piece of rock the more surface area it has to work on. This means that the process will just speed up as pieces of rock get smaller. Higher temperatures are best for chemical weathering. The best case scenario is for chemical and mechanical weathering to happen along with it. This means that you will get more chemical weathering if there is mechanical weathering to break rocks up into smaller pieces for greater surface area to volume ratios. One chemical reaction involves carbonic acid, which is water and carbon dioxide mixing in clouds. This is what makes rain somewhat acidic. Carbonic acid causes hydrolysis, which means that water mixes with a substance to change its chemistry. Carbonic acid can react with aluminum and silicon-containing feldspars to make molecules that are involved in clay. In other words, hydrolysis takes silicates in feldspar to make clay, metal ions, and ordinary silica. This clay creates fine sediment that goes into making sedimentary rock, such as limestone. Dissolution is essentially hydrolysis that dissolves bedrock minerals and allows the resultant metal ions to remain in water. Certain minerals, such as carbonates and evaporites, are more likely to do this process. More acidic water will turn rocks into dissolved substances much more rapidly. Biological agents can release organic acidic substance onto rocks that accelerate the process of dissolution of rock. Humid and wet areas will also have accelerated dissolution. Remember the Bowen Reaction Series that turned basaltic rock into rocks with more and more silica in it in magma, and that leads to crystals in the rock as it cools? This reaction series indicates that those things at the top will crystallize first and those that will crystallize last on the bottom at lower temperatures as magma rises. The olivine

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and pyroxene near the top will chemically weather faster than those at the bottom. This means that quartz is the least likely to chemically weather. This fact is described by the Goldich Dissolution series, which is essentially the Bowen Reaction Series in reverse. The idea is to demonstrate that olivine and pyroxene are rarely seen in highly weathered rock because they dissolve so readily into water-soluble ions that simply wash away. You might see this phenomenon when you see sinkholes or caves in bedrock that has a lot of carbonate crystals in it. These sinkholes are created by dissolved substances and are called Karst topography. Figure 35 shows the different types of karst topography features you can get:

Figure 35.

Oxidation is a common chemical phenomenon in geology. You've seen this when iron oxidizes to form rust. Iron binds with oxygen to make iron oxide, which is red or rustcolored in nature. If there is a lot of iron in the rock, you'll see it deeper within the rock. Sediment where water and oxygen can get in more easily might have an oxide in it. Like

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your car, iron oxides weather more easily than iron itself. You could get voids in certain rocks where oxides have washed away. The main oxidized substances you'll see are hematite, which is gray or red, goethite, which is brown, and limonite, which is yellow. These are cementing substances that can bind and cause coloration of sedimentary rock. All of the cool layers you'll see at the Grand Canyon and Zion National Parks come from oxidation of iron cementing these layers. Erosion is mechanical in nature; it involves things like gravity, water, ice, or wind. Most of the time, it is liquid water that causes the mechanical erosion seen on earth. Many interesting geological features are a part of erosion and weathering. You already know that there are different resistances to weathering, depending on the rock type. The Grand Canyon and the Hoodoos seen in Bryce Canyon National Park are all major features related to erosion differences between different rock layers.

WEATHERING RATES Which things control the rate of weathering the most? There are several factors to consider, including these: •

What are the properties of the parent rock? As you know, mafic rock weathers faster than felsic rock minerals. Water and calcite cause dissolution of the calcite more than you'll see feldspar dissolve, simply by the solubility of the compound in water. Larger granite rocks have fewer cracks than sedimentary rock, so these will not weather as much. There are more places on Earth for water to weather sedimentary rock compared to igneous rocks.

•

What is the climate like? High rainfall levels and higher temperatures mean that rocks will weather more easily. This means that weathering is faster in hot, tropical environments.

•

What is the soil like? Soils will generally retain water, meaning that rocks with soil on top of them have more weathering. This is because most weathering is chemical and needs water to do this. Also, you'll see bacteria and other

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microorganisms in soil that will promote the acidity needed for chemical weathering. •

Exposure time is important too. The longer an area is exposed to any weathering process, the more likely it is to be affected by the process.

So, when we think of weathering, we often think of things like wind, but chemistry and water often have more to do with weathering than wind. Still, wind does play a role in erosion and weathering.

WIND AND DESERT FEATURES Weathering can happen in a desert just as much as in wetter climates. It just happens at a much slower rate. You need water to have legitimate weathering. Without water, you'll get mechanical weathering as the main part of this process. You also won't get much runoff without water. Desert varnish is a unique weathering feature seen in deserts, for example. It is a thin brown layer of clay minerals from manganese and iron oxides found in dry environments where oxides form but don't wash away. Fine sand that flows due to saltation is a main force for mechanical weathering in a desert. Saltation is essentially the bouncing of small grains along a surface. This saltation zone sandblasts many unique features in the desert. If winds are severe, you might get a blowout, which is a depression left over after materials have gotten blown out by the wind. Some desert features you might see are these: •

Playa – these are dry evaporated lake beds where streams ran in and left water behind.

•

Ephemeral streams – these are areas that are streams only if there are heavy rains. Flash floods can come from these areas that just don't drain quickly.

•

Sand dunes – these are deposits of sand created by shifting winds and variations in sand supply or the addition of vegetation in some areas but not others.

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SOIL Who knew that soil had much to do with geology? Soil is a lot more than dirt, as you will soon see. It is a mixture of minerals, water, air, and organic stuff forming where the geosphere meets the biosphere. Once weathering takes place, the bedrock becomes sediment and as long as the sediment persists, organisms dig into the mineral and make things out of atmospheric gases, water, and sedimentary minerals. This becomes organic soil. Soil is a place where plants, animals, and microbes live and thrive. Humus is the organic part of soil; it is very rich in bioavailable nitrogen animals and plants can use. The main component of soil used by organisms is nitrogen. Animals and plants cannot use the nitrogen in the air but nitrogen-fixing bacteria will easily take nitrogen gas and make it bioavailable for us to use. Interestingly, while nitrogen fixing bacteria are used to make ammonium, amino acids, and other biomolecules in living things, you also get ammonium from decomposing plants. This ammonia gets processed by nitrifying bacteria to make nitrites and nitrates, which are ions with nitrogen and oxygen in them. Finally, denitrifying bacteria takes nitrates and turn them into nitrogen gas again. This is one giant cycle called the nitrogen cycle. Productive soils are those that have a lot of water and nutrients in them. These include the andosols, which are volcanic soils, and soils high in clay content. Soils with little nitrogen in them are not able to grow crops as easily. How do we characterize soils? There are five major components we will look at. These are the minerology, the weathering, the topography, the climate, and the microorganisms found in the soil. Erosion will erode more rapidly on some soil types and not others. The content of any soil will also determine what will grow best in it or if anything much will grow at all. Most of the well-formed soils of the world will have layers called horizons. If you ever see areas where the earth is deeply dug, you will see these horizons. There are names

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and letters associated with each of these important layers. Figure 36 will help you see them visually:

Figure 36.

The O horizon is the organic layer. This is thin and contains plant parts that might be decaying, leaves, and twigs. These will decay into humus. Next is the A horizon, which is topsoil. This is humus that has been mixed with minerals as sediment. This is rained on and has some leaching of soluble minerals and other 128

substances down into the E layer or eluviation horizon. This lighter layer is very mineral-rich as a result of leaching. The B horizon is the subsoil. This is where you have humus and sediment that is removed from the upper soil layers and where chemical weathering is taking place. The upper part of the zone is called regolith, which is porous and has highly-weathered sediment. The Saprolite area or lower zone, where there is parent rock and little organic material. Below these is the C horizon, which is the substratum. Mechanical weathering happens here as bedrock gets broken but not very altered in a chemical way. No organic material exists here. The R horizon is the bedrock. The parent bedrock and some rock fragments live here in the absence of weathering. There are different taxonomic classifications for the various known soil types. There is a difference between volcanic soils and prairie soils. The dust storms of the 1930s in the American Southwest happened because there were too many people trying to develop the prairies without understanding the problems in doing this. They planted crops with shallow roots, replacing prairie plants with deep roots.

SOIL FORMATION AND CLASSIFICATION Soils are given a name that usually comes from where they were first mapped. Soil surveys will be done to determine what kind of soil exists in any given area. This leads to soil taxonomy that uses a soil's color, structure, texture, and related properties. There are several factors that go into making soil. You need to consider a number of variables going into any given soil, including these: •

The parent material. Most soils form in materials coming from elsewhere. Some comes from wind that has blown into an area. Glacial till makes soil that has been moved by a glacier. The material where the soil came from is called the parent material. Some deeper material remains unchanged after it was originally deposited. The texture of sediment in streams depends on how fast the stream is moving.

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•

Climate. Soils are variable with the climates they are in. Climate involves both temperature and moisture, leading to varying levels of weathering or soil leaching. Wind and dryness affect how soil gets distributed. Seasons that are cold will have less chemical weathering.

•

Topography. Slope of the land affect how much moisture it gets and what the soil temperature of the soil might be. Those slopes that are sunnier have a different erosion rate than those not facing the sun. Steeper soils might be thinner due to the effects of gravity.

•

Biological aspects. The plants, animals, and microbes in an area affect the soil. Human activity also affects it. Plants with deep roots will loosen soil. Different types of roots will affect the soil differently. Microbes interact intimately with roots in certain ways that are often symbiotic.

•

Time factors. Soils mature over time and reflect the area's activities. You need to know that soil formation is ongoing and completely continuous throughout time. Buried soil must essentially start over as a new soil type with features seen in most deeper soils.

SOIL ORDERS As mentioned, soil is divided taxonomically into orders. The highest level has 12 different orders, but there are 64 sub-orders among these. It gets even more complex with 300 groups and 2400 subgroups. Let's look at a few of the major orders and talk about what they might look like: 1. Alfisols – these soils are in moist to semi-arid areas. They were once formed in forests or with overlying vegetation, making them productive for crops. 2. Andisols – these are the most productive soils. Found with moderate to high rainfall and cooler areas, you will see these with volcanic materials. 3. Aridisols – these are mostly too dry for most plants and have things like salt and calcium carbonate that get leached out if it is too wet. This is desert soil.

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4. Entisols – this is soil where erosion or decomposition is fast – too fast to make new soil. You'll see the parent material here in slopy areas, dunes, or along flood plain regions. 5. Gelisols – these are soils in cooler areas or in higher elevations where permafrost is located near the surface. Ice churning and frost churning can happen here. 6. Histosols – this is highly organic soil with no permafrost. It is extremely wet here in places like mucks, bogs, or moors. 7. Inceptisols – these are areas in mixed environments with moderate weathering seen in many climates. 8. Mollisols – these are dark soils with a lot of organic material. The soil provides a rich base so it is very fertile soil. 9. Oxisols – these are tropical and subtropical soils that are very weathered and stable. They have naturally low amounts of fertility and do not retain fertilizers well. 10. Spodosols – these are weathered soils where organic material and aluminum are stripped out into the subsoil so the soil itself isn't very fertile. The soil is very acidic. 11. Ultisols – these are soils in humid parts of the world that are also acidic with just a few inches of nutrient-rich soil. They do not retain fertilizers well. 12. Vertisols – this has a lot of clay in it that expands with moisture. These do not transmit water easily so they don't leech and are naturally fertile soils.

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BASIC SOIL TYPES There are some basic soil features you should understand. Don't worry; there are just a few of these to remember. Sandy soil is warmer and dryer than most soils. It is often acidic and too low in nutrients to grow things easily. The best part about sandy soil is that it drains well and is light when you work with it. Because it is hot, it will dry out faster than other soils. You can beef up the nutrient content by adding organic material to it. Clay soil is high in nutrients and heavy it stays wet and cold during wintertime but dries out in the summertime. Clay holds a lot of water that drains slowly. It is hard on gardeners because it can crack in the summer and doesn't warm up very fast. Silt soil is light in color and retains moisture with a great deal of fertility. It has a mixture of well-draining and moisture-holding materials. The downside is that it will wash away more easily if it is rained on. You can make it more fertile by adding organic material to get more clumps that will not wash away as easily. Peat soil is very high in organic material. It also retains moisture well. It is rarely found natively in any garden, but can be added to a garden, or created with a composting bin. It is extremely fertile for planting. Chalk soil may be heavy or light; the calcium carbonate makes it an alkaline soil. These are too alkaline for certain plants but not for others. You can acidify chalky soil except if you see too many white lumps in it; these cannot be acidified. Loam soil is a combination of sand, silt, and clay-type soil to make it fertile and easy to drain. You can refine them to have a greater combination of any of these three things, depending on what you are looking for.

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ORE DEPOSITS AND WEATHERING Rock weathering can concentrate certain minerals in soil that was oxidized from weatherized rocks. This is cool because you can find clusters of metals, regoliths or laterites, soils that have had this happen. Aluminum oxides and nickel oxides can become concentrated, but only if other metals have been washed away. Bauxite is found in tropical areas and is high in aluminum. This is where most of the aluminum in the world comes from. Nickel laterite can be found in the same types of environments. Weathering can remove the sulfur from sulfur mines. Many metals are in the ground as metal sulfides. If you wash the sulfur out, you get the metals out of the ground in more usable ways. This means that nature does most of the work in making these usable. Iron pyrite is essentially iron sulfide. If you expose it to light and water, the sulfide part goes away and you get rust plus a sulfate. The water left behind is more acidic so it more readily leaches metals out of the rock. Weathered pyrite by itself is not useful economically but if you weather it, you get gossans, which are orange or red-stained rocks on exposed rock surfaces. Gossans aren't useful either but they can herald spots where more valuable mineral ores are located. Acidic streams are also clues to the presence of something potentially valuable. Gold and copper are mined when the sulfides are stripped away in weathered rocky areas. Silver, zinc, and lead are cheaper to refine when they come out of the ground as sulfides rather than oxides. Now you see how complicated it can be to find these natural resources and why geology can help you do this more efficiently.

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KEY POINTS IN THIS CHAPTER •

Weathering can be mechanical or chemical. Most weathering is actually chemical in nature.

•

Acidic water tends to support more weathering than alkalinic water.

•

Temperature, climate, time, acidity, and topography all factor into weathering rates.

•

Soils are what lie upon the bedrock and are the parts of earth that support nutrients and water needed to grow things.

•

There are taxonomic orders used to define the different soils.

•

You should know the difference between sandy, clay, silt, loam, peat, and clay soils and what works for which types of growing.

•

Weathering can concentrate ores that can then be mined more economically in different parts of the world.

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CHAPTER 8: QUESTIONS AND ANSWERS 1.

What is not necessary to have the ice cause weathering? A. Cracks in the rocks B. A spell of cold weather C. A spell of warm weather D. A dry spell in the weather

What is the origin of a rhizolith in a rock? A. Volcanic activity B. Salt C. Trees D. Earthworms

When it comes to chemical weathering, which mineral will chemically weather first and more completely? A. Pyroxene B. Quartz C. Olivine D. Amphibole

What causes Karst topography? A. High winds B. High temperatures C. Mechanical weathering differences D. Chemical weathering differences

What is a major feature of Andisols? A. It is a type of soil you see in the desert. B. It is soil that comes from fresh volcanic activity. C. It is soil that contains no nitrogen. D. It is soil that is mostly clay.

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Soil is divided into different layers. Which of these layers or horizons is the top layer? A. O horizon B. B horizon C. C horizon D. R horizon

When you look at the different soil orders, some are fertile and others aren't. Which soil would not be at all fertile? A. Andisols B. Mollisols C. Spodosols D. Vertisols

Which soil is generally too heavy to drain very well? A. Loam B. Sandy C. Silt D. Clay

What mineral is mostly gotten from bauxite mined in parts of the world? A. Copper B. Iron C. Aluminum D. Lead

10.

What substance must get leached out of iron pyrite to make it much more able to get the iron out of it? A. Carbonate B. Acid C. Nitrate D. Sulfate

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CHAPTER 9: SEDIMENTS AND SEDIMENTARY ROCKS This chapter allows you to learn about sedimentary rocks. If igneous rocks are basically the primary rocks, then sedimentary rocks are secondary. These are the rocks that start out as smaller pieces called sediments, becoming lithified to form their own kind of stone. You'll learn how to name sedimentary rocks and what we gain economically from products these types of rocks provide us on earth.

HOW SEDIMENT FORMS You need to think of sedimentary rock formation in terms of the many stages it takes to get there. It starts with rocks that can be of any of the three known types. Then you get weathering that can be mechanical or chemical in nature. This gives you a wide variety of sediments. We will soon talk about what makes a sediment. Sediment usually gets transported and sorted. Some will get reshaped to be rounder than they were. As they get deposited, they become compacted and cemented into the different types of sedimentary rock. These lithify into rocks that are hard to separate. Remember that weathering is any combination of mechanical and chemical weathering. Mechanical processes include roots, frost, sand-basting, and water-related processes. Chemical weathering changes one type of rock into another chemically. Some chemical processes dissolve a rock entirely, while others undergo hydrolysis or oxidation in order to change the rock type. Complete weathering creates sand and clays as solid substances. It also creates soluble silica ions and metal cations that can reconfigure themselves. These are the only things considered completely weathered. Rock fragments are incompletely weathered pieces of sediment. Quartz is most resistant to weathering because of its lack of cleavage and hardness. It is the main abrasive agent when it comes to blowing sand in the desert. Water is the main transport mechanism of sedimentation. Water can be carried in rivers or streams; even larger boulders can travel this way. Dissolved minerals also get

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transported using moving water. Groundwater is good for ions, but not as good for solids. Wind and glaciers will be good transporters of solid sediment. Transport sorts out particles by their velocity and helps to round the sediment. At some point, the energy put into transportation of sediment runs out. Only so much energy is in a stream. After a heavy rain, more energy will be in the stream than you'll see in times when the stream has less water in it. Large sediments are more likely to get deposited near the source of their origin than smaller sediments. Usually, sediments that are alike in size will get deposited together. All layers get deposited horizontally as you already know. Sorting tends to separate the suspended sediments. Finer sediments stay in suspension longer and will end up further out from a river mouth or beach. Clay is seen in deeper water, while sand is seen along the beach. Ions will crystallize if the concentration gets high enough to supersaturate them, such as with evaporation. Halite (which is table salt) and gypsum (which is calcium sulfate) are both made this way. Seas and certain salty lakes will have this issue. As sediments get deposited, they get packed down so that there is no space for water anymore. There are dissolved minerals that then crystallize out from the preexisting water to cement the rest of the sediments. Silica, hematite, and calcite are all good cementers used to make rock from sediment.

SEDIMENTARY ROCK BASICS You should know the terminology regarding sedimentary rocks. The material that gets washed off during erosion is called detritus. These can be large or small and can only get transported if enough energy is involved. As the energy drops, the detritus becomes sediment. This ordinary type of sedimentation is known as clastic sedimentation. Material that gets dissolved in water and then precipitates out is called chemical sediment, or chemical sedimentation. Then you've got biochemical sedimentation, where seashells and bones are dissolved and then precipitate out. Lastly, you have organic sediment, which is the stuff in plants and animals that form fossils over time or become decomposed enough to be the gunk that coal is made from. 138

Clastic sedimentation is the type we just talked about, where there is weathering, erosion, transportation, deposition, and finally lithification. Clastic sediment has a wide range of sizes. The different sizes go from clay, which is 1/256th of a millimeter, to boulders, which are larger than 256 mm or 10 inches in diameter. In decreasing size, you have boulders, cobble, pebble, sand, silt, and then clay. If you consolidate the different kinds of sediments, you'll get various kinds of rocks out of them. Conglomerate or breccia comes from things that are pebbles or bigger. Sand makes sandstone and silt makes siltstone. Clay makes mudstone, shale, or claystone.

NAMING SEDIMENTARY ROCKS As we learn to name sedimentary rocks in this section, keep in mind that the size matters and the way the sediment came together matters. Starting with clastic rocks, you get these: •

Shale – this is dark-gray rock made from clay. You can't see these without a strong microscope.

•

Siltstone – the pieces here are easier to see with a microscope. Notice the erosion of these rocks as siltstone in figure 37:

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Figure 37.

•

Mudrocks are a lot of silt and clay that have layered out over time. Shale is a finer type of mudrock compared to siltstone; shale has the finest sediment, which is why it is so fragmental. Mudstone is a type of shale that does not break up. If shale is very organic, this is where petroleum products come from.

•

Sandstone – this has visible grains at up to 2 millimeters in size. There are fine, very fine, coarse, medium, and very coarse sand grains. A sandstone called quartz arenite is about 100% quartz, while arkose is high in feldspar. Lithic sandstone is

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high in rock fragments, while Wacke is a type of sandstone with at least 15% mud in it. Arkose is easily recognized as the pink sandstone seen in figure 38:

Figure 38.

•

Conglomerates —these are very poorly sorted and can have stone and sand in the same conglomerate rock. If you see that the gravel pieces are not rounded, you'd call it breccia.

•

Carbonate rocks —these are all based on the CO3 molecule. Some directly precipitate out, while others are made from corals and mollusks. As calcite is precipitated out along with other calcium salts, you will get limestone. After burial, calcite will become dolomite, which is a combination of magnesium, calcium, and carbonate. Dolomite doesn't fizz when mixed with hydrochloric acid, while calcite will do this.

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•

Coal —this is a biological rock made from decaying plants that build up faster than they can be completely decayed. As the layers get compacted, the partially decayed stuff becomes coal.

•

Halite, gypsum, anhydrite, and certain limestones are all precipitate types of sedimentary rock. Layers of these are known as evaporites. Even though some are mostly dissolvable in water, they become crystallized as rock and are layered to become sedimentary rock. The different chemical sedimentary rocks are travertine, which is just precipitated limestone. Dolostone is the same but has much more magnesium in it.

DETRITAL SEDIMENTARY ROCKS When you look at a clastic rock, you can say a lot about its deposition. If the particles are large, the transportation was largely very short. The opposite is true of fine-grained rocks. You also need to look at the difference in sizes. Is it chaotic or uniform? This tells you how the particles were sorted and the energy needed to do the sorting. High energy leads to larger fragments; low energy leads to sorting due to the density of the sediment. This means that both size and density affect the sorting. Some examples involve water and wind sorting. Wind sorting is usually even and wellsorted; beach-related sorting is also even because of the high energy involved. Streams are not well-sorted because the energy is so variable. Rounding happens due to abrasion. Look at the degree of rounding. If you see a lot of rounding, you can assume that a rock has undergone a lot of transportation cycles, or that there was a lot of abrasion involved. Sediment maturity also matters. This means how long a piece of sediment has been in the sedimentary cycle overall. Mature sediment is much more well-rounded than less mature sediment. Sorting that is even also indicates a greater maturity of the sediment. As sediment is transported further and further, those with unstable minerals like olivine and plagioclase become less and less. More stability in mineral content means a more mature sediment. Beaches have mature sediment mostly made of quartz. This quartz has been around for a while to get to that point. 142

NON-CLASTIC ROCKS These are based on living things and include organic or biochemical sedimentary rocks. You should be able to recognize limestone, made from calcite and perhaps see biochemical chert, which are silica pieces coming from diatoms or Radiolaria in the ocean. You might see these layered out in some way. The White Cliffs of Dover are made from diatomite, which is made out of layered diatoms. See them in figure 39:

Figure 39

Other major rocks containing chemical cherts are essentially mineralized silica where water has flowed through. Those you might be familiar with are these: •

Flint –this is gray or black due to organic matter.

•

Jasper –this is red or yellow due to precipitated iron oxides. There are many kinds of these.

•

Agate –this is silica also but with different impurities laid out in concentric rings.

•

Petrified wood –this is wood grain in color but is essentially silica.

•

Chalcedony –this tends to be white or purple and is also made from silica.

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HOW SEDIMENTARY ROCKS ARE STRUCTURED When you look at a sedimentary rock, look for the way it is layered. You can get different patterns of stratification or bedding in these rocks. Different layers can be a different color, grain size, or chemical composition. Look for rhythmic layering, where you see an alternating pattern because of seasonal changes in deposition. Lake deposits will vary in the summer and winter months. A varve is a pattern of lake deposition seen in a single year's time. You will see these layered out evenly. Other patterns you will see include cross-bedding, which involves a series of beds sitting at an incline to other beds. Beaches, rivers, and sand dunes all have cross bedding features, especially in areas that have erosion. Graded bedding involves changes in velocity of current in a river so that grain size will decrease as you go up the riverbed. If you see multiple sequences of these, they are called turbidities, reflecting a series of changes over time. Sediment can be completely unsorted or you might see sediment affected by ripples where wave action has occurred. Cracks in mud will expose surface within the cracks; this fills in with sediment that can look interesting. Other things you'll see is sediment left within raindrops or in troughs called flutes. Sedimentary rock will often be colored based on impurities or other things within the sediment. Iron oxide makes the sediment red and indicates sediment that did not form in a marine environment. Sulfides get buried along with organic material to give rock a dark coloration.

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SEDIMENTARY ROCKS AND PAST LIFE FORMS You already know that fossils will form almost always in sedimentary rock. This is because of the low temperatures involved. The pressure is low enough as well to maintain the soft bodies of small animals. Mud and sand will all be good fossil sources. Shale is a good source of marine fossils because it preserves things well. Expect to see coral, clams, algae, brachiopods, crinoids, and Bryozoa in all types of sedimentary rock. Fewer details are seen in sandstone but you will see brachiopods, trilobites, crustaceans, and Bryozoans at times. The only things you'll see well in conglomerate stones are gastropods, sponges, and some brachiopods. Rarely, you'll see igneous fossils that may have been buried by volcanic ash.

RESOURCES WE GET FROM SEDIMENTARY ROCKS Minerals dissolve at different rates. Calcite dissolves easily, followed by olivine, plagioclase, and muscovite mica. Quartz does not dissolve well at all, taking 34 million years to dissolve a one millimeter sphere. Because of difference in dissolution of rock mineral, you get new minerals concentrated out of old ones, just as mentioned in the last chapter. Now you can see how sedimentary rocks can become minable rock. Gibbsite and boehmite are both more refined forms of bauxite that are high in aluminum content. Garnierite helps to mine nickel from ultramafic rock. These are green rocks from high nickel content. Hematite and goethite are both high in iron. Clay is mined to make ceramics, paper, and sometimes cat litter. Gold collects in clastic sediments but is so dense that it sorts with larger pieces of detritus. In streams where gold could be found, you need to look not in the fine sediment in a creek but where fine sediment mixes with the larger pieces in what are called gravel bars. Conglomerate rocks from these gravel bars will also contain gold. Gold only comes from igneous rock. If you are looking for a stream that has gold in it, you should look for sediment that eroded from granite or other igneous rocky areas.

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The uses for silica are vast. You have need for silicon chips, fiberoptic cables, and other things from silicates. We mine evaporite deposits like salt out of halite. All kinds of salt are possible, including the salt in Epsom salts, potassium salts, and others.

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KEY POINTS IN THIS CHAPTER •

Sediment ranges from boulders down to clay in size.

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Water and wind are players in the transport of sediment.

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Sediment sorts by the size and density of the detritus.

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Clastic sedimentary rocks come from detritus of different sorts.

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Non-clastic sedimentary rocks come from biochemical chert, biochemical processes, and chemical sedimentation processes.

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The names of sedimentary rocks depend on the type of sediment. The size and sorting of the sediment count in defining the rock.

•

There are many things that we get from sedimentary rock.

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CHAPTER 9: QUESTIONS AND ANSWERS 1.

What is not true of sedimentation rock building processes? A. Most sedimentary rocks are formed where they are weathered. B. Sedimentary rocks can come from any other rock type. C. The end result of sedimentary processes is called lithification. D. Sedimentation processes include weathering.

What is not a type of fully weathered item in geology? A. Sand B. Clay C. Silica ions D. Pebbles

Which substance is not a good cementer when it comes to making sedimentary rock? A. Hematite B. Halite C. Calcite D. Silica

When you see the steps of weathering, transportation, deposition, and lithification as part of a rock's formation, what type of sedimentary rock is it? A. Clastic B. Chemical C. Biochemical D. Organic

Which type of sedimentary rock is not very well-sorted in general? A. Conglomerate B. Sandstone C. Siltstone D. Shale 148

What is a calcium, magnesium, and carbonate sedimentary rock called? A. Calcite B. Limestone C. Breccia D. Dolomite

Which sedimentary rock contains the finest of sediments and doesn't break up very easily? A. Siltstone B. Mudstone C. Shale D. Sandstone

What type of sedimentary rock does petroleum come from? A. Siltstone B. Mudstone C. Sandstone D. Shale

Minerals all dissolve at different rates. Which mineral would dissolve the fastest in water? A. Olivine B. Feldspar C. Quartz D. Calcite

10.

What will you try to find that indicates a source of nickel? A. Bauxite B. Goethite C. Garnierite D. Hematite

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CHAPTER 10: METAMORPHIC ROCKS IN DETAIL This chapter rounds out the discussion of rock types by revealing how we get metamorphic rock. Things, pressure, and heat cause metamorphic change in rocks, leading to many different rock types. You will understand the complexities of metamorphism and how they lead to several types of new rock from old rock.

HOW METAMORPHISM WORKS Metamorphism means change. You take a rock and add time, pressure, and heat, you will get change in the rock. There are other factors besides these and you don't need all of these except for maybe time to get a rock to change. How does change happen? It turns out that there are four different types of metamorphism that can occur. Let's take a look: •

Contact metamorphism –this is when intense heat from magma changes the minerals in nearby rocks. It involves direct contact with the hot magma. You might also call it thermal metamorphism because it involves heat. You will see this most near volcanoes and where dykes have crept up through them. This is how limestone becomes marble. Both the depth and temperature of the magma are important in determining what happens.

•

Regional metamorphism –this is where rocks change in a very large area. Pressure is a large part of this phenomenon, also known as dynamic metamorphism or static metamorphism. Temperature will also be a minor factor. The sedimentary rocks will fold because of compression on the rocks. Rocks will crystallize or recrystallize, if already crystallized. Mountains will have this feature because of the pressures put on these rocks by tectonic activity; this is dynamic metamorphism. It will be called static metamorphism if the rocks change deeply beneath the earth, simply due to pressure from the weight of rock above them.

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•

Hydro-metamorphism –this means that rock changes due to the action of water through country rocks, changing the rock chemistry. Water in large reservoirs is heavy and will also impact rocks, simply because of the weight on them. Hydrostatic metamorphism is less about chemistry and more about the weight of water.

•

Hydrothermal Metamorphism – this is a phenomenon impose by a combination of water weight plus hot gases in the region so both pressure and temperature play a role in the rocks' changes.

Figure 40 describes the different metamorphic circumstances or environments in more visual ways:

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Figure 40.

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METAMORPHIC TEXTURES If a rock isn't a typical igneous rock, or isn’t a typical sedimentary rock, then it must be a metamorphic rock. There are different categories of metamorphic rocks, including these:

FOLIATED METAMORPHIC ROCKS Foliated rocks have some type of parallel arrangement of the grains, or layers due to high pressure on the rock that squeezes out the layers so they are flatter or striped. SLATE

Figure 41.

Slate is one of these. Slate comes from shale, but it can come from other rocks termed "argillaceous" because the sediment is fine. Fine sandstone can be argillaceous as well. Look for splitting planes like you see in shale but notice that the splitting planes are not 153

the way they are supposed to be. They aren't parallel to the normal bedding planes. Figure 41 shows what mountain shale looks like: This is due to pressure on the shale that compresses the rock in mountainous regions There is pressure that can be so great that you will get phyllites, which is fine-grained mica or schist. Schist is any medium-grade metamorphic rock that comes from shale or mudstone, usually muscovite or biotite mica. There are various colors to these products but gray is typical. Slate is made from fine mica, chlorite, and many other miscellaneous microscopic grains of rock. You can split it into sheets because of its layering. Both clay and shales will make slate. As slate gets acted on further, you can recrystallize everything into larger micas and rocks called phyllites. Phyllites will go on to make schists with further changes. It is used for paving and roofing as well as other construction projects. GNEISS Gneiss is another type of metamorphic rock that is made of coarse grains. These are made from either conglomerates or granite. Expect to see a lot of feldspar in these rocks. These are foliated as well. The foliation is not as easy to see in some of these rocks. Banded gneisses can become granified, which means that it started with micaschist and ended up with gneiss. Figure 42 is what gneiss looks like:

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Figure 42.

Gneiss has the coarsest grains, which makes the banding easier to see at times. Many layers are of contrasting colors, which adds to how interesting they are. Again, with high feldspar and quartz content, these can be very interesting to see. Dark parts include amphibole and pyroxene. There are many varieties of gneiss, including these: •

Orthogneiss comes from the metamorphosis of granite or other igneous rocks.

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Paragneiss comes from the metamorphosis of sandstone and similar rocks.

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Banded gneiss comes when more flaky minerals have conspicuous banding patterns.

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Augen gneiss comes from granite plus sedimentary rocks exposed to dynamic metamorphism.

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•

Injection gneiss is that which is banded and of mixed origin. The bands alternate igneous and sedimentary rock together in alternating patterns.

Gneisses come from all over and are made from parent rocks of igneous and sedimentary origin. These are used to make buildings and for roadstones because they look similar to granite except for their metamorphism. PHYLLITE This is medium or fine-grained rock made of silica in different configurations. You might see muscovite mica in it. This is foliated and intermediate in terms of the transition between slate and schist. The presence of white or muscovite mica in great amounts will clue you in that this might be phyllite rock. The crystals might be so small you can't see them with the naked eye, but a magnifying glass will help you identify them. HORNFELS+ These are metamorphic rocks that happen where there is contact between heat and igneous rocks underground. The end result is rock that is medium or fine grained with what is called a maculose or "spotted" structure. While the granules in the rock are spotted, the whole rock will be banded or layered in some way. Figure 43 shows this banding nicely:

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Figure 43.

SCHIST Schist is more fine-grained with a lot of foliation. Schist essentially means split in German. Shale is the preexisting rock that then gets folded and compressed to become mica. When you see the shiny mica fragments, you can expect this to be schist. The rest of the rock often comes from shale so it will be relatively dark gray in color. Other schists come from hornblende and quartz. Schist has much larger granules and you will see the parallel layers fairly well. These greatly vary with regard to their color and texture. You would call a rock having a schistose structure if it has a schist-like appearance. Look for lines and micas of both kinds; there are many other minerals possible, including hornblende and chlorite. Mica schist is extremely common, having fine sediment made from plagioclase, biotite, muscovite mica, and occasionally garnet. Others, like hornblende schists, come from basalt with quartz, plagioclase, and hornblende in them. Figure 44 is mica schist:

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Figure 44.

Two groups of schists can be seen. Low grade schists involve low temperatures leading to minerals like muscovite, chlorite, and albite. These are unstable at higher temperatures. Mica-schist is a good example of this. High-grade schists come from mineral-rich areas to give rise to stable minerals like garnet, andalusite, and cordierite. Cordierite is purple or lavender and looks like this image in figure 45:

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Figure 45.

There are greenish schists that are made from chlorites and hornblende – both of which are green. If you don't see a lot of foliation you would call it a greenstone. Greenstone is sometimes mixed with an iron oxide stone to make a heliotrope stone or bloodstone. True greenstone is metamorphic rock made from igneous rocks. You might see them in ancient statues, jewelry, and tools. It is what you'd call jade, jadeite, or greenschist, among other things. Epidote, hornblende, and chlorite all color these stones green.

NON-FOLIATED METAMORPHIC ROCKS These rocks will not have any foliation or layering. There are a number of these types of rocks. QUARTZITE Quartzites are made from sandstone that was originally high in quartz. There is pressure involved that compacts the sandstone that will further compress with heat to make these

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hard quartzite rocks. They do not erode easily. They can crush shale and limestone if they lie above them, forming large escarpments along riverbeds. Quartzite is quartz upon quartz, or basically quartz crystals that are cemented by other quartz molecules. There is also orthoquartzite, which is similar but has a different type of cementing agent. Paraquartzite is quartz grains sutured so securely that they fracture in unique ways – usually along the planes of the crystals. Quartzite is hard but fractures in ways that can be dangerous to the person trying to fracture it. Fuchsite quartz is green due to chromium in the quartz. You might also see quartzite whenever sandstone-like rocks are cemented together with previously dissolved silica. These are not as hard as real quartzite and will break down into soils that are high in silica. MARBLE Marble is the result of limestone having had heat applied to it. Thermal contact during volcanic eruptions or other volcanic activity creates this marble. You can also get regional limestone dynamically as the calcium carbonate becomes calcite. You then get a new kind of mineral called calcium silicate and wollastonite. Wollastonite is a calcium silicate used to make paints, brake pads, and other things that depend on the bright color of this stone. The chemical formula for marble is calcium carbonate or calcite. It has a variety of textures and can be fine or coarse-grained in nature. Look for some banding in certain pieces of marble. While this is recrystallized calcite, it also has other substances in it, including garnet, serpentine, and olivine, which leads to its interesting coloration at times. Chalk and dolomites will turn to marble as well but you won't see as many of these. All types of marble resist erosion and are used for a variety of major building projects and statues. The Taj Mahal is made almost entirely of marble.

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CONDITIONS OF METAMORPHISM Metamorphism is something you can't see happening and it takes millions of years to accomplish anything when it comes to rock. Granite is extremely hard, so it won't change much. It is what's called an acid igneous rock, which will deform only if conditions are extreme. The quartz can flatten out and become more elongated. You might also see this in gabbro. When such rocks are crushed like this, you call these mylonites. You need a lot of heat to get contact metamorphism of granite but when it happens, you will have a lot of obvious changes in the crystals. If too much heat is applied on top of pressure, the granite will completely recrystallize into gneiss. Basic or alkaline igneous rocks like gabbro and dolerites will also change under regional dynamic metamorphism that involves heat. You will also get crushing and recrystallization of the original rock's constituents. This will lead to many different types of gneisses and schists. Hornblende is one of these end-product rocks as is a rock called amphibolite. Sedimentary rocks that are argillaceous have fine grains like clay, feldspar, mica, and quartz. Shales and other types of clays undergo contact metamorphism or heat application to make all sorts of rocks simply due to recrystallization. Heat is more likely to lead to recrystallization than pressure. Hornstone is extremely hard rock made from baking shale to the point of hardness without any recrystallization. Hornstone was used to make arrowheads. Hornstone chert is common in rocks. If shale is very high in silica, it is called argillaceous. They get crystalized under metamorphic conditions to make a rock called novaculite. It is very hard and white; you can use it for flint napping just like hornstone. Slate itself involves a great deal of pressure and heat to be made out of shale. Finally, you have arenaceous rocks, which are sedimentary but have the most silica in them. Sandstone is arenaceous because of its extremely high silica content. Squeeze that with pressure or add heat and you get quartzite as we just talked about. If the sandstone is not pure, you get odd schistose rocks instead of something closer to quartzite.

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Limestone is tricky when it changes. If it is completely pure and undergoes contact metamorphism, you get nice white marble. If there are impurities, other reactions will occur. Silica as a contaminant leads to wollastonite, which has calcium silicate in it. Aluminum as a contaminant will lead to anorthite in the rock, which is calcium aluminum silicate. Finally, dolomite, which is a calcium magnesium carbonate, provides a metamorphic rock that has pure calcite or calcium carbonate in it but also has periclase, which is magnesium oxide. Mix this with silica and then you get calcite and magnesium silicate, which is called forsterite.

METAMORPHIC ENVIRONMENTS You need to understand that the temperature and pressure will vary with location and circumstances for any rock undergoing a metamorphic change. There will be a magic combination of these that will create the different things you see. Geologists have created a pressure temperature grid that shows the relationship between different pressures and temperatures involved in changing rock. This is called the P-T diagram. It looks complicated but it provides a range of temperatures and pressures necessary to create the different rock types. A geologist named George Barrow lived in the 1800s and mapped out regional metamorphic zones and designed the Barrovian sequence that named rocks in order of increasing metamorphism. It starts with the chemical chlorite seen in slates and phyllites. Then it goes to biotite, also seen in phyllites but also in schists. Next is garnet, seen only in schists. The ones with higher grades of metamorphism are staurolite and kyanite, seen in schists. The highest grade is called sillimanite, seen in schists and gneisses. This fits well with where he lived in Scotland. Green coloration or greenschist rocks are seen in low pressure and temperature situations. Chlorite, epidote, and serpentine are all green so the schist will be green. These rocks are called schists because there is muscovite mica in them. There are many environments that nuance the rock types coming out of metamorphism. We talked about some of these in the beginning but now that you know these rocks 162

better, you should be able to see what happens with greater clarity. These are a few examples of environments you will see having metamorphism of different types: •

Burial metamorphism – this is an environment where rocks are deep within the earth. Sedimentary rocks often get buried below other sediment so that clay becomes a mineral known as illite. Sandstone becomes quartzite under such high pressure situations.

•

Contact metamorphism – you remember this as being more heat-related than pressure-related. You will get different things, depending on how much pressure is added. Hornfels comes with low pressure but if you add pressure, you can get amphibolite, greenschist, or granulite. The parent rock matters too. If you start with basaltic rock like shale, you'll get hornfels, but if you start with sandstone, you'll get quartzite. Limestone, as you know, becomes marble.

•

Regional metamorphism – this you remember is when pressure and temperature both act over larger areas. Mountain ranges are good spots for this because continental crusts are converging. Obviously, this will vary over time and distance from the converging plates. Sediment becomes slate that becomes phyllite, schist, gneiss, migmatite, and then granite. This is the sequence to remember when it comes to regional pressure and temperature variations in continental plate convergent zones.

•

Subduction zone metamorphism – this is also regional but occurs in subduction regions. The descending crust has an increasing temperature as it sinks, but the pressure factor is greater than the temperature factor. Blueschist is a common rock that comes out of this; it contains a blue mineral called glaucophane. Figure 46 is what this blueschist glaucophane looks like:

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Figure 46.

These conditions also create epidote, almandine, chlorite, garnet, and jadeite. These are all metamorphic rocks occurring when pressure exceeds temperature in subduction areas. Very deep areas where pressure and temperature are the greatest lead to shearing of the minerals; this gives rise to things like tiger's eye. •

Shock metamorphism – these are rare circumstances you'll get when a meteorite hits earth. The pressure is very high and delivered quickly so you get interesting things like shatter cones and unusual things representing the shattering and deforming of crystals. Glassy material is a common complication of shock metamorphism. Tektites are interesting pieces of glass ejected after an impact. They look like volcanic glass but are chemically different. They also are round and look like large pebbles. Rapid heating and cooling are the things necessary to make glassy objects in geology.

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KEY POINTS IN THIS CHAPTER •

Metamorphism involves heat and pressure; contact metamorphism implies heat, while dynamic metamorphism implies pressure added.

•

The parent compound matters, so if you start with sandstone, you'll get a different end product than if you start with clay.

•

Some metamorphic rocks are foliated, while others are non-foliated. Non-foliated rocks are quartzite and marble, while foliated rocks include gneiss, schist, slate, and others.

•

There are large regional differences depending on the presence of things like convergent plate activity or subduction activity.

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CHAPTER 10: QUESTIONS AND ANSWERS 1.

When you have contact metamorphism, what most changes the affected rock? A. Erosion B. Pressure C. Temperature D. Chemical change

What factor most causes static metamorphism? A. High temperatures B. The weight of overlying rocks C. Plate tectonics D. layering of rock

What common feature will you often see with schist? A. Flakes of mica B. Pink feldspar granules C. Large quartz grains D. Stark black coloration

What rock does quartzite come from? A. Mudstone B. Shale C. Sandstone D. Quartz

What is the trend toward adding pressure to clay look like? A. Clay to schist to phyllite to slate B. Clay to phyllite to marble C. Clay to slate to phyllite to schist D. Clay to phyllite to schist to slate

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Which is not a low-grade type of schist? A. Mica B. Garnet C. Chlorite D. lbite

What is the chemical formula of marble? A. Potassium chloride B. Sodium carbonate C. Calcium sulfate D. Calcium carbonate

What will tell you that granite has undergone metamorphism in some way? A. The quartz crystals are flattened. B. The rock becomes more mafic. C. The rock will be neatly layered. D. The rock will recrystallize into pure quartz

Which type of metamorphic rock is not unique to subduction zones? A. Epidote B. Quartzite C. Chlorite D. Glaucophane

10.

Which phenomena lead to the formation of glassy tektites? A. Shock metamorphism B. Subduction zone metamorphism C. Convergent zone metamorphism D. Burial metamorphism

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CHAPTER 11: EARTHQUAKES AND SEISMOLOGY This chapter is about earthquakes. Studying earthquakes reminds us that geology isn't just about rocks. Earthquakes are perhaps the best proof that plate tectonics is not theoretical. They happen mainly when two or more plates are moving in directions that are not congruent with one another. You will learn how earthquakes are measured and see why they cause so much damage.

EARTHQUAKE DEFINITION Earthquakes are essentially sudden slippages of plates along a fault line. The plates are always moving but they get stuck due to friction. Once the pressure to move the plates is greater than the friction holding them back, you will get an earthquake due to sudden movement. Energy is released into the ground and dissipates, leading to the movement you feel in an earthquake. An example of a Faultline is the San Andreas fault. It is about 650 miles long and up to 10 miles deep. There are other fault lines that converge into it along this zone. Together, these are places where the pacific plate and the North American Plate connect and ride in a transform plate boundary. Figure 47 shows you where this fault lies:

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Figure 47.

Along faults like this, there will be many shocks a person doesn't feel. Often these are a good sign because they indicate little friction. If you don't see these happen regularly, the stress can build up for hundreds of years, which is short in geologic time but enough

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to cause a giant jolt when the friction releases. This is when you'll feel the largest earthquakes. A few definitions to help you understand earthquakes better are in order here. First, is the "fault" or fault plane. You can also call it a fault line, even though it goes deep within the earth. This is the place where slippage between two plates occurs. Remember, you can have major plates, minor plates, or microplates involved in this slippage. The hypocenter is where the earthquake begins below the earth's surface; the epicenter is the same spot on earth just above the hypocenter. A foreshock is a smaller earthquake that likely heralds a larger one in the same area. The mainshock is the "big one", the largest of the earthquakes. Aftershocks always follow the mainshock and can be strong; they will always be in the same place as the mainshock. Expect aftershocks up to years after the big one. Remember that the crust is just a thin skin around earth compared to the mantle, outer core, and inner core. The crust is not confluent but is made of plates that float round with some degree of interdependence on one another. The plate boundaries are where all the action is and where the fault planes exist. None of the plates has a smooth edge so as they slide past one another, there will be friction. Once the force of movement exceeds the friction between the two plates, a sudden shift occurs and an earthquake happens. The energy stored in the stuck part of the plates under friction gets released at one time. This energy is sent out as seismic waves that ripple out from the epicenter. The earth shakes when this happens and anything on the surface of the earth near these waves gets disrupted as well. We will talk more about earthquakes and their recording soon. Suffice it to say that you need a seismograph to record earth movements. It is basically a recording device that stays stationary but the earth it is on is not at all stationary. Paper gets run past the pointer at a regular time and the strength of the waves recorded get printed on the paper, called a seismogram. The device is weighted at the end of what you might call a string so it won't move much even if the earth does. The earth moves but the stylus does not. Figure 48 shows a schematic of how this works:

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Figure 48.

Scientists measure size in ways that don't necessarily reflect how much slippage there has been. This is because it can't really be measured so easily. Seismograph readings on the earth's surface will usually tell how strong the quake was. More deflection means a greater earthquake, in general. The length of the deflection reflects fault length but the size of the deflection speaks to the amount of slippage. We call the size of any earthquake the magnitude of it. This isn't the same as the intensity, which varies depending on where you happen to be located with respect to it. You will learn soon how to say where a given earthquake happened.

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EARTHQUAKE FEATURES The major feature of an earthquake is ground shaking. This comes from seismic waves passing through the earth's crust. The shaking might be mild or extreme and will vary in duration. Buildings can easily be damaged or destroyed. The shaking won't kill you; it will be the infrastructure damage to roads and buildings that will kill you. The ground can actually rupture after an earthquake. This is rarer than you'd think but when it happens, you will see fences and railways off by feet or more. Ruptures can destroy pipelines, roads, airport runways, and aqueducts that can add a lot to the damage you'll expect. A fault scarp can happen, which is a cliff or step off large enough to cause a large divot or crack in the earth. Landslides are also possible with earthquakes. If a slope is unstable or if there is a direct rupture of earth itself, there can be landslides that are deadly to things below their level. Landslides can damage the terrain if the earth blocks creeks and rivers. This problem is obviously worse in areas where there are cliffs and mountainous areas already. Tsunamis are not tidal waves but are part of earthquake phenomena. The Pacific Ocean basin is home to a great potential for these deadly events. They only occur when the slippage is vertical rather than side-to-side or strike-slip movements. This causes a mass movement of water that can travel huge distances at about 700 kilometers per hour and may reach wave heights of 90 feet or more. The water may recede before it returns in increasing waves that can travel far inland. Finally, liquefaction can occur. This is the most destructive feature of an earthquake. Sediment in the earth floats upon the underlying groundwater and then recompacts in what's called subsidence. You can get giant sand volcanoes or sand blows reaching up to damage buildings and infrastructure. Buildings can sink into the ground when this happens. Underground tanks will rise through the liquefied earth. Sand blows are not dangerous but look like cracks in the earth with large collections of sand around the vents.

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EARTHQUAKE MEASUREMENTS Measuring earthquakes is important to understanding what is happening to the earth's crust. It also helps to construct infrastructure and buildings that will withstand potential future earthquakes. There are parts of California that are basically shaking continually. Most people don't feel anything at all. Historically, the magnitude of an earthquake was only based on measurement of the seismogram. Nowadays, the magnitude is adjusted to account for the damage the earthquake does in general as well as the seismographic report. There is a worldwide network of seismographs that can say when and where there is seismic activity. The graph is digital and plotted over time. Figure 49 shows what a seismogram reading looks like:

Figure 49.

There will be background waves over time so that you won't ever see a flat line. You see these from nearby traffic or from wind activity. These are very sensitive machines after all. There are tiny dots or marks to indicate each minute. These are necessary because each seismogram is different. There are different kinds of waves, broadly categorized as body waves and surface waves. Body waves will go through the "body" of the earth. You can have P waves,

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which are primary waves, and S waves, which are secondary waves. P waves go through anything, while S waves only go through rock as these are shearing-type waves. P waves represent mild elevations above the baseline noise. The baseline squiggles you see all the time are called microseisms. P waves are still slight but they are fast and indicate a possible earthquake. Above these are the S waves, which are the largest ones you will see. No S waves can still mean that an earthquake happened but that it happened too far away on the other side of the planet. P waves can travel through the earth's liquid parts but S waves cannot. This is how you know when an earthquake was nearby or not. S waves come after P waves. Surface waves are their own kind of wave. These only travel through rock and have a slow wavelength as a result. There are two kinds of surface waves: Raleigh waves and Love waves. Love waves move side to side across the wave's direction. Raleigh waves are elliptical. They are slower than Love waves but spread out wide. You'll see these last a long time after an earthquake.

MEASURING MAGNITUDE OF AN EARTHQUAKE There is only one magnitude for any given earthquake. It is not location-dependent. The Moment Magnitude Scale has been in use since 1970 all over the world. This is different from the intensity, which as mentioned, is location-dependent. Geologists use the Modified Mercalli Scale to measure local earthquake shaking activity. Magnitude scales for earthquakes are not linear; they are logarithmic. One point increase equals ten times the strength. The Richter scale is no longer in use as it was only valid in Southern California and does not put into play all of the seismographs in the world. The MMS or moment magnitude scale is used to measure rock movement on a fault line. It is excellent for measuring the magnitude of large earthquakes. There are differences among the different magnitudes and what they mean. Within the MMS, there are classes of earthquakes called earthquake magnitude classes.

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These are simple to remember. •

Minor quakes – 3 or more but up to 3.9

•

Light quakes – 4 to 4.9

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Moderate quakes - 5 to 5.9

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Strong quakes – 6 to 6.9

•

Major quakes – 7 to 7.9

•

Great quakes – 8.0 or more

Intensity is different than magnitude and is based on what is seen on the ground after an earthquake. It looks at the environment and related things to say what the effect of the earthquake has been. It is entirely based on where you are on the planet near the quake. Remember that the MMS is an international measure of magnitude; the MM is the Modified Mercalli Scale. This measures earthquake intensity. The original Mercalli Scale was developed in 1902 and modified 29 years later to say what the intensity is of any given quake. They use Roman numerals to depict the intensity rating. An intensity of Roman numeral I is not felt by most people. Maybe a few people in tall buildings will notice the shaking. Roman numeral II is so weak that a few people feel it and some delicate things like chandeliers will sway. It is only at Roman numeral IV that car alarms go off and dishes are disturbed somewhat. By the time you get to an intensity level of Roman Numeral VIII, you get partial building collapse, chimneys falling, monuments and walls cracked, and overturning of furniture. This would be a severe earthquake intensity. Violent and extreme earthquakes are Roman Numeral IX and X, respectively. The damage is severe to foundations, while wooden and masonry structures are destroyed. Railways can be bent. Notice that intensity is based almost exclusively on damage to buildings, cars, and infrastructure. The milder intensities are based mainly on whether or not the earthquake is felt at all.

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EARTHQUAKES UNDERWATER Earthquakes underwater are also called underwater earthquakes. They generally begin at the bottom of the ocean and are the main causes of tsunamis. Their magnitude can be measured by the moment magnitude scale just as they can on land. Intensity can also be measured. They happen in the same way as land earthquakes and, as mentioned, cause tsunamis if the slippage was vertical. Because tsunamis travel far, the intensity can be large at distances far from the epicenter. Underwater communication can also be affected.

DETERMINING EARTHQUAKE LOCATIONS Seismography can help say where the epicenter of an earthquake was but you need to have more than one to have a reading of where this epicenter was located. The most basic measurement of these kinds of things involves three seismographs and a process called triangulation. You also need a map world, a pencil, a compass, and a good ruler to do this. The seismograms you read will have P and S waves on them. These are plotted over time. You will need to say how far the first P wave is from the first S wave. This will tell you precisely how far away the earthquake was from the seismogram. There are charts that will be able to do this for you. Now you just have to put the point of your compass on the map where the seismograph was and draw a circle however far apart you measured. The seismograph cannot say the direction from it that the earthquake happened. The height of the strongest p wave also says the magnitude of the earthquake; there is a graph that will tell you the absolute magnitude of the earthquake. Take three seismograph readings from three different nearby areas and do the same thing as with the first. Now you will have three circles on the map with different magnitudes and distances. The epicenter is where all three circles have an overlap. It will be just one place on the map. Figure 50 shows you how this is done:

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Figure 50.

EARTHQUAKE PREDICTIONS Earthquakes cannot be predicted and we do not know if it will ever be possible. The best that the US Geological Survey can do is calculate some type of probability that an earthquake will happen within the next few years. Foreshocks or increased activity in an area does suggest a big one is coming but it may not.

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KEY POINTS IN THIS CHAPTER •

Earthquakes happen along plate tectonic fault lines as they move in different ways.

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There are many features of earthquakes, including liquefaction, earth shaking, and ground rupture.

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Tsunamis come from underwater earthquakes with vertical slippage.

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The magnitude of an earthquake is fixed according to the Moment Magnitude Scale.

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The seismogram is a reading that can show the magnitude, time, and distance from an earthquake.

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The intensity of an earthquake is variable by location.

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Triangulation is used to find the epicenter of the earthquake.

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CHAPTER 11: QUESTIONS AND ANSWERS 1.

You live in an earthquake zone along a fault line and hear that there haven't been many small tremors in many years. What can you assume from this? A. The plates have stopped moving here. B. There is subduction going on to reduce the tremors. C. The plates are moving without friction. D. Friction is likely causing an increase in the risk of a large earthquake.

What is the most accurate description of the epicenter of an earthquake? A. It is where the earthquake starts. B. It is on the earth's surface above where the earthquake starts. C. It is the area of the greatest damage to property. D. It is the area where the earth moved to the greatest extent.

What is a good synonym for a fault scarp? A. Rumbling B. Elevation C. Liquefaction D. Crack

What aspect of an earthquake is likely to cause the most damage and destruction? A. Landslide B. Liquefaction C. Ground shaking D. Fault scarp

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What earthquake phenomenon will be most easily survived but only if you are outdoors? A. Tsunamis B. Landslides C. Liquefaction D. Ground shaking

When you read a seismogram, what does it most represent? A. Waveforms over distance covered B. Deflections of earth's crustal movement versus time C. Deflections of the magma movement versus distance beneath earth D. Vertical movement of continental crust versus oceanic crust over time

Which waves from an earthquake move the slowest? A. Microseisms B. Raleigh waves C. S waves D. Love waves

Why do we no longer use the Richter scale for measuring earthquakes? A. It was a linear scale and we needed a logarithmic scale. B. It underestimated the dollar damage of a given earthquake. C. It only worked for ground-based earthquakes. D. It was mostly only valid for Southern California earthquakes.

You measure an earthquake magnitude and get a 6.1. What is this classified as? A. Mild B. Strong C. Great D. Severe

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10.

In measuring earthquake intensity, which scale is used for this? A. Modified Mercalli scale B. Richter scale C. Mercalli Scale D. Moment Magnitude Scale

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CHAPTER 12: CRUSTAL DEFORMATION AND MOUNTAINS This chapter teaches you how and why rocks deform. Rocks seem so solid and yet the awesome powers of earth movement can create giant mountains and crush sedimentary rock into much harder metamorphic rock. You will learn the patterns of rock deformation and the types of stress the earth's crust is under on a daily basis. It will help you understand why the earth has the interesting topography it has now and why it will probably continue to have fascinating changes in its features in the future.

HOW ROCKS DEFORM There are intense pressures and forces at work in the earth's crust that are going on all the time. These forces cause rocks to bend, twist, or even fracture into pieces or dust. These changes are called deformation or deforming rock. We often use the term stress to explain these forces. Force per unit area is called pressure. There is lots of pressure in the earth going on all the time. A lot of force applied to a small area means that there is a great deal of pressure in that area. Stress is what we call pressure in geology. Uniform stress is termed pressure. It means that the force is the same wherever it is applied. When rock is compressed by overlying rock, this is called uniform stress. It is also called "confining stress" because it involves a lot of confining pressure! Differential stress implies some type of inequality in the force applied to the rock. Differential stress comes in three types: •

Extensional or tensional stress – this is force that extends or stretches rock.

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Compressional stress – this is force that squeezes the rock in differential and not uniform ways.

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•

Shear stress – this is when you get slippage or translation on rock. This is most likely to contribute to the twisting of rock in some tangible way.

Rocks deforming means they are under strain. We define strain as any change in the shape, size, or total volume on a rock. Now that you have stress and strain on rock, you can see that it will deform the rock. Rock doesn't deform in a random way. It goes through several stages of deformation as this happens. Let's look at these stages of deformation so you can see how a rock can change as force is applied to it: •

Stage 1 – this is called elastic deformation. Like any deformation, it is completely reversible if the pressure on the rock is removed.

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Stage 2 – this is called ductile deformation. The strain is irreversible by now but the rock is still intact.

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Stage 3 – this is also irreversible and happens as the rock is fractured completely.

DUCTILE VERSUS FRAGILE ROCK Of course, all rocks do not behave the same. You know intuitively that some rock is fragile and more brittle, while other rocks are stronger and perhaps more stretchy. In geology, we divide these rocks into different types based on how they behave under stress: •

Brittle rock will not be ductile enough to remain intact. It will fracture easily.

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Ductile rock will be more elastic so that it will stretch more or bend before fracturing.

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Temperature affects how ductile a rock will be. Like anything, high temperature means more ductile behavior.

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The presence of confining pressure will diminish the chances of a fracture. Low pressure around a rock will alternatively increase the chances of a fracture.

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Strain rate matters – if the rate of strain is too fast, there is a greater chance for a fracture compared to a slower strain rate.

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Rock composition matter as well – olivine, feldspars, and quartz are all more brittle than clay, calcite, and mica.

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Water presence or absence – if there is water around, the chemical bonds between atoms in a rock are looser so that there is more ductile behavior than you'll see with a drier rock.

Rocks that are closer to the surface of the earth and are higher in quartz content mean that the rock will be more brittle. These rocks, like quartz and feldspar, are strong rocks but not very ductile. Most sedimentary rocks are much more brittle than most igneous rocks and metamorphic rocks. Deep within the earth, you get to what is called the crustal brittle-ductile transition zone at 15 kilometers deep, below which the rocks are very ductile and total rock strength diminishes. The bottom of the crust has a lot of olivine in it, which is fairly strong, helping the upper mantle layer to be strong here too. Higher temperatures below the crustal areas and into the mantle of the earth, you then get to a 40 kilometer-deep area, called the mantle's brittle-ductile zone. Rocks in the mantle here are also more ductile deep to that level. Deformation of rock is such a slow process, you don't see it unless there is an earthquake. Geologists can measure deformation that is somewhat less abrupt in areas where there is change happening in subsidence areas or where there is uplift. It may take years still to succeed in detecting rock deformation. Deformation is easy to see in areas where there have been sedimentary deposits. Remember the principle of horizontality? If you do not see horizontal layers, you can assume that deformation has happened.

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STRIKE AND DIP EXPLAINED Take a look at figure 51 to understand what dip and slip are all about:

Figure 51.

Geologists use the terms strike and dip to explain rock deformation. These two terms will be perpendicular to one another all the time. You need to have a way to define what the strike and slip are like in any given area: Step 1 is to find an area where there has been an inclined plane in rock beds showing a difference from the horizontal. In the figure, you see that water is set as the true horizonal in example. Step 2 is to determine the strike. This is the compass direction of the horizontal aspect of the plane. Get out your compass to figure out which direction it is across the incline. It might be something like North 10 degrees to the East.

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Step 3 is to determine the dip. This is a perpendicular line down the face of the incline toward the water in the example. You might say it is 35 degrees West of North. Step 4 is the measure the dip angle. The dip angle is the angle of the incline compared to the horizontal. You might say it is 65 degrees angulated with respect to the horizontal.

FAULTS AND JOINTS A joint is any separation of a block of wall where there has been no movement on either side of the crack. It takes pressure from gravity or from forces behind or beneath onehalf of the joint to create a fault. A fault is a good example of what happens when brittle rock fractures or breaks. You will see an offset at this point because the two halves didn't just break and stay in place. They broke and then moved in some direction away from each other. The reference point is the inclined plane. The block below the inclined plane is called the footwall, while the one above the inclined plane is the hanging wall. The hanging wall will either fall due to gravity or rise when a force thrusts it up the plane. A geologist's goal is to describe what has happened to the two halves. Note the inclined plane aspect of the images you look at in figure 52 as you think about which fault is which. Figure 52 shows you the different fault types in better detail:

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Figure 52.

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Here is how you describe the different faults and their respective movement: •

Dip-slip faults – this is when two segments rise or dip compared to another segment. There are two types of these. In a "normal" dip-slip fault, a segment dips downward, just as you'd expect would happen because of gravity. In a reverse dip-slip or "thrust" dip-slip, a force opposite to gravity has force a section of rock to move upward in relation to another one.

•

Strike-slip faults – this is when two halves of a fault slip past one another horizontally. You need to think about these faults in terms of their relative directions. A right lateral strike-slip is when the right side slips downward as the left slips upward. If you think of a line or fault as being on a clock face, a right lateral slip has the right side facing the 6 o-clock position, while the left lateral strike slip has the right side facing the 12 o-clock position. Transform boundaries along tectonic plates are just giant strike-slip faults.

There are different patterns of faults you can encounter. Some are related to extension along two sections of rock, such as along a rift zone. A Horsts and Grabens situation is where there is tensional stress that causes faults to dip in opposite directions. There are down-dropped sections called grabens along with uplifted blocks called horsts. A rift valley is a Horsts and Grabens situation. You might see these in places like Idaho, Utah, and Nevada, where newer crustal areas have gotten extended in places, creating new valleys. Figure 53 is a Horsts and Grabens situation:

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Half-grabens are faults where a drop-down has occurred due to extension but there is no uplift on the other side. You can get series of half-Grabens where they look like dominoes in the process of falling down. These are more common than Horsts and Grabens.

ROCK FOLDING Rock folding is different than a fault line. Faults are fractured areas, whereas folding happens to ductile rocks. Compression over time leads to folding. The strain rate needs to be low so you don't get fracturing. The two sides of any fold are called limbs. Figure 54 shows some geometry you need to know with regard to geological folding:

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Figure 54.

Notice the axial plane running perpendicular to the hinge line and the two limbs on either side. A line drawn perpendicular to the axial plane is called the fold axis. The fold axis runs along the hinge line in a relatively straight way in any routine fold. The limbs will be the straightest part of the fold. The axial plane will divide the fold roughly in half as symmetrically as possible. There are three known folding patterns you will see going on. These include the following: •

Monoclines – these are simple and involved the bending upwards of horizontal layers in an upward direction so that you basically see a downward hill with strata that are uniform and parallel to one another. If you draw an imaginary line perpendicular to the limb edges, it will not be vertical but will tilt downward. This imaginary line is called the axial plane. 190

•

A syncline is a trough, where the limbs are on either side and horizontal, with a midline sinkage. The fold plane is one that divides two areas that are roughly symmetric on either side of the trough. Figure 55 shows you a syncline:

Figure 55.

•

An anticline is an arch, with two limbs on either side and a fold axis that is still straight up. It is the opposite of a syncline. The fold plane will still separate roughly in equal halves of the arch.

Variations on these are domes and basins, where the layers are dipping in the center of a basin or rising in the middle of a dome. There is not just two limbs but a ring of rock that is different from the central portion. There is no real fold axis as the hinge just comes up to a point at the center of the dome or basin. You can see where these things have happened only if there has been erosion of an area so you can see the layers. This is how you can see what's happened over time underneath the earth. The layers or strata in domes and basins will be concentric around a central point. Anticline folds get older as you get toward the central axis, while syncline folds get younger as the rock erodes toward the central plane of the fold. 191

Here are some more variations you might see: •

A plunging fold means that the fold axis is not horizontal. There is an angle to the fold axis with respect to the earth.

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A symmetrical fold means that the limbs fold away from the hinge at the same angle. If this doesn't happen, it is asymmetrical.

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You can also get a really wacky fold called an isoclinal fold, where the limbs have gotten so bent that they are parallel to one another. This would be the geological equivalent of a hairpin turn.

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If a fold falls over due to pressure on one side more than the other, it is an overfold. An overfold that is extremely folded over is called an overturned fold.

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The most extreme overturned fold is a recumbent fold, where the limbs are hairpinned back to back and the entire thing has fallen over onto its side.

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Chevron folding is zigzag folding where none of the limbs are curved.

Folds affect the topography of the land. Once weathering and erosion happen, the rock types less resistant to it will be eroded away, leaving behind more resistant layers. Now you'll get ridges where layers have resisted erosion and valleys where layers have given into erosion.

FOLDING AND MOUNTAIN BUILDING Mountains are built out of deformations of the earth's crust. Most mountains are a mixed bag of folding but you'll see certain patterns in mountain building that are created out of specific deformation trends. Three types of mountains can then be identified: •

Fault block mountains – these are made by different patterns of faults. Reverse faults or thrust faults will push up more brittle rocks into mountain ranges. Some known fault block mountains are the Sierra Nevada Mountains, the Tetons, and the Harz mountains located in Germany.

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•

Fold and thrust mountains – these are due to large compressional areas of stress so great that crusts from two tectonic plates collide. Folding and faulting happen together to make the Himalayas, the Appalachians, parts of the Alps, and the Rocky Mountains.

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Volcanic mountains – you know all about these. These are not deformational. Magma simply builds these mountains up by the bottom up. The Hawaiian Islands, Iceland, the Cascade mountains, and many others are volcanic mountains.

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KEY POINTS IN THIS CHAPTER •

Rocks are under pressure. This pressure can cause rocks to variably bend or fracture.

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Rock types range from being very ductile to being extremely bitter. Temperature and the rate of strain on a rock will determine whether a rock bends or breaks.

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Joints and faults are both cracks in rock. Joints do not move but can expand or contract, depending on the circumstances. Faults are basically joints that have moved with respect to one another.

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Remember the four variations on faults, such as the normal fault and reverse fault, which represent up and down movement. Slip-strike faults slide past one another in two possible ways.

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The dip and slip of rocks will tell you a lot about what has happened to a fracture.

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Folds are from bending rock. There are various patterns of folding inward and outward in symmetrical and asymmetrical ways. Remember that folding features are only really seen when there has been erosion of rock so you can see the layers.

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Mountain building involves fractures and faults or folding and thrusting. Volcanic mountains do not involve pressure on rock.

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CHAPTER 12: QUESTIONS AND ANSWERS 1.

In geology, the term force per unit area is also known as what? A. Work B. Velocity C. Pressure D. Voltage

When a rock changes in size or shape, what is this called? A. Strain B. Pressure C. Tension D. Compression

Which rock is more likely to fracture, simply because of its properties? A. Calcite B. Micas C. Quartz D. Clay

What factor does not increase the ductile properties of a rock? A. Higher temperature B. Faster strain rate C. Higher compression force D. Higher water content

When it comes to ductility and brittleness of a rock, what statement is true? A. Gradual application of force usually leads to fracturing. B. A ductile rock is evidenced by twisted pieces within the rock. C. A Sedimentary rock will generally be more brittle than an igneous rock. D. Sudden force application to a rock will usually lead to twisting of the rock.

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An earthquake happens where you see a fault-line. Along the fault, a section has sunk and slid down relative to another section. What do you call this fault? A. Normal dip-slip B. Reverse dip-slip C. Right lateral strike-slip D. Left lateral strike-slip

You are looking at an eroded surface of rock and see layers that have folded. The folded layers form an arch in the middle. What will you call this exposed layer, assuming it represents a ridge along the area you are viewing rather than a hill? A. Basin B. Syncline C. Monocline D. Anticline

Which type of rock folding is evidenced by a plane of folding that is not completely vertical with respect to the limb fold? A. Basin B. Syncline C. Monocline D. Trough

An extreme folding pattern in rock that looks like a hairpin that has folded horizontally with respect to the earth is called what? A. Isocline fold B. Overturned fold C. Asymmetric fold D. Recumbent fold

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10.

Which famous mountains are known as Fault Block mountains? A. Himalayans B. Appalachians C. Cascades D. Sierra Nevadas

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CHAPTER 13: EFFECTS OF GRAVITY This chapter helps you understand better the geological phenomena seen because of gravity. Gravity pulls everything toward the center of the earth so heavy things that don't have the necessary friction or infrastructure to hold up properly will fall. Rock, dirt, sediment, snow, and ice all participate in this process to create things like landslides, mudslides, flows, and even avalanches. You'll see that there are more forces at play in these gravity-based situations besides the law of gravity.

LANDSLIDES A landslide is less commonly called a landslip in geology. These are mass movements that can involve rocks, mud, sediment, or dirt. An entire slope can fail or a cliff edge can fall to create a landslide, among other options. Underwater landslides are also possible. Most landslides are triggered by something besides gravity. Rain, construction in an area, and tremors from a mild earthquake can be the trigger that causes gravity to take hold. Once the shear strength of a given area is insufficient to counter gravity, some of the slope will fall. Normal processes in geology can cause landslides, including these: •

Saturated land due to rain, snowmelt, or glacial melting

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Water creeping into rock fractures or fissures

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Raising of groundwater level suddenly from deep in the ground, such as in aquifers

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Forest fires that deplete the vegetation or soil nutrients after a prolonged fire

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Repeated freezing and thawing or repeated heating and cooling of the environment that contributes to higher weathering rates

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Slope erosion, usually by river or ocean water

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•

Earthquake activity that destabilizes or liquifies the slope

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Nearby volcanic activity

Humans play a role in landslides as well. This is a brief rundown on human contributions to landslide formation: •

Construction causing vibrations

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Heavy traffic

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Mining events

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Deforestation and crop cultivation on slopes

COMPONENTS OF A LANDSLIDE

Figure 56.

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There is some landslide terminology you should know about. Figure 56 shows a few of the features you might see after one has happened. They are labeled from "head" to "toe", so to speak. Crown cracks are seen above the landfall where the earth has been tugged by the weight of the fall before it fell. The crown is the top of the earth just above the landslide. A scarp is a cliff face; there can be a main scarp and one or more minor scarps. At the top of a minor scarp is a ledge called a head. The upper part of the fall is the zone of depletion, where rock has been removed from a spot. The bottom part is the zone of accumulation, where rock or debris has been added. You will be able to see the surface of the rupture and its main body, where the debris is missing. More debris is added to existing debris at the foot of the landfall. The very ends of the landfall you see after it has traveled are the tips of the toes, but the toes themselves are the bottom edge of the rupture itself. The surface of separation is below the rupture. Expect to see some transverse cracks from side to side as well as radial cracks that run up and down along the zone of accumulation. In between cracks, you can have buildup that forms ridges of debris near the base of the landfall.

TYPES OF LANDSLIDES Most landslides happen in more remote areas where people are not significantly affected. Landslides are not all dramatic and catastrophic. You can have various types of rapid or slow mass movement of earth. The material that falls and the mode of falling both go into the classification of a landslide. These include the following different types of phenomena: •

Slides or sliding events – these are true landslides in restrictive sense. There is usually a single weak point or weak zone that causes a separation of earth from its original elevation. Rotational slides involve a concave slope left over after the slide has happened. There is a greater slope at the top of the slide than the bottom. A translational slide is simpler, with just a fall down an inclined plane. Of

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these, the rotational slide is more spectacular, with large chunks of earth being displaced. •

Falls – these are sudden movements, usually of rocks and/or boulders that separate from cliffs or mountain slopes. Bedding planes, joints, or faults can be sources of these freely falling and bouncing rocks. These are deadly because of the numbers of boulders, their speed, and their weight. Water in the earth and mechanical weathering contribute to this kind of fall.

•

Topples – this is a pivoting or rotating of a bunch of rock due to instability and the effects of gravity. Fluid in cracks can cause chunks of a cliff to topple off their original location.

•

Flows – these are more complex and involve different types of materials and speed. These are the different flows you might encounter: o Debris flow – these are rapidly moving mixtures of rock, organic material, water, and dirt flowing downhill. They are often due to heavy rains or snowmelt and can arise after a landslide has upset the ground. Gullies are often linked to these kinds of dangerous flows. The slope generally must be more than 20 degrees to have any type of flow like this. They will continue to creep if the slope stays at 10 degrees or more, depending on how wet the debris slurry is. Most of these begin as a translational slide, leaving some rubble or debris in their wake as they are completed. Most of these are not very large. o Debris avalanche – this is just an extreme debris flow that moves very fast. It is highly dangerous. o Earthflow – we will talk more about these in a minute. These are hourglassshaped flows with fine-grained debris or clay that forms a long flow on a moderately-steep slope. o Mudflow – this is a type of earthflow where the material is very wet. There needs to be at least 50 percent fine particles like silt or clay. o Creep – these are flows that can be imperceptible at times and involves either soil, rock, or both. There is enough shear stress to have gradual movement

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without destroying the terrain completely. These may be seasonal, continuous, or progressive in nature. Progressive creeps gain momentum over time. You'll see evidence of creep if trees are bent or if there are ridges in the soil that is currently creeping. •

Lateral spreads – this is a unique type of land movement where the slope is flat or very slight. The movement of material extends out laterally due to liquefaction of very saturated earth and sediment with very little cohesion to the pieces. Earthquakes can trigger these because of ground shaking. If water is added to loose material, you can get lateral spread of this liquefied stuff in a progressive fashion, where momentum builds up over time. The failure begins small but spreads fairly quickly in a complex series of events that lead to this being called a complex landslide, depending on the circumstances.

•

Solifluction – this is due to a combination of flow and creep that falls in sheets on steeper slopes.

In a typical rock avalanche, for example, you have several factors to consider regarding its behavior and what to expect. If the initial drop was steep and fast, the runout over space does not need to involve much of a decline and could involve an uphill excursion of material. If the mass moves fast enough, friction as the mass slides will heat up the underground area. This can further reduce the shear stress and can speed the avalanche. Heated water can vaporize to create a steam that carries the material downhill like a hovercraft on air. Minerals can melt under high temperatures as well. Friction can also crush some rocks into a powder that will lubricate the falling mass.

CAN LANDSLIDES BE PREDICTED? Landslides are major hazards that can lead to loss of important infrastructure, property, and human lives. It is possible to map areas in order to predict whether or not a landslide of some type is possible. If an area is at risk, decisions can be made to protect people and to avoid human triggers to the landslide areas. Geologists look at the geology of the land, the type of rock and soil in the area, what is being done to the area with regard to construction or agriculture. They also look at the 202

water patterns in a given area already at risk. The GIS or geographic information system technology uses remote sensing and computer analysis to predict high-risk areas for landslides. Existing landslides are photographed after the fact and combined with before the fact pictures in order to glean information on how to better predict future slides. The geomorphology of the area is also analyzed. This combination is perhaps the best way to gather real data that can be useful in prediction analysis.

EARTH FLOWS Earth flows are unique by the fact that they are very heavy with water and mostly fine sediment. They are denser than you'd think – rivaling traditional rock landslides. Even so, they have such a high liquid content that they will flow in ways similar to pure water. Speeds can be as high as 10 meters per second and can involve very large volumes of earth and water. There is evidence of gigantic flows like this in prehistoric times. The sediment is about half of the volume; water is the other half. Large mountainous flows can happen after a rainy season following a forest fire. Steep slopes of greater than 25 degrees and a lot of soil or other fine sediment add up to a situation where things can get deadly. In Japan, these flows are so large they are called Yama tsunami, which means a mountain tsunami. Often the front of the flow or the head of the flow contains the largest boulders. This is the flow surge that may also contain logs or other vegetation. Behind the head is smaller pieces of silt, sand, clay-like debris. The smaller particles have more fluid pressure in them so they are heaver as a mass and enhance the flow of the entire debris along its path. The flow will happen in pulses or surges with a head, body, and tail for each surge. Lahars are special flows that are related to volcanic activity. An eruption itself can cause the lahar or loose material from the flank of a volcano to mix with water. This forms a slurry of black volcanic rock that can flow or creep down to lower elevations.

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AVALANCHES While anything can be an avalanche, most are associated with falling snow and are also called snow slides. Snow plus ice and debris can rapidly descend any slope under the right conditions. Factors contributing to an avalanche include a lot of new precipitation, weakening of the shear forces on a snowpack, earthquakes, or human activities. Almost all avalanches are a combination of air and snow. Of course, debris can be picked up along the way. There are two major types of avalanches but many are mixed in their characteristics. You can have slab avalanches, which are blocks of packed snow that travel across a weaker layer or collapse a weaker layer. Next you have loose or fluffy snow packs. These will gain momentum and accelerate over time as the total mass increases. Air plus snow equals powder, which can also rapidly rush down the mountainside. You need snowpack that is relatively long-lasting plus a change in conditions. Winter and spring are prime times for this. It is possible to have summer avalanches as well. Many happen when there are storms that add to the snowpack or erode the top of the snowpack. Heavy melting from the sun are also secondary cause of avalanches. Earthquakes, rain, rocks and ice falling are both lesser causes of avalanches. Triggers might include skiers, explosives used for a controlled avalanche, and snowmobiles in the area. Sound has no impact on avalanches, contrary to popular belief. An avalanche tends to start slow but then, like a snowball, it picks up more material. If there is a weak layer, it will fracture and fall as a block. Thousands of cubic meters of frozen snow can be part of this process by the time it is over with. There is shear strength involved that is overcome by the weight of the affected snow. The end result is dependent on the humidity, temperature, and characteristics of the falling snow. The amount of solar radiation also matters because it will change the hardness of the upper layers of the snowpack. We do not know as much about avalanches as we do about landslides. Computer models and the study of existing and past avalanches will help geologists learn to better predict these and avoid them through the judicious use of explosives to clear the avalanche when it is safest to do this. 204

There are three types of known avalanches: 13. Slab avalanches happen when snow has blown in by wind in a block or slab that fractures off from the rest of the pack. There is a crown fracture like in a landslide, followed by flank fractures, and finally a sauchwall, which is what we call the fracture at the bottom of the slab. Now you can see that the slab can travel downhill with a wide range of depths up to 3 meters thick. About 90 percent of fatalities in hikers and skiers come from these types of avalanches. 14. Powder snow avalanche – these are very large and spectacular avalanches that are mainly a cloud of snow powder. It is sometimes known as a mixed avalanche because there is a denser layer beneath it. The trigger is usually a large recent snowfall of dry powdered snow. These are extremely fast at 300 kilometers per hour, very large, and travel a larger distance than you'd expect – even traveling uphill for a period of time. 15. Wet snow-type avalanches – these are much slower than powdered snow and have more water in them. There is more friction here between the falling snow and the inclined plane. While slower than others, they still reach speed of up to 40 kilometers per hour. Because these are so heavy, they are very destructive to property, vegetation, and the land itself. They start for various reasons but the main causative factor is the very wet snow that is nearly at melting temperature. These are sometimes called isothermal snow avalanches because they have temperatures near melting but remain frozen except where friction has taken hold. Climate change and springtime warming are the main cause of this. Avalanches must have some weak layer that is unstable beneath a slab of snow that is more cohesive. This is usually not visible when looking at the avalanche area. There should also be enough slope to overcome the tension holding the snowpack onto the slope. Again, avalanches are much harder to predict than landslides. Also, remember that they only occur on stable snowpacks that persist from year to year in some form. This means you are talking about high elevations and higher latitudes.

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KEY POINTS IN THIS CHAPTER •

Landslides are of different types and include different geological phenomena.

•

You can have slides, topples, flows. Falls, creeps, and lateral spread that are sometimes all called landslides, even though they aren’t.

•

Certain mass movements are rapid, such as landslides, while others are slow, such as creeps.

•

The physics of earth, debris, and water determine what type of land mass movement you see.

•

Avalanches involve snow and ice. There are several different types of avalanches.

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CHAPTER 13: QUESTIONS AND ANSWERS 1.

Which statement about landslides is not true? A. Most landslides have a trigger of some kind B. Landslides can occur underwater C. Human factors rarely contribute to landslides D. Landslides can involve anything from mud to large boulders and rock faces

What factor plays the largest role in a natural trigger for a landslide? A. Wind B. Water C. Vibrations D. Magma activity

When inspecting a landslide, you want to know the furthest point it traveled. What would you call this area? A. Toe B. Transverse crack C. Tips D. Scarp

You see areas near a landslide caused by tension on the upper elevation area probably just prior to the landslide. What would you call these areas? A. Radial cracks B. Crown cracks C. Transverse cracks D. Heads

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What type of mass movement is considered slow movement but picks up momentum gradually over time? A. Progressive creep B. Earth flow C. Lahar D. Debris flow

Which type of mass movement is most associated with fine sediment of varying types but without a great deal of moisture in it? A. Progressive creep B. Debris avalanche C. Seasonal creep D. Earthflow

What don't you see as friction plays a strong role in a rapidly moving rock or debris flow? A. The temperature of the material and ground heat up B. Minerals may recrystallize C. The shear stress increases D. Air can vaporize and create steam beneath the falling material

What statement is not true about landslide prediction? A. Landslides are unpredictable events that cannot be predicted. B. Geographic information systems or GIS is used for predicting landslides. C. Previous landslide information provides the best data for predicting future events. D. Prediction uses a variety of inputs, such as geology, land use, and geomorphology.

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In a slab-type avalanche, what is the sauchwall? A. The top fracture of the falling slab B. It is the bottom fracture of the falling slab C. It is the overhanging lip of the slab before it falls D. It is the fracture along the side of the slab

10.

In a wet snow avalanche, what is the main causative factor? A. Warmer temperatures B. Recent snowfall C. Seismic activity D. Windy weather

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CHAPTER 14: WATER AND GEOLOGY This chapter about water is important to the study of geology mainly because water shapes geologic structures to a huge degree. Water is contained in the hydrosphere but it interacts with the geosphere all over the world. You'll learn about streams, rivers, deltas, and basins and why you see them as critical parts of the geology of the earth.

WATER IN THE STUDY OF GEOLOGY Most of the earth is covered with water, which is the hydrosphere of the earth. Water is needed to deposit minerals from place to place, help rock materials become real rock in the process of lithification, and aid in rock weathering. It gets sucked into the earth's crust when subduction happens and gets spit back out as steam in volcanoes. Magma also emits water as it cools. The water cycle is more than ground to clouds and back again. Water goes through all three phases – solid, liquid, and gas as part of a cycle that includes evaporation, condensation, transpiration from leaves, precipitation as rain or snow, and runoff from the ground to watery areas. Figure 57 depicts this cycle well:

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Figure 57.

Notice that water gets into the atmosphere through evaporation aided by the heat of the sun and transpiration, which is what leaves and plants give off as part of photosynthesis. Sublimation can also happen when ice or snow give off water as a gas from its solid form, skipping the liquid layer in between. Evaporation comes from oceans, streams, river, and groundwater.

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Water condenses on the ground as dew in the cooler mornings and in clouds. Once condensed water in clouds is heavy enough to fall, it will come back to earth as rain, snow, sleet, or ice. This is precipitation. It becomes groundwater or lake and ocean water. Infiltration involves the soil providing water to deeper groundwater. This sifts through the rock and may come out in streams or lakes to reach the surface again.

WATER BASINS

Figure 58.

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Geologists divide landscapes into their different drainage basins. Other names for a basin are watershed or catchment. All precipitation in a catchment drains into the same stream. There are drainage divides that separate one basin or catchment from another. As streams travel further, they come together to make rivers that drain as tributaries into other rivers. Finally, all rivers or continental waters from them will end up in a larger area, such as an ocean. Figure 58 depicts a basin and its main features: Streams start as headwaters. These are often small tributaries or branches of larger streams or rivers to make a trunk stream. The mouth of the stream is where it ends and discharges its contents into something else. Two equal streams meet at a confluence. Many streams and rivers have a mouth in the ocean, which is where fresh water meets ocean water. Some do not ever reach the ocean. What then? These are closed basins or endorheic basins that end in a lake that just evaporates over time. The Great Salt Lake in Utah is an endorheic basin lake. You can describe basins in several ways. A basin is also what we call the entirety of land that drains into the endpoint, which is usually the ocean. Most of the Midwest and some of the eastern parts of the US are of the same basin. The west and part of the east are in their own basins. The Great Salt Lake area and several others in Eurasia and parts of Africa have their own endorheic basins.

SURFACE WATER EXPLAINED Streams are flowing bodies of water. In geology, the terms brook, creek, and river are not used. Everything is a stream. Streams cause a great deal of erosion all the time and send sediment downstream toward the oceans. There are two factors that affect the degree of erosion. The first is the velocity of the stream's water. How fast is it going? Second, you want to know the channel gradient, which is how downsloping the water is. It is measured in terms like feet per mile or meters per kilometer. A taller mountain with a stream probably has a larger channel gradient. Erosion of a stream leads to a valley over time. The wider the valley, the larger was a given stream at one point – even if it is narrow in the present time. The velocity or water speed you see in a stream depends on several factors. The channel gradient, the

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stream width, and the underwater terrain all determine the water speed. What's happening downstream also matters. If there are tributaries that are discharging water downstream, this will decrease the water speed to some degree. In most cases, the channel velocity increases as a stream gets wider, deeper, and has more tributary-fed water in it. The discharge of a stream is the stream size rather than its width or length. This is the volume of water flowing past any given point in the stream. It is measured in cubic feet, or cubic meters. In other words, it is a volume unit per time. A smaller stream will naturally have less discharge in it. Obviously, the stream's discharge will increase as you go downstream. So, if the stream gets shallower but stays the same width, the flow or velocity rate will increase as the same volume of water has a narrower area to squeeze through. Try this by putting your thumb on the end of a garden hose to see how this works. If you add more volume through a heavy rain or snowmelt, you will also get a bigger discharge and more velocity. Streams tend to be curvy so that they are a lot like half tubes. The water velocity will not be the same throughout. At a bend in the curve, you will see higher velocities at the outer edge of the curve. As the stream narrows, the highest velocity will be at the top and middle section – far away from friction near the bottom or edges. Geologists refer to a line called the thalweg of a stream, which is a stream's natural progression and its deepest channel. If you draw a line down the stream at its deepest depths, you will get the thalweg. Wherever there is water away from the bend and away from friction, you'll get faster speeds. The thalweg does not have to be underwater at a given point if it's part of the same valley. The pattern of all the tributaries in any region or area is the drainage pattern. There are many things that determine what this looks like, including the type of bedrock and whether there are local faults or folds to consider. As you study a geological area, keep these different patterns in mind as they will help you understand what the earth looks like beneath the watery areas:

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•

A dendritic pattern happens in spots where the bedrock is uniform, lies flat, and erodes in a uniform pattern. This is common and tree-like in appearance.

•

A trellis pattern happens when there has been a lot of earth-folding and differential erosion in rocks that are not flat. There might be ridges of resistant rock that prevent flow in one or more areas. This is seen in the eastern section of the US in the area of the Appalachians.

•

A rectangular pattern where the pattern of joints and faults determine where the streams are located and drain. It looks like a tree with square branches.

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Radial patterns are seen where streams flow down from a mountaintop or top of a cone-shaped volcano. Each stream might have a dendritic pattern of its own.

•

Deranged patterns have no real pattern and can involve streams disappearing into subterranean areas or underground streams.

FLUVIAL PROCESSES Streams also behave differently based on their fluvial processes. These are a combination of factors called fluvial processes. Fluvial processes are those things that affect the way a stream flows and why it is the way it is. These include the following: •

Erosion – erosion itself is due to materials carried down and abrading the river bottom, rocks that become round to nothing, the hydraulic action of the water against rock, and chemical corrosion from acidic water.

•

Transportation – eroded material must go somewhere. It tends to go downstream. Some rocks are large and roll slowly along the bottom, while others bounce along the bed of the stream. This is called saltation. Small particles are suspended in the liquid and anything dissolvable in water may stay in solution.

•

Deposition – this happens after the river has lost its energy and cannot transport anymore. Things just get deposited then, in places like estuaries or deltas. Where water velocity is slower, you might also get deposition upstream somewhere. Rivers will meander more if they are slower-moving.

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The alluvium is the sand and silt deposits around the floodplain areas. Because this sediment is very full of minerals, these deposits lead to fertile agricultural territory. In general, there are three major zones of a stream's system. The first zone in the headwaters area of a stream is the zone of sediment production. The second is the zone of transport throughout the length of the stream's course. Finally, you have the zone of deposition, where the mouth of a stream opens out into quieter water.

SEDIMENT IN STREAMS The sediment in a stream is called its load. It is divided into the dissolved, suspended, and bedload areas. The bedload is heavy and made of pebbles or boulders. Traction and saltation efforts bring them downstream. Suspended particles are visible but are light enough to be suspended in water. Then you have your dissolved load, usually mineral ions like potassium, sodium, chloride, calcium, and bicarbonate. They are unaffected by the flow of water. Streams move the fastest at the Bankfull stage, which is just prior to flooding. When streams overflow, the floodplain around it will have sediment that gets deposited along the banks when the flow rate drops dramatically after flooding. A natural levee is created along the edges in a ridge when flooding is repeated. Streams all have longitudinal profiles. They have all three zones in them, from the headwaters to the mouth. You will see this profile mapped out in terms of its elevation along its course and the gradients at each level. The profile is then a map of elevation versus length. You can see the energy in the stream drop from top to bottom but not in a linear pattern. The equilibrium of a stream is its grade, where the stream tries to balance the effects of erosion, discharge, gradient, velocity, and other things. The base level of a stream is whatever elevation it can erode to at its lowest point of its mouth. The base level is usually the ocean at sea level but a lake can be the base level of a stream entering it. If the sea level changes for any reason, the base level for many streams will also change. If you add a dam to the stream, you will get a rise in its base level. If you drop the base level, the stream will get deeper. This is because all streams

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want to erode down to the base level. A stream at equilibrium is known as a graded stream.

CHANNEL TYPES IN STREAMS Streams can have a wide range of patterns or channel patterns. Some wander in a meandering way, while others are straighter. These are the main channel types you will see in any stream: •

Braided streams – these are streams that break down and come together in complex ways, especially when the gradients are low and the sediment is coarse. Certain mountain or glacier streams can be like this.

•

Straight channels – these have V-shaped valleys that are narrow and steeper gradients. They tend to be more rapidly flowing than other streams.

•

Meandering streams – these are slower and curve back and forth. Remember that the water is fastest on the outer edge of the curve so you'll get a cut bank, which is an area of erosion where the meandering stream is trying to extend itself. The point bar is on the inner aspect of the loop, where there is added sedimentation. Some rivers meander in deeply entrenched valleys or canyons. They started out on plateaus and cut through bedrock over millions of years. Meandering can get so extreme that it cuts off a segment of it to create a lake near the re-cut stream, called an oxbow lake. An oxbow lake is a former meandering channel. It can fill in with sediment over a period of time to make a meander scar.

Alluvial fans are landforms made from stream deposits. They fan out from the mouth of the stream into valleys from mountain canyons where the sediment just kept going until it met the slow moving valley floor. You often see these in drier regions of the world.

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DELTAS A delta is formed when deposits settle out in a broad area around the mouth of a big river. The Nile delta and the Mississippi River delta are two of these. You can't make a delta if erosion or wave action is too severe. You also need a lot of sediment to create a delta. The Mississippi River delta is not the same as it was because human engineering has reduced the sediment output from the river. The output of sediment drifts out of just one of its mouth sections. Rising sea levels have also affected what the delta looks like in the Gulf of Mexico. Finally, engineering has straightened the river so it is shorter. This also reduces sediment. Deltas can be shaped by waves or the tides. A tide-based delta will not be as fan-shaped because the tides will come in and fall according to the geology of the area and not as much related to any wave action. Stream terraces are related to old floodplains and are located above existing floodplains. They can be seen when glaciers retreat and flood an area or when a stream erodes downward to create terraces along the stream.

WATER UNDER THE GROUND An aquifer is any rock that contains water you can extract. It needs to be porous and water-permeable in order to be a good aquifer. A porous area has space for water to drain through grains of sand, for example. Vesicles in volcano-based rock also add to porosity. Compaction and cementing of rock will both reduce the porosity of rocks. Permeability is just the ability to move water through something. Shale is porous but the pores don't connect well to one another, so it isn't permeable rock. A good aquifer must also contain drinkable water or it doesn't help humans much with well-digging. They can be large or small and will be good for water supply if they have the 3 Ps of potabilty, porosity, and permeability. Water seeps into the ground and enters what's called the vadose zone. It is also called the zone of aeration. Plant roots exist in this area. Below this zone is called the capillary fringe, which is thin. The pores in the rock are filled with water and saturated. Capillary 218

action sucks water into the pores there. Beneath that is the zone of saturation, where the fluid pressure in the pores is high. The capillary fringe is where the water table is located. Figure 59 shows these layers:

Figure 59.

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At the water table, you will have pores of rock that are saturated completely with water. The best case scenario is when there is no confining layer of rock above it that will pressurize the water enough to push it up too high after the water table has been reached. The confining layer is called the aquitard layer; it isn't very permeable so water doesn't get through easily. Aquiclude layers have no permeability to water at all. There is water beneath that under pressure. If you reach that layer, you will get artesian water or confining water. Beneath that is more rock and finally what's called the bedrock aquifer. Springs that pop up through faults under pressure are called artesian wells because this is the layer that water comes from. Artesian wells are areas of discharge of the groundwater to the earth's surface. Streams that pop up out of nowhere are also discharge areas. Playas in deserts are the same type of place. In a perfect system, we humans would extract water from wells in the underground aquifers in the exact amount it is being replaced through precipitation. Unfortunately, this is not happening in many parts of the world. Too much water is being pumped out of aquifers and the ground water drops. The earth itself can drop as a result; this leads to things like subsidence or sinking of ridges and sections of earth you might see in the American Southwest. These areas need the pore pressure of water in the rock's pores to hold up the earth. Without this pressure, the earth just sinks.

HYDROLOGY-BASED EARTH FEATURES When limestone and other salts dissolve in and around the earth, you get what is called karst. Karst can mean a lot of things. You can have karst towers above the ground where rock is left over as a tower after some of it has dissolved away. Caverns, disappearing streams, and sinkholes are all types of karst. Acid rain will accelerate the formation of karst because it makes carbonic acid. Carbonic acid is rough on the calcite in limestone and will dissolve other salts as well. What happens to dissolved calcite, which is in solution underground? It will often redeposit elsewhere. When it does, it is called tufa or travertine. Speleothems are travertine deposits in caves. You know them as stalactites and stalagmites. 220

COASTLINES Coastlines are the interface between water and land. Waves in water will affect the land in many ways, especially along coastlines. Let's look briefly at why we get waves. Waves on the surface of the water are from wind energy transferred to water due to the friction between the water and blowing air. Water moves in waves that have crests or peaks and troughs or lows. The distance between a crest or trough is called the wavelength, while the height of the wave or wave height is from the crest down to the trough. The wave amplitude is not the same as the wave height. It is defined as half the wave height and is measured from the middle point to the crest. The wave period is the time it takes to get one crest to pass and another to arrive at any given point. The wave speed or velocity is the forward momentum or energy of the wave in distance divided by time. The wave base is the spot below which the water is undisturbed by wave activity. The fetch is the distance involved in the blowing of any wind. A long fetch means the wind energy was strong. Figure 60 shows wave anatomy in detail:

Figure 60.

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The inside of a wave will be a circular orbit of water. This works great until the orbit gets too elliptical. Then it just breaks and crests as a breaking wave. Waves near shore will break because the ground beneath the ellipse of water interrupts the ellipse action. The wave then just breaks at that point and rolls to shore. Waves in the ocean away from shore are choppy. This is because waves are coming from all over and are cancelling themselves out. Near the shore, you get breaking waves that are mostly of the same height and frequency. Tsunamis are not caused by wind but are from energy you get off the sea floor after an earthquake, eruption, or landslide. Water lifts and bulges upward to create a high energy wave that can travel far without loss of much energy. The wavelength of these waves is so long, you wouldn't necessarily notice them in deeper waters. The wave heights of these waves are low so it takes shallow waters to see them and feel their tremendous energy. Coastlines around earth are complicated. Not all are sandy beaches with gentle wave action. Coastlines include all inland and ocean to land interfaces. All interfaces like this are called littoral zones. These are divided into several parts, including these: •

Offshore zone – this is the part always below water. The area is affected by turbidity and currents.

•

Nearshore zone – this area is where the water depth is less than half of a wavelength of an onshore wave. The width of this depends on how shallow the area is.

•

Shoreface zone – this is where sand is deposited and continually disturbed. There are two parts of this; the upper and lower parts. Only the upper part is disturbed all the time. The lower part only gets disturbed when there are storm waves.

•

Surf zone – this is where waves break and surfers surf.

•

Foreshore – this is the wet or dry sandy areas where sand might be sorted on a beach. Waves wash up this part and backwash rolls back into the ocean.

•

The berm is the ridge you'll see where people put their dry beach towels. There are often two berms. The summer berm is closer to the water because wave action 222

is not as steep. Winter berm is a sand ridge built up when winter wave energy is greater and waves pile up sand further inland. •

The backshore – this is the area above sea level all the time, but is where sand dunes can build up due to blowing sand.

Waves rarely hit the land at a perpendicular angle or dead-on. They refract off the coastline at some other angle, even though it doesn't appear that way. This is because waves bend near shore and come on looking straight. There is actually a longshore current that drags sand down the coast in what's called longshore drift. In North America, most longshore drift is from north to south. Wherever the water is quieter, sand will tend to be deposited. Rip currents happen when a wave train comes straight onto the shore at a 90 degree angle and has no place to go after that because of an inlet of some kind. The rip current is the effort by this energetic water to get back out to sea. It usually slips out through a narrow but intense current that can carry swimmers with the current straight out into the ocean. The only way back is to swim parallel to the beach, get out of the current, and ride the waves back to shore. Undertow is different from a rip current in that it is under the wave. It is strong near the surf zone area and represents the water slipping back to the ocean to make up for the wave above it pushing water toward the shoreline. Cliffs, exposed areas of bedrock, rocky shoreline, stacks, arches, and other features represent emergent coasts where the sea level has fallen somewhat relative to the land. A submergent coast is the opposite – where the sea level rises and buries some of the land near the coast. Sometimes, tectonic activity leads to a sudden submergent coast as the earth sinks. This is how you get lagoons, estuaries, tidal flats, fjords, and barrier islands. A fjord is a glacial valley that has become flooded by sea level after an ice age. Tidal flats are mudflats that change with the tides. The three major sections of tidal flats are the barren zones, the salt pans, and the marshes. Barren zones are linked to stronger water that has coarse sediment. You might see ripple marks in this region. Marshes are wetter and vegetated with both sand and mud. Salt pans or salt flats are not submerged as much as the other areas, so they are full of fine-grained silt and/or mud. 223

Lagoons happen when spits or even barrier islands are in the way of open ocean. Estuaries happen when a lagoon becomes so far inland that the water becomes brackish, which is in between ocean salinity and fresh water. These are more vegetative and have their own unique characteristics. Lagoons and estuaries are both interesting transitions between land and water that also have complex marine and vegetative properties because of the way water and land interact in them.

GEOTHERMAL FEATURES The earth is hot inside so you can get many geothermal features based on the rising of this heat from inside the earth and water in nearby areas. Magma will easily heat the groundwater, creating steam as a result, and much hotter water than you'd expect from surface water. As water heats, it is less dense and rises to the surface through cracks in the ground. At the surface, you get some amazing things. Some geothermal energy is harnessed to create heat for places on earth that need a cheap source of this type of energy to heat their homes. An added benefit is the geothermal minerals that you can get from the deeply-generated water, including gold, mercury, and many others. Hot springs are simply heated springs in volcanic areas. Some areas are much too hot if it is near an active volcano. Other non-volcanic areas are less hot but still warm enough to bathe in. These are where the water has a chance to come up from the deeper areas beneath the earth. Geysers are famous geothermal structures. They are areas open to the surface but represent complex plumbing down below. Ground water areas accumulate and heat up to the point of flash steaming. This flashpoint leads to a sudden expansion of the water vapor that forces water out of the opening. In more stable areas, this repeat of heat and water expulsion leads to eruption of a geyser in a rhythmic fashion. Old Faithful is a geyser in Yellowstone Park that goes off every 65 minutes. Fumaroles are areas where magma has a channel through the water table area. The magma is very hot and can be liquid or just recently solidified. Water in the ground will heat up and be released as steam. You might also get hydrogen sulfide gas from the magma as well, so you'll smell the familiar rotten egg smell from these steaming vents.

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Depending on the gases emitted, some of these fumaroles can be dangerous to humans nearby. Rocks near fumaroles will look different or will have different chemistry because of the chemical reactions between gases and rocks in the vicinity of these vents. Mudpots involve less geothermal energy. Small amounts of water are involved, along with a fair amount of fine clay and mud. There will be local bacteria and acid in these waters that form thick pools of bubbly mud, often without a lot of evidence that they are there as they pop up randomly in non-volcanic areas.

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KEY POINTS IN THIS CHAPTER •

Drainage basins are the land areas all draining into the same place. Most drainage basins drain into the ocean.

•

Streams are what geologists call all flowing bodies of water. The size of a stream is dependent on the volume of water flowing past a single point in a set period of time.

•

A thalweg is a line drawn by measuring the deepest point of any stream and connecting the dot along the stream at those point.

•

Erosion of a stream depends on several factors. Most of it has to do with the energy of the stream's waters and the way the stream is flowing. Slower streams meander, while faster ones do not.

•

Aquifers are areas where the groundwater is accessible and drinkable after it has filtered through pores in the rock.

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Shorelines are made by wave action. Waves have certain features and are generated by wind activity.

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Waves do not hit most land at a 90-degree angle but tend to push sand down the coastline in a longshore current.

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Geothermal activity leads to several phenomena related to water, such as fumaroles, geysers, mudpots, and hot springs.

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CHAPTER 14: QUESTIONS AND ANSWERS 1.

When plants undergo photosynthesis they give off water into the atmosphere. What is this called? A. Transpiration B. Evaporation C. Sublimation D. Condensation

Snow will give off gas from solid to vapor phases, bypassing the liquid phase. What is this called? A. Transpiration B. Evaporation C. Sublimation D. Condensation

You measure the water velocity of a stream that started in a mountain and ended with several intervening tributaries. Where would you expect the channel velocity to be the greatest? A. At the mouth of the channel near the ocean B. At the base of the mountain C. Near the top of the mountain D. Where a tributary means a larger one

You are documenting a stream size. How do you describe the stream's size correctly? A. It is the width of it at its mouth B. It is the stream's volume output per unit of time at any spot C. It is the total water volume of the stream D. It is the total length of the stream

What drainage patterns of streams is the most common one? A. Dendritic 227

B. Rectangular C. Radial D. Trellis 6.

The fluvial processes dictate a stream's character. What is not a fluvial process related to erosion? A. Abrasion B. Saltation C. Corrosion D. Hydraulic action

When you dig a well, what layer beneath the earth do you want to reach and get below? A. Zone of aeration B. Capillary fringe C. Vadose zone D. Aquitard layer

What rock layer beneath the ground is impermeable to water? A. Aquitard layer B. Capillary fringe layer C. Aquiclude layer D. Vadose zone

Where on a shoreline would you put your beach towel to be as close to the water as possible without much of a chance of getting wet? A. Foreshore B. Backshore C. Berm D. Shoreface zone

10.

Water coming onto shore in some cases has a narrow pathway out, such as in an inlet area. It forms a path to get out that has a lot of energy and can drive swimmers to sea. What is this called? 228

A. Rip current B. Longshore current C. Undertow D. Rogue wave

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CHAPTER 15: GLACIERS AND GLACIATION This chapter covers glaciers and how they shape the geomorphology of the earth. Glaciers represent the cryosphere of the earth. While there are more or fewer of them at any given point in time, glaciers still exist today in pockets all over the earth. You'll learn how important glaciers have been in shaping the land and water features in all the continents of this planet.

GLACIERS AND THEIR FORMATION The earth has a cryosphere made of ice. Glaciers are a big part of this ice resource. Icebergs are another part of the cryosphere. Glaciers are so big that they retain some of their ice year-round on land. As of now, they cover just about 10 percent of the surface of our earth. They are so heavy and sometimes massive in their surface area that they have great powers of erosion. You need a combination of cold and wetness to have a glacier form. High elevations help to have this combination in parts of the world at lower latitudes. Glaciers happen when there is an accumulation of snowfall each year so that the snow becomes deep – so deep that it never completely melts. The layers just pack on each year in what's called perennial snow. This leads to a snow field that compacts over the years to bond to all the adjacent layers. The older layers become firns, which are masses of granulated ice crystals. As the firn layer gets compressed and further buried, it just recrystallizes into a solid, minimally porous batch of ice. Even though it is solid, this glacial ice is unique and has air pockets that trap that year's atmosphere in it. Glaciers are either alpine glaciers or ice sheets. Alpine glaciers are also called valley glaciers. They are found everywhere there is a big mountain range – the Himalayas, Alps, Andes, and Rocky Mountains. Long and narrow valleys are most prone to having these glaciers. Ice sheet glaciers once covered the major continents; these are very large and miles thick in places. The ice sheets you see now are in Greenland and Antarctica

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almost exclusively. Greenland's ice sheet is nearly one mile thick. Antarctica is home to a much bigger ice sheet that is 2.5 miles thick at its thickest. It is so large it presses on the bedrock beneath it.

HOW GLACIERS MOVE Ice builds up on glaciers and the glacier starts to flow based mainly on the fact that it is heavy. Ice can flow from deep beneath the glacier, even though it seems rigid. The fastest movement happens in the middle with melting at the bottom if the temperature gets too high. Ice melts under its own pressure so the glacier will flow along its own meltwater slide besides having its own internal flow pattern. At the top of a glacier, you have large crevasses, which happen because the top 50 meters of a glacier is too brittle for the kind of flow you see inside a glacier. These are hazardous to hikers because they can be easily hidden by snow. Below this brittle zone, you will see a more malleable layer called the plastic zone. Most of the glacier is in this zone. Expect to see a lot of sediment throughout the glacier. It is this sediment that most contributes to erosion beneath the glacier.

GLACIAL BUDGET The glacial budget is the balance of ice on a glacier. More snow compared to melting leads to a higher amount in your glacial budget. A negative balance means that more melting has occurred than you have added that year. The zone of accumulation of any glacier is where ice adds on, while the zone of ablation is where the ice is shrinking. There is a line of equilibrium between these two zones. The zone of accumulation is near the summit of a glacier and the zone of ablation is near the lower elevations. This means that the line of equilibrium is a vertical line somewhere on the glacier. The glacial budget depends most on how much melting you get each summer. Global warming is affecting the major ice sheets. They thin out dramatically in summer but more so now with the climate change. Calving happens when ice sheets break off to become icebergs.

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LANDFORMS CAUSED BY GLACIERS There are two major geology features that are seen geologically because of glaciers. These cluster into depositional phenomena and erosional phenomena. They are named differently based on where you live on earth. The landforms you see from erosion happen when glaciers slide over hard bedrock. Glaciers tend to pick up stuff along the way and drop them in various places that they travel to. Fine sediment is called rock flour. This is like the fine grit you'd use in a rock tumbler. This is how you get glacial polished rocks. Glacial striations are grooves made by larger pieces that scrape over rocky surfaces. Alpine glaciers can carve out their own valleys. They will not be V-shaped like streamcarved valleys but will be U-shaped instead. If you see two side-by-side valleys made from glaciers, you can see a ridge between them called an arete. The bowl at the top of the valley is known as a cirque, where the glacier carved out a section of the mountain. Figure 61 shows a cirque carved out by a glacier:

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Figure 61.

Cirques will fill with precipitation and form a lake millions of years later. This lake was known as a tarn. When a small glacier feeds into a larger one, the small glacier doesn't cut down as much. Millions of years afterward, you can get a hanging valley, which is a valley that has a drop off at the end of it, where the larger glacier was. This hanging valley might have a nice waterfall at the end of it that flows into the larger main valley. Depositional land forms involve stuff left over after a glacier has retreated. There are a lot of these in areas where glaciers once were. All glacial sediment is called till after it has been dropped. It is not well sorted as it drops. Tillite is any rock that started out in a glacier at some point. Diamictite is rock made from glacial till that has become lithified into a bigger rock. A moraine is a big ridge of deposits left by a mass wasting event after a glacier carved out a valley. Glaciers are a lot like conveyor belts. They pick stuff up at one end and dump it off at the other. Remember that glaciers have internal flow so moraines exist even if a glacier isn't advancing in any way. Terminal moraines are at the end of a 233

glacier, while recessional moraines are left by retreating ones. Lateral moraines are seen along the sides of a glacier as ice wastes from its edges. You can even get a medial moraine if two glaciers merge to form one. The medal moraine will run between the two halves. Ground moraine is just the random trail of stuff left behind as the glacier melts. Other terms used to describe the depositional landforms of glaciers are these: •

Outwash plains are mixtures of sand, silt, and gravel made by glacial grinding and carried along by water.

•

Glacial erratics are large boulders glaciers deposit far from their origin.

•

Kettles are depressions left behind when a large ice block melts and leaves till around it.

•

Kettle lakes are kettles that are formed by these kettles.

•

An esker is a long, snake-like deposit of sediment in a ridge that was once a stream under a glacier.

•

A kame is a mound of till from dripping meltwater off the edge of a glacier or through the glacier itself.

•

Drumlins are teardrop-shaped hills with a steep side pointing to the upstream area of an ice flow. The low side points in the direction of ice movement. They may be due to a combination of deposition and sculpting.

GLACIAL LAKES A lake within a cirque you already know is a tarn. There are many of these lakes in the Western part of the US after alpine glaciers retreated. Recessional lakes leave behind isolated basins along a glacial valley. These cause a chain of lakes known as paternoster lakes. Long carved lakes are called finger lakes. Large proglacial lakes exist when a continental glacier exists. These are found along the glacier edges. Lake Agassiz in Manitoba was a giant proglacial lake at one time but now has shrunk in size with Lake Winnipeg as its only major remnant. Lake Missoula is another proglacial lake from the Laurentide ice sheet.

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Pluvial lakes were proglacial lakes found in more humid environments when evaporation wasn't as prevalent. This was the case in the last ice age in the western US. Several lakes in Nevada, Utah, and nearby areas were pluvial lakes. Lake Bonneville was one of these. It breached at one point to create the Snake River in Idaho. This breach drastically lowered the lake levels over a short period of time. The five Great Lakes we see in North America are proglacial lakes from the last ice age. The remnants of Lake Bonneville is the Great Salt Lake.

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KEY POINTS IN THIS CHAPTER •

Glaciers can be large sheets on major continents or sit in valleys as alpine glaciers.

•

Glacial ice is layered and comes from packed snow that persists year after year.

•

Glaciers move internally as well as downhill on melted water slides beneath them.

•

Glaciers have depositional and erosional features.

•

Glacial erosion can create polished areas of rock and U-shaped valleys.

•

Deposition of glaciers leads to till. Till can be very fine or as large as erratics left behind as glaciers retreat.

•

Glacial lakes are often very large. The current five great lakes in the US Midwest are proglacial lakes from the last great ice age.

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CHAPTER 15: QUESTIONS AND ANSWERS 1.

What phrase best describes how glacial ice becomes the way it is? A. Freezing of rain in layers B. Re-freezing of melted snow C. Compaction of perennial snow D. Solar radiation effects on snowpack

Ice sheet glaciers can get thick. How thick is the current thickest ice sheet glacier on earth? A. 500 feet B. 2.5 miles C. 10 miles D. We don't have these on earth anymore

What is the major byproduct of calving of glaciers? A. An increase in icebergs B. An increase in glacial thickness C. An increase in the zone of ablation D. Increased glacial sheet size

When a glacier lobe erodes into a mountain to form a bowl-shaped depression that later fills with water, what is this lake area called? A. Col B. Arete C. Tarn D. Cirque

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Glacial moraines are named by where they are with respect to the glacier. Which type of moraine is made when two glaciers merge? A. Medial moraine B. Recessional moraine C. Lateral moraine D. Terminal moraine

When an ice block from a glacier gets left behind and melts to form its own collection of tills, what is this called? A. Kame B. Kettle C. Erratic D. Esker

What is a long sinewy band of sediment left behind when streams flowed beneath the glacier called? A. Kame B. Kettle C. Erratic D. Esker

What is a large boulder left behind after a glacier has retreated called? E. Kame F. Tillite G. Erratic H. Drumlin

What type of lake was Lake Agassiz in Manitoba? A. Finger lake B. Proglacial lake C. Paternoster lake D. Kettle lake

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10.

Which lake is the remnant of Lake Bonneville? A. Great Salt Lake B. Lake Superior C. Lake Ontario D. Lake Erie

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SUMMARY Hopefully, you now have a much greater appreciation for every rock you see. You likely understand the basic types of rocks and how they have developed through the ages. Geological time is very long, so most of the rock to see have a long history dating from billions of years ago. In this course, you studied rock formation through the diverse actions of the earth's crust, a long history of sedimentation processes, the flow of water and air, and the heat of fire – and many more processes that shape every rock, river, and valley you encounter in everyday life. You now know why the study of geology is important, even if this is not your college major. Chapter one introduced the basic terminology you needed to know to get started in the subject of geology. Geology is one of those courses where there is a lot of lingo to learn in order to even get started. This chapter simply got you started on your geology adventure. You also learned about the 3 basic types of rocks and how they come to be rocks in the first place. Chapter two began our discussion of planet earth and its many unique features by looking directly at its origins. You learned that the earth is about 4.54 billion years old and began as a giant cloud of swirling space dust. Boy, has it changed! We looked at how all that dust collected into the wide range of rocks, minerals, and amazing geological structures on land and sea we now research in geology. At the end of the chapter, you studied the continental features and seafloor landscape and why they exist as they do now. Chapter three allowed you to examine the concept of geologic time. As you know, this timeframe dates back to the first days when the earth's crust was being developed. Older rocks look different from younger rocks; you needed to know the difference between them. You learned how to date rocks and how you can use rocks to indicate the age of

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fossils. The chapter also looked at the different types of fascinating fossils you can find in your own back yard or nearby rock quarry. Chapter four involved a discussion of what we know about plate tectonics. You learned that it is still called "plate tectonic theory" even though there aren't any legitimate counter-theories on why the continents exist at all and where they are located. You also saw what plate tectonics means for geologists. Clearly, the earth is still changing and phenomena like earthquakes and mountain-building can be easily explained by understanding how the lithosphere moves on this planet. Chapter five in the course finally began to talk about what many people think geology is all about – cool rocks and minerals. You saw that a mineral is a hardened substance from the earth that is made from single element or just a few elements in a chemical compound. The two main mineral classifications you learned about are the silicates and non-silicates. You studied how to classify and identify the most common minerals you'll find around the world and even in your own backyard. Finally, we got into detail on the subject of igneous rocks and their formation in Chapter six of the course. You learned that igneous rocks are literally born out of fire – the first rocks to be spit out of our molten interior. After reading this chapter, you could see all of the stuff that's in magma and how it turns into the rocks you see all the time. Magma is more than just underground lava. You were able to study and learn about the amazing things that happen when it cools and the ways the minerals precipitate out of it when that occurs. Chapter seven delved into volcanism and the volcanoes we have on earth. Volcanoes help dispel the heat from inside our planet and contribute to new land formation in some parts of the world. You learned just how magma is extruded from deep within the earth through volcanic activity. You already knew that lava is just surface magma but soon learned that there are several types of volcanoes and volcanic eruptions all over the world. We also discussed how volcanic eruptions might be predicted. Chapter eight in the course covered weathering and its effects on geology. Weathering is inevitable and can change rock faces for many reasons. You learned how these work with regard to sedimentary rocks and how weathering creates soil. You saw how soil is

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different all over the world for many reasons. You also studied how soil forms and what makes each soil type unique. Weathering can create ore deposits, as you also learned. Chapter nine allowed you to finally learn about sedimentary rocks. You saw that if igneous rocks are basically the primary rocks, then sedimentary rocks are secondary. These are the rocks that start out as smaller pieces called sediments, becoming lithified to form their own kind of stone. You learned how to name sedimentary rocks and what we gain economically from products these types of rocks provide us on earth. Chapter ten in the course rounded out the discussion of rock types by revealing how we get metamorphic rock. Things, pressure and heat cause metamorphic change in rocks, leading to many different rock types. You now fully understand the complexities of metamorphism and how they lead to several types of new rock from old rock. Chapter eleven in the course is about earthquakes. Studying earthquakes reminds us that geology isn't just about rocks. You learned in this chapter that earthquakes are perhaps the best proof that plate tectonics is not theoretical. They happen mainly when two or more plates are moving in directions that are not congruent with one another. You also learned how earthquakes are measured and saw why they cause so much damage. Chapter twelve taught you how and why rocks deform. You saw that while rocks seem so solid, the awesome powers of earth movement can still create giant mountains and crush sedimentary rock into much harder metamorphic rock. You hopefully learned the patterns of rock deformation and understood the types of stress the earth's crust is under on a daily basis. The chapter helped you understand why the earth has the interesting topography it has now and why it will probably continue to have even more interesting and different topography in the future. Chapter thirteen in the course helped you understand better the geological phenomena seen due to the effects of gravity. You were reminded that gravity pulls everything toward the center of the earth so that heavy things that don't have the necessary friction or infrastructure to hold up properly will fall down. Rock, dirt, sediment, snow, and ice all participate in this process to create things like landslides,

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mudslides, flows, and even avalanches. You also saw that there are more forces at play in these gravity-based situations besides the law of gravity. Chapter fourteen was a study of water; you learned that it is important to study water in geology because water shapes geologic structures to a huge degree. Water is contained in the hydrosphere but it interacts with the geosphere all over the world. You learned about streams, rivers, deltas, and basins and why they are such critical parts of the geology of the earth. Chapter fifteen in the course covered glaciers and how they shaped the geomorphology of the earth. You now know that glaciers represent the cryosphere of the earth and that, while there are more or fewer of them at any given point in time, glaciers still exist today in pockets all over the earth. You also saw just how important glaciers have been in shaping the land and water features in all of the continents of this planet in so many ways. After studying geology as a science with a lot of different features to consider in this course, rocks now likely take on a new meaning to you. While you may not be able to name every rock you pick up off the ground, you probably can understand in a new light how it came to look the way it does. Who knows? You may have decided to make geology a topic you want to study further. Good luck!

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COURSE QUESTIONS 1.

You find a rock that is fine-grained. What size granules must it have? A. Less than 0.1 mm in diameter B. Less than 1 mm in diameter C. Less than 5 mm diameter D. Less than 8 mm diameter

The flat area along the sides of a river bed as it travels is called what? A. Delta B. Tidal zone C. Brackish waters D. Floodplain

What is not something generally associated with metamorphic rocks? A. Chemical changes B. Magnetic changes C. Mechanical changes D. Biological changes

The part of the earth associated most with geology is called what? A. Stratosphere B. Inner core C. Lithosphere D. Troposphere

The substance that most invertebrate shells are made of is what? A. Iron sulfide B. Calcium carbonate C. Silica D. Sodium chloride 244

A substance that crystallizes in rock to form a regular structure as it solidifies is called what? A. Basalt B. Magma C. Mineral D. Mica

What type of rock is a common sedimentary rock? A. Sandstone B. Granite C. Basalt D. Diorite

What is the primary process you see that leads to rust out of iron deposits in rock? A. Weathering B. Plucking C. Saltation D. Oxidation

What is lahar usually made of? A. Mud B. Sand C. Pumice stone D. Magma

10.

The shiny flaky stuff you find in schist is called what? A. Calcium carbonate B. Ooliths C. Foliation D. Mica

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11.

The type of igneous rock that has the largest inclusions is called what? A. Diorite B. Gabbro C. Basalt D. Diabase

12.

What will you see with regard to magma cooling and the size of its inclusions? A. Slow cooling equals small inclusions B. Fast cooling equals large inclusions C. Slow cooling equals large inclusions D. Fast cooling and slow cooling have the same inclusion size

13.

How does most sediment come to form sedimentary rock? A. Through precipitation B. Through recrystallization C. Through gravity D. Through mineralization

14.

What is a rock called that has been deposited a long way from its origins due to the actions of a retreating glacier? A. Intrusion B. Erratic C. Extrusive rock D. Interlocking rock

15.

What type of lava specifically comes up from the seafloor? A. Pele's hair B. Pyroclastic flow C. Pahoehoe D. Pillow lava

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16.

The area in a desert that occasionally fills to make a temporary lake is called what? A. Playa B. Sea-rack C. Moraine D. Lahar

17.

What factor most contributed to the development of earth's outer crust? A. Gravity B. Water C. Oxygen D. Sun's energy

18.

What was the least common gaseous substance in the Hadean Era of earth? A. Oxygen B. Carbon dioxide C. Water vapor D. Sulfur compounds

19.

What gaseous substance most helped contribute to limestone formation? A. Oxygen B. Nitrogen gas C. Carbon dioxide D. Sulfur dioxide

20.

What did the first land surfaces on earth probably look like? A. Flat sandy beaches B. Rocky mountains C. Jungles D. Black volcanic islands

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21.

Which supercontinent occurred last in geological time? A. Pangaea B. Rodinia C. Kenorland D. Vaalbara

22.

What part of the earth's spheres is where we have the rocks beneath the earth's surface? A. Biosphere B. Hydrosphere C. Cryosphere D. Lithosphere

23.

What layer is attributed to a chemical layer of the earth and not to a rheologic layer? A. Lithosphere B. Asthenosphere C. Mantle D. Mesosphere

24.

Where would you imagine the earth's crust to be the thinnest? A. Mid-Pacific B. Antarctica C. Western USA D. Middle of Africa

25.

What layer beneath earth makes up most of its volume? A. Outer core B. Mantle C. Inner core D. Crust

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26.

What substance makes up most of the earth's outer core? A. Iron B. Palladium C. Silicon D. Nickel

27.

What part of the earth's layers is most responsible for the earth's magnetic field? A. Crust B. Mantle C. Outer core D. Inner core

28.

What metal might you least find in the inner core of the earth? A. Gold B. Sodium C. Silver D. Palladium

29.

What activity likely created a seamount in the ocean? A. Tectonic plate separation B. Tectonic plates coming together C. Volcanoes erupting D. Sediment falling

30.

Where does the biogenous contribution to the ocean floor sediment come from? A. Glaciers B. Seashells C. Comets D. Rainfall

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31.

In what area of the North American continent will you find Precambrian rock more easily? A. Florida coast B. Hawaii C. Southwest deserts of US D. Ontario

32.

What best describes the Proterozoic era regarding the earth's crust and its plates? A. The plates were thinner and moved more quickly than now. B. The earth was mostly without any solid features. C. The continents were much like they are now. D. There were a few cratons but not any solid continent or supercontinent.

33.

The eukaryotes were not the first organisms on earth. What was not generally a feature of these organisms? A. They were capable of being multicellular. B. They had clusters of chromosomes. C. They can reproduce sexually. D. They were all photosynthetic.

34.

What is not considered a probable cause of the snowball earth that happened about 700 million years ago? A. The sun was not as strong as it is now. B. The earth was more tilted than it is now. C. The ice on earth was too reflective of the sun's rays. D. There was more oxygen around the earth and oxygen is not a greenhouse gas.

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35.

You find some rocks with fossils of the Paleozoic era. Which fossil type might you see from the Paleozoic era you would consider the earliest among them? A. Crinoids B. Trilobites C. Mollusks D. Brachiopods

36.

What was a key feature of many of the known arthropods emerging in the Paleozoic era? A. They were able to swim in water. B. They were very large. C. They were photosynthetic organisms. D. They had a calcium carbonate shell.

37.

Which period is not from the Mesozoic era? A. Triassic B. Jurassic C. Silurian D. Cretaceous

38.

What animals were dominant on land during the Mesozoic era? A. Dinosaurs B. Amphibians C. Insects D. Mammals

39.

What was the cause of the mass extinction leading to the end of the age of the dinosaurs? A. Volcanic activity B. Plant overgrowth C. Rise in seawater D. Asteroid impact

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40.

In dating rocks, what would least likely help you? A. Carbon dating B. Magnetism C. The principle of horizontality D. Fossils

41.

Which is not a known principle of stratigraphy? A. Horizontality B. Laterality C. Superimposition D. Cross-cutting relationships

42.

You see a cross-cutting layer in sedimentary rock. What would you see as a main feature of this? A. It is thinner than the other layers B. It is more mineralized than the other layers C. It is shinier than the other layers D. It is diagonal with respect to the other layers

43.

What is not a key feature of an index fossil? A. It lived a long time span. B. It is easily identified. C. It is from a common species. D. It is widespread across the world.

44.

Which dating technique for rocks would not work for those dating from billions of years ago? A. Radiocarbon dating B. Potassium-argon dating C. Uranium series dating D. Fission track dating

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45.

Which absolute dating method is not based on imperfections or traps in crystals that trap escaping electrons from other atoms? A. Thermoluminescence B. Potassium-argon dating C. Optical stimulating luminescence D. Electron spin dating

46.

What ore is most used in dating rocks for its radioactivity? A. Thorium B. Gold C. Tungsten D. Uranium

47.

You might see a body fossil in amber. What is amber? A. Solidified lava B. A golden mineral C. Hardened tree sap D. Crystallized golden quartz

48.

What did researchers notice most about the earth's crust when using bathymetry? A. That the crust was made of basalt in the ocean B. That there were mid-oceanic ridges in all major oceans C. That earthquakes occurred in the oceans D. That the earth's crust was very thin in the oceanic areas

49.

What did magnetic striping seen on the ocean floor indicate about the movement of the continents? A. That the continents were traveling in a northward direction. B. That the ocean is spreading out slower than before. C. That mid-oceanic ridges have shifted over time. D. That the earth has changed polarity as the oceanic ridges have spread the ocean floor. 253

50.

Which of the tectonic plate is not a minor plate but is instead a major plate? A. Sunda plate B. Australian plate C. Philippine sea plate D. Somali plate

51.

The major and minor tectonic plates are mostly associated with land masses. Which plate is instead mostly underwater? A. Antarctic B. Eurasian C. Pacific D. Indian

52.

What plates are involved in the East African Rift seen in Kenya? A. African and Pacific B. Nubian and Pacific C. Somali and African D. Nubian and Indian

53.

Which mountainous area was not made by subduction processes? A. Andes B. Alps C. Balkans D. Sierra Nevada

54.

What is happening with regard to plate tectonics at the San Andrea fault in Western USA? A. Transform boundary with dextral motion B. Transform boundary with sinistral motion C. Convergence with subduction D. Divergent boundary

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55.

Island arcs are made from what geologic phenomenon? A. Volcano buildup at places of plate divergence B. Volcano buildup on upper half of oceanic convergence and subduction C. Volcano buildup at convergence without subduction D. Volcano buildup at continental convergence with subduction

56.

What plate tectonic measuring technique can help determine the speed and direction of ocean floor spreading events? A. Geodetic technique B. Geometric technique C. Seismic technique D. Paleomagnetic technique

57.

Which plate tectonics measuring technique uses GPS to make these measurements? A. Geometric measuring B. Seismology C. Geodesy D. Paleo magnetometry

58.

What element is the most common in the earth's crust? A. Carbon B. Iron C. Silicon D. Oxygen

59.

The mineral you have has certain characteristics. In describing a mineral's characteristics professionally, what is not one of those you'll list? A. Color B. Luster C. Chemical composition D. Cleavage

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60.

Which color is not a common color you'll see in quartz? A. Gray B. Blue C. Pink D. Yellowish green

61.

If you find a nice piece of olivine and turn it into a gem for jewelry, what gem would this create? A. Garnet B. Amethyst C. Opal D. Peridot

62.

What is not a distinctive feature of talc as a mineral? A. It is a hard mineral B. It is white in color C. It has a pearlescent luster D. It feels greasy when you touch it

63.

If a mineral is to fully form from an aqueous solution, what must happen? A. Evaporation B. Condensation C. Sublimation D. Aerosolization

64.

What are the pink crystals you see in granite? A. Quartz B. Biotite C. Potassium feldspar D. Plagioclase feldspar

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65.

Why is lava black and granite, which is also made from magma, not black? A. Lava has no mineral-making materials in it. B. Not enough pressure is involved in making lava. C. Lava is just one mineral. D. Lava has cooled much more rapidly.

66.

You are hiking in California and come across some tufa towers. What element are you sure to find in it as its main substance? A. Silicon B. Calcium C. Magnesium D. Sodium

67.

When you see a crystalline vein in a rock, what can you assume must have been involved? A. Water B. Hot gases C. Rapid cooling D. Sodium chloride

68.

You are describing the look of a diamond and decide it has what type of luster most likely? A. Vitreous B. Resinous C. Pearly D. Amantadine

69.

If you are describing a mineral as being resinous, what aspect of the mineral are you talking about? A. Its hardness B. Its luster C. Its density D. Its color 257

70.

What type of mineral might you have if it was found to set off a Geiger counter? A. Uraninite B. Magnetite C. Fluorite D. Calcite

71.

Which mineral among these is the hardest? A. Topaz B. Quartz C. Corundum D. Calcite

72.

What does the Vickers scale in geology measure? A. Mineral luster B. Mineral fracturing ability C. Mineral specific gravity D. Mineral hardness

73.

What does the Vickers test actually measure besides hardness in minerology? A. Resistance to pressure B. Density of a mineral C. Scratchability of a mineral D. Resistance to cleavage

74.

What most makes clays so easy and slippery to work with? A. The silicates break up more easily B. The silicates are made into sheets C. The silicates are unconnected to one another D. The silicates are mixed with sand

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75.

Biotite and muscovite are examples of what type of silicate? A. Mica B. Olivine C. Quartz D. Amphibole

76.

Which non-silicate mineral is made with iron and oxygen? A. Sylvite B. Cinnabar C. Hematite D. Galena

77.

What major element makes up the mineral substance in Epsom salts? A. Iron B. Copper C. Manganese D. Magnesium

78.

Which type of rock is usually rich in marine fossils? A. Granite B. Dolostone C. Halite D. Red sandstone

79.

What geologic mineral is behind ruby and sapphire gemstones? A. Hematite B. Fluorite C. Corundum D. Iron oxide

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80.

What happens in decompression melting to allow rocks to suddenly melt faster? A. Rocks dive deeper into the earth's core B. Rocks rise closer to the earth's surface C. Rocks get hotter as the temperature rises D. Rocks get ejected from a volcano

81.

When you have a flux heating phenomenon with rock melting, what happens to cause this? A. Rocks have water added to them. B. Rocks get pushed to the surface of the earth. C. Rocks are under a much greater pressure. D. Mixing of magma causes increased friction on the rocks.

82.

When magma cools, which component will crystallize first? A. Pyroxene B. Biotite C. Olivine D. Amphibole

83.

You have a mafic rock that cooled underground. What is it likely to be called? A. Basalt B. Gabbro C. Granite D. Andesite

84.

You see a fine specimen of felsic rock. What might it be? A. Granite B. Andesite C. Diorite D. Basalt

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85.

Your piece of granite has a lot of pinkish coloration in it. What element would account for this? A. Iron B. Potassium C. Sodium D. Sulfur

86.

In a magma chamber that cools, what will crystallize and fall to the bottom of the chamber first? A. Pyroxene B. Quartz C. Olivine D. Potassium plagioclase

87.

You see some rock called porphyritic rock. What best defines this rock? A. It is extrusive rock. B. It has a light density. C. It is mostly black. D. It has differing crystal sizes.

88.

Which stone is most likely a phaneritic igneous stone texture? A. Granite B. Basalt C. Obsidian D. Andesite

89.

Which stone of the igneous type is most likely called vitreous or glassy stone? A. Granite B. Basalt C. Obsidian D. Andesite

261

90.

From which type of igneous texture will you get large gemstones like garnets or sapphires? A. Phaneritic B. Aphanitic C. Vitreous D. Pegmatitic

91.

What is a pluton? A. An irregular piece of molten rock within another rock B. An upward plume of solidified magma C. A piece of hard olivine that solidified deep in the earth's core D. A piece of country rock that has melted

92.

What is a large sheet of sill that has deformed the rock layers in sedimentary rock called? A. Laccolith B. Xenolith C. Dyke D. Batholith

93.

At what level below earth's surface do diamonds get formed? A. 5 miles B. 20 miles C. 90 miles D. 300 miles

94.

If you were to find a diamond on the ground, where would you most likely look for one? A. Along the beach B. In a mid-continental stream C. Under the ocean ridges D. On top of mountains

262

95.

What part of the volcano's anatomy falls to the earth up to thousands of kilometers away? A. Lava flow B. Eruption column C. Pyroclastic flow D. Eruption cloud

96.

What part of the volcano's anatomy is ejected as a liquid but quickly solidifies? A. Lava bomb B. Lava flow C. Eruption column D. Side vent

97.

The stuff that comes off a volcano mixed with water and ash is called what? A. Pyroclastic flow B. Lahar C. Lava bomb D. Eruption cloud

98.

In a large eruption, what kills more people in general? A. Lahars B. Lava flows C. Pyroclastic flows D. Eruption clouds

99.

Which of the known volcanoes is not a composite volcano? A. Mount St. Helens B. Mount Fuji C. Mount Hood D. Mauna Loa

263

100.

What will you see in a composite volcano that you won't see in a cinder cone? A. Dykes B. Weathering C. Volcanic activity D. Ash formation

101.

What type of volcano is Mauna Kea in Hawaii? A. Composite volcano B. Cinder cone C. Shield volcano D. Lava dome

102.

Which volcano is the world's largest active volcano? A. Mount Etna B. Mauna Loa C. Mauna Kea D. Mount Kilimanjaro

103.

Which type of eruption would you most expect a lot of popping sounds when gas bubbles are released but not much damage? A. Hawaiian B. Strombolian C. Plinian D. Pelean

104.

Which type of eruption was Mount Vesuvius's eruption in 79 AD? A. Vulcanian B. Strombolian C. Plinian D. Pelean

264

105.

What eruption type was Mount St. Helen's in 1980? A. Vulcanian B. Pelean C. Hawaiian D. Plinian

106.

On the VEI scale of volcanic explosivity, what would you expect the VEI for a volcano like Kilauea in Hawaii to be? A. Zero B. Four C. Six D. Ten

107.

What type of volcanic eruption leads to tuya formation? A. Submarine B. Plinian C. Subglacial D. Surtseyan

108.

Which type of eruption is also called a steam-blast eruption? A. Submarine B. Phreatic C. Sub-glacial D. Strombolian

109.

What heralding event to a major volcanic eruption will be felt by grazing animals? A. B waves B. A waves C. Long-period waves D. Harmonic tremors

265

110.

What is not true of chemical weathering of rock? A. It is a rare phenomenon. B. It is a faster process when smaller rocks are acted on. C. It works on rock surfaces only. D. It turns rock into soluble ionic compounds.

111.

The process of hydrolysis in rock will take feldspar and turn it into what? A. Sand B. Clay C. Quartz D. Mica

112.

What factor least accelerates the dissolution of rocks? A. Warm weather B. Acidity C. Dry weather D. Biologic agents

113.

Oxidizing of metal accounts for some weathering situations in geology. What does oxidation do to weathering? A. It Increases the rate of weathering B. It decreases the rate of weathering C. It makes the rock more likely to form silicates D. It makes the rock more likely to turn into elemental iron

114.

What factor causes most of the mechanical weathering in the world? A. Wind B. Water C. Ice D. Gravity

266

115.

What least likely affects the rate of weathering of a rock? A. Nearby soil B. Temperature C. Moisture D. Air pressure

116.

What organisms help us use nitrogen by fixing it out of nitrogen gas? A. Algae B. Plants C. Bacteria D. Cyanobacteria

117.

Which layer of soil contains only the parent rock and nothing else? A. O horizon B. B horizon C. C horizon D. R horizon

118.

Some soil has an eluviation layer that is rich in what? A. Organic material B. Minerals C. Rocks D. Clay

119.

Which soil is mostly seen in the desert? A. Aridisols B. Mollisols C. Ultisols D. Vertisols

267

120.

Which soil would you most likely add to your garden to promote the healthiest garden because of its nutrient content? A. Loam B. Peat C. Silt D. Chalk

121.

Which soil type is not good for growing plants that need acidic soils? A. Chalk B. Loam C. Sandy D. Silt

122.

Which substance can be best mined in acidic soil and rock? A. Gold B. Silver C. Lead D. Zinc

123.

When sediment gets transported, which medium only transports ionic media and not solid media? A. Rivers B. Groundwater C. Wind D. Glaciers

124.

What is not a major function of transportation? A. Sorting B. Rounding C. Chemically reacting D. Moving

268

125.

What happens when you see depositional sorting in the process of sedimentation? A. Sand and clay get mixed together. B. Heavier items are deposited away from shorelines. C. Clay never comes out of suspension. D. Finer sediments settle out in calm deeper waters.

126.

A sedimentary rock that is mainly a lot of seashell material that has dissolved and then solidified is called what? A. Clastic B. Chemical C. Biochemical D. Organic

127.

How big does a boulder have to be at a minimum? A. 3 inches B. 10 inches C. 24 inches D. 35 inches

128.

You have sediment that settles out by size. Which size of clastic sediment is just a bit bigger than clay and will settle out just before it? A. Cobble B. Pebble C. Silt D. Sand

129.

What is not true about sorting of sediment when sedimentary rocks are being made? A. Stream sorting is usually uneven. B. Windblown sorting is uneven. C. Beaches sort out using higher energy than streams. D. Sorting depends on density and particle size. 269

130.

When looking for mature sedimentary rock, what would you see as a very mature type of sediment? A. Olivine B. Pyroxene C. Quartz D. Plagioclase

131.

You see a type of sedimentary rock that is filled with pink-colored feldspar as its main substance. What would you call it? A. Arkose B. Wacke C. Arenite D. Lithic sandstone

132.

What is the most common source of biochemical chert you'll see in biochemical sedimentary rock? A. Coral B. Crabs C. Diatoms D. Algae

133.

Which type of rock is not made from a type of silica chemical chert? A. Agate B. Diatomite C. Flint D. Jasper

134.

How long does it take to make one varve of sedimentary rock? A. A year B. 100 years C. 1000 years D. A million years

270

135.

What phenomenon would most likely cause hydrostatic metamorphism? A. Reservoirs B. Mountains C. Streams D. Waves

136.

If you see a foliated metamorphic rock, what will tell you that it is of this type? A. Pink coloration B. Large speckles of crystals C. Easy flaking D. Banded or layering

137.

You see a rock that is foliated and coarse-grained. It appears to be gneiss. What type of mineral will you see in it? A. Muscovite mica B. Feldspar C. Iron oxide D. Olivine

138.

What type of rock is jade? A. Green-colored quartz B. Green shale C. Green sandstone D. Green schist

139.

What type of substance do you get from limestone that is heat treated over time in contact metamorphism? A. Jade B. Marble C. Mica D. Amethyst

271

140.

Wollastonite is used in paints for its color. What is this metamorphic rock's color? A. White B. Red C. Pink D. Black

141.

Which type of metamorphic rock is the most coarse-grained among these? A. Slate B. Marble C. Schist D. Gneiss

142.

What feature will you see in injection gneiss that you won't see in other types of gneiss? A. It has alternating bands of igneous and sedimentary rock. B. It has a bright green color. C. It is mostly layers of different white quartz. D. It takes on iron oxide to have a bloodstone effect.

143.

Fuchsite quartz is a type of quartz that is contaminated with what contaminant? A. Copper B. Iron C. Chromium D. Zinc

144.

Hornstone is a hard rock that comes from what process? A. Heating quartz B. Heating shale C. Adding pressure to granite D. Adding pressure to limestone

272

145.

What is a common contaminant in dolomite that changes under conditions of metamorphism to become anorthite? A. Zinc compounds B. Sodium compounds C. Aluminum compounds D. Iron compounds

146.

Which mineral is not green in color and wouldn't necessarily be seen in green rocks? A. Chlorite B. Epidote C. Serpentine D. Iron oxide

147.

What is not true of foreshocks, mainshocks, and aftershocks? A. They occur at the same location as each other. B. The mainshock is the biggest shock. C. There is only one foreshock. D. Aftershocks can last for years after the mainshock.

148.

What statement is not true of a seismograph? A. It generally only picks up the main earthquake. B. It detects seismic wave activity of the crust. C. They are not very portable devices. D. It can record events over a period of time.

149.

What aspect of a given earthquake is variable in nature? A. Magnitude B. Fault length C. Intensity D. Duration

273

150.

When you see a sand blow, you know that what earthquake feature has happened to cause this phenomenon? A. Liquefaction B. Landslide C. Tsunami D. Ground shaking

151.

What earthquake phenomena are especially common in the Pacific basin area? A. Landslides B. Liquefaction C. Tsunamis D. Fault scarps

152.

Which waves on a seismograph are able to pass easily through the earth's mantle? A. P waves B. Love waves C. Raleigh waves D. S waves

153.

Which waves from an earthquake spread out in an elliptical fashion? A. P waves B. Love waves C. Raleigh waves D. S waves

154.

An earthquake in one year was 1.0 Magnitude points higher than in a previous year. How much stronger was the second earthquake? A. 5 times B. 10 times C. twice D. 100 times 274

155.

Below what magnitude level on the MMS will you not call it an earthquake at all? A. 10 B. 5 C. 3 D. 1

156.

What is not a factor used to determine earthquake intensity? A. Furniture damage B. Chimney damage C. Whether it is felt or not D. Dollar losses

157.

You are using triangulation to study an earthquake. What are you looking for? A. Whether or not a tsunami is coming B. The intensity of the earthquake C. The epicenter of the earthquake D. When the earthquake is coming

158.

What can be predicted in an earthquake? A. The magnitude B. The location C. The time it will happen D. The probability that it will happen

159.

There are different kinds of pressure on rock. Which type of pressure is represented by having a steady load of rock upon other rocks? A. Tensional stress B. Uniform stress C. Compressional stress D. Shear stress

275

160.

Which type of stress upon rock is said to stretch rock out? A. Tensional stress B. Uniform stress C. Compressional stress D. Shear stress

161.

Which type of stress on rock is most likely to twist rock in some way? A. Tensional stress B. Uniform stress C. Compressional stress D. Shear stress

162.

Where does the transition zone in the crust lead to more ductile behavior below this level? A. 1 kilometer B. 5 kilometers C. 15 kilometers D. 35 kilometers

163.

In measuring the dip and slip of an inclined plane, what statement is true? A. Water level is always set as horizontal if it's part of the inclination. B. The slip and dip are parallel to one another. C. The dip is set toward the north. D. The slip is the angle of the plane to the horizontal.

164.

If a dip of an incline is along the East-West line, what is the direction of the strike? A. East B. West C. South D. North

276

165.

You see a rock formation where there is a fault line. You stand on one side of the fault and see that the opposite side to your right has drifted downward or in the direction behind you. What is this called? A. Normal dip-slip B. Reverse dip-slip C. Right lateral strike-slip D. Left lateral strike-slip

166.

An extension fault area has had one block fall down with respect to another there is no uplift at the other end of the block. What would you call this? A. Graben B. Half-graben C. Horst D. Half-horst

167.

At what point in a geological fold with the folding pattern be most severe? A. Fold axis B. Hinge line C. Fold plane D. Limb

168.

In which type of folding pattern will you not be able to identify a true fold axis? A. Syncline B. Monocline C. Dome D. Anticline

169.

An extreme folding pattern in rock that looks like zigzags is called what? A. Chevron fold B. Overturned fold C. Asymmetric fold D. Recumbent fold 277

170.

Which type of mountains were neither created by folding of rock or fault thrusts? A. Himalayans B. Appalachians C. Cascades D. Sierra Nevadas

171.

What degree slope do you need to have a debris flow occur in most cases? A. 20 degrees B. 45 degrees C. 55 degrees D. 65 degrees

172.

In any landslide, what part will be nearest to the highest elevation? A. Zone of accumulation B. Zone of depletion C. Transverse cracks D. Crown

173.

Of the different types of mass movements, which one is more dangerous to larger areas and is also sudden in nature? A. Fall B. Topple C. Debris flow D. Slide

174.

Which type of mass movement involves a slope of fall that isn't an incline plane but is instead a concave surface? A. Translational landslide B. Rotational landslide C. Topple D. Debris flow

278

175.

What is the major factor leading to the development of a lateral spread of material in the earth? A. Steep slope B. Unstable bedrock C. Liquefaction D. Overhanging cliffs

176.

What factor makes a progressive flow last so long? A. They involve a lot of earth falling at once. B. They gain momentum over time as more stuff is picked up in the flow. C. They are just so imperceptibly slow that they last a long time without anyone noticing. D. They are usually sustained by repeated earthquake tremors.

177.

What factor does not lead to the development of an avalanche? A. Snowmobiles B. Skiers C. Snowstorms D. Loud sounds

178.

What is the major factor in snow deposition in a slab avalanche? A. Glacial melting B. Spring thaw C. Windy conditions D. Solar radiation

179.

In powdered snow avalanches, what is the main causative factor? A. Warmer temperatures B. Recent snowfall C. Seismic activity D. Windy weather

279

180.

What is the main associating factor linked to a lahar? A. Heavy rainfall B. Fracture of a rock wall C. Volcanic activity D. Extreme temperatures

181.

In an earth flow, what will most likely be seen at the leading edge of any surge of the flow? A. Mud B. Soil C. Water D. Boulders

182.

All water that you see in a stream comes from an area called what? A. Tributary B. Floodplain C. Mouth D. Basin

183.

What is an endorheic basin? A. A drainage area that ends in the ocean B. A drainage area that does not end in the ocean C. The end of a stream as it empties into a river D. The area around a river that floods seasonally

184.

What is the end of a stream called where it meets with a larger stream or river? A. Tributary B. Basin C. Mouth D. Delta

280

185.

Flow water in a channel in nature is termed what in geological terms? A. River B. Brook C. Creek D. Stream

186.

If you had to determine the thalweg of a stream, how would you find where it was at any given spot? A. You would measure the stream's width B. You would measure the bend in the stream C. You would measure how much water was flowing past that area D. You would find the deepest spot in the stream

187.

Studying drainage patterns of streams helps to understand regional geology. What pattern might you see if there were many subterranean caves or streams in a region? A. Rectangular B. Radial C. Deranged D. Dendritic

188.

As you study a stream, you plot its longitudinal profile. What will the graph be plotted like? A. Stream volume over time B. Stream volume over distance along the stream C. Stream elevation over distance D. Stream elevation over velocity

189.

You see an oxbow lake. What nearby feature caused that lake to appear? A. Volcano B. River delta C. Waterfalls D. Meandering river 281

190.

What would be the least factor weighing in on the size and shape of a delta? A. Water temperatures B. Wave action C. Tides D. Sediment

191.

Where will you find a speleothem in geology? A. On a mountaintop B. At the mouth of a stream C. In the water table D. In a cave

192.

What is not considered an example of karst? A. A lava tube B. A sinkhole C. A cavern D. A limestone tower

193.

The time it takes for adjacent water crests to pass at a given point in space or from one crest passing you to another is called what? A. Wave velocity B. Wave period C. Wave amplitude D. Wave trough

194.

Where do waves in the ocean come from in general? A. Underground currents B. Seismic activity C. Wind D. Volcanic activity

282

195.

What is the cause of a fjord? A. High waves B. Plate tectonic activity C. Limestone dissolution D. Glaciers

196.

What statement is not true of geothermal phenomena? A. They are evidence of magma close to the earth. B. They always occur near areas of volcanic activity. C. They involve some form of heated water. D. They can be dangerous.

197.

Which geothermal phenomenon involves flash steaming? A. Geysers B. Fumaroles C. Mudpots D. Hot springs

198.

What statement about glacier flow is not true? A. Glaciers flow the fastest at the bottom. B. Glaciers are rigid and more brittle at the top. C. Glaciers flow on a watery slide beneath them. D. Glaciers flow internally, despite being solid.

199.

What is not a major effect of global warming on glaciers? A. A decrease in glacier thickness B. A retreat of valley glaciers C. A retreat of the equilibrium line D. A decrease in calving

283

200.

A ridge between two glacial valleys is called what? A. Col B. Arete C. Tarn D. Cirque

284

ANSWERS TO QUESTIONS ANSWERS TO CHAPTER 1 1.

Answer: b. Pahoehoe is thick ropy lava that cools and folds into thick ropes.

Answer: c. Pumice is lightweight gas-filled and cooled lava that cooled so quickly that the gas is trapped in the rock.

Answer: a. Intrusions are crystallized areas of magma that arise as the magma cools.

Answer: d. Volcanoes are where magma comes up from the deeper areas of the earth in molten form in order to create new "rock" on earth.

Answer: c. Schist is the only one of these that is metamorphic. Foliation is the deformation of a rock's structural features in these types of rocks; it is due to pressure on the rocks.

Answer: b. Pyroclastic flow creates "pyroclastic", which is ash and gases that travel rapidly down the volcano’s side.

Answer: a. Shale is the rock that gets settled out of river deltas after water gets into still waters to create sediment that is grayish and that eventually forms into rock.

Answer: d. Plate tectonics involve the mass movement of large chunks of land. When they come together and squish land, this is what forms mountains.

Answer: c. Hydrolysis happens when acid rain falls to create a specific type of weathering in the rock.

10.

Answer: b. Metamorphic rock may have foliation as part of its features. This is the compression and pattern forming you see in rock that has been under pressure for a long period of time.

285

ANSWERS TO CHAPTER 2 1.

Answer: c. The earth is about 4.5 billion years old and formed from hot gases and dust existing in space.

Answer: d. Earth has been in the Precambrian era for about 88 percent of its geological time.

Answer: b. Archaea are a kingdom of single-celled organisms that are actually in their own kingdom altogether. These were the first organisms on earth.

Answer: c. The vast majority of the oxygen gas in our atmosphere came from the photosynthetic activity of the microorganisms existing from the Precambrian era.

Answer: b. The asthenosphere is like gelatin. It is semi-solid and helps to lubricate the crust as it moves along the mantle around earth.

Answer: d. The earth's mantle is made of an olivine mineral very similar to the gemstone known as peridot.

Answer: d. Crystallization is what you see when rocks solidify in the cooling process. This is basically what happens to magma.

Answer: a. The continental rise is where the continental slope has less steepness due to the action of falling sediment from the continental shelf.

Answer: a. The continental rise would mark the boundary between the continental crust and the oceanic crust.

10.

Answer: c. Magnetic changes in rocks were the first to prove the existence of continental drift.

286

ANSWERS TO CHAPTER 3 1.

Answer: c. Among the different increments, the eon is the longest of these.

Answer: d. This time was an era, coming from the Precambrian Eon.

Answer: a. Crinoids are similar to sea urchins or sea cucumbers. They were animals that looked like fans or flowers on a stalk.

Answer: d. The Permian extinction was a mass extinction event that ended this era. The causes of the extinction event were likely multifactorial.

Answer: b. The Cenozoic era was the last of the geologic eras.

Answer: c. The Quaternary period is the last period of the Cenozoic era.

Answer: c. Atoms with differing isotopes involve atoms that differ in their atomic weight. Neutrons do not change the charge on the atom, just its weight.

Answer: d. Stratigraphy by itself is relative. It's only when you combine it with magnetism that you can get some absolute dating out of it.

9. 10.

Answer: d. A coprolite is a fossil made of feces. Answer: b. A trace fossil is one that shows the animal's tracks or other movements and doesn't show much about its shape.

287

ANSWERS TO CHAPTER 4 1.

Answer: a. Meteorologists noted that the outlines of the righthand side of South America and the left-hand side of Africa were found to be the same.

Answer: c. Plate tectonics indicates that earthquakes generally occur along plate edges. These are often at the edges of continents or in oceanic waters.

Answer: c. The fastest plate moves at about 10 centimeters per year.

Answer: a. The Pacific plate was the largest at more than 100 million kilometers in total square area.

Answer: d. It is the phenomenon of convection that most creates the pattern of movement of the plates around earth. Convection is the circular heating and cooling pattern of magma.

Answer: a. Divergent boundaries are found on both land and ocean and represent the separation of plates.

Answer: d. Subduction usually means denser rock sinks below less dense rock. This means that the subducted area comes from oceanic crust so the mountains made are those nearer to the edges of a continental area.

Answer: c. Convergence with subduction of heavier oceanic crust is what cause continental arcs to occur with both earthquakes and volcanoes along the arc region.

Answer: d. You won't get volcanoes where two continental plates are converging because the crust is too thick to have any magma slip up through these regions.

10.

Answer: a. GPS has made it possible to detect movement within plates themselves, called intra-plate crustal movement.

288

ANSWERS TO CHAPTER 5 1.

Answer: b. Minerals must be each of these things; they are not always made from a single element, however.

Answer: a. A gemstone is used in jewelry-making. It is not always a mineral. Amber is a natural substance that is organic, so it is not considered a mineral.

Answer: b. Fluorite is a colored mineral that can be a range of colors. The distinguishing feature is that fluorite will fluoresce under UV light.

Answer: d. The longer time you have to work with, the larger your crystal will likely be. This is the most important factor in any crystal growth.

Answer: c. Iron in quartz makes it amethyst, which is purple in color. It does have other substances in it but the iron most causes the color change.

Answer: b. Real gold will have a golden streak, while iron pyrite or fool's gold will have a black streak.

Answer: c. The basic shape of a silicate molecule is a tetrahedral shape.

Answer: d. Each of these is a metal cation that can be found in silicates, except for lead, which isn't usually found as part of these molecules.

Answer: a. Most of the industrial ores are metal sulfides used to extract the actual metals in the sulfide ore.

10.

Answer: d. Steel is a metallic substance that is not natural. It is manmade and comes from iron and carbon.

289

ANSWERS TO CHAPTER 6 1.

Answer: c. Each of these is a major component of the earth's magma. Lead is not considered one of them.

Answer: d. Each of these affects the melting process of rocks except for sunlight, which doesn't play a role.

Answer: d. You need a lot of silica to get quartz and gabbro is relatively silicapoor rock.

Answer: c. Basalt is the same as gabbro but it cools more rapidly above ground. Both are silica-poor rocks.

Answer: b. Vesiculation involves bubbles in the stone that get trapped as the stone is being formed. This leads to frothy stone.

Answer: d. Felsic lava is thick and when it is gaseous, it will become explosive when it erupts.

Answer: c. A xenolith is a piece of rock that melted and fell into another piece of rock and got stuck there is called a xenolith. It looks different from the surrounding rock.

Answer: d. A sill is a sheet of magma that came up and sifted through sedimentary layers, solidifying in an igneous sheet.

Answer: d. Carbon is made into diamonds from extremes of heat and pressure at the same time.

10.

Answer: a. Almost all diamonds used for industrial purposes are created in a laboratory.

290

ANSWERS TO CHAPTER 7 1.

Answer: b. Volcanism existed on earth as soon as there was crust. This was at least 4 billion years ago.

Answer: c. Mount Etna is the oldest volcano on earth, estimated to be 350,000 years old.

Answer: a. A cinder cone is your basic volcano that is built up with a single event.

Answer: b. Composite volcanoes are sometimes referred to as stratovolcanoes. This is because they are layered.

Answer: d. Lava tubes are common in shield volcanoes because they have hot liquid lava and few gases so these tubes can form beneath already-made crust above it.

Answer: a. Composite volcanoes have andesite lava with more silica in the lava than you'll see with shield volcanoes.

Answer: a. Surtseyan eruptions involve the interaction of magma and water, usually in shallow waters.

Answer: b. Accretional lapilli might be free or imbedded in rock. These are spherical balls that collect in areas around Surtseyan eruptions due to the interaction of magma and water.

Answer: a. If the sulfur dioxide gas emissions are greater in the vicinity of a volcano, this is a heralding event for an upcoming eruption.

10.

Answer: c. Each of these is detectable with remote sensing and sometimes with triangulation of sensing devices except for underwater ground temperature, which usually requires boring a hole to measure the deeper temperatures.

291

ANSWERS TO CHAPTER 8 1.

Answer: d. You need to have water drift into existing rocks to have this kind of weathering. You also need to have alternating hot and cold weather. Dry weather is not necessary.

Answer: c. Rhizoliths are petrified tree roots that have begun to crack and weather rock. They become a petrified part of the rock itself.

Answer: c. Olivine will dissolve chemically much more readily than any of the others. This will not be seen in areas with a lot of weathering.

Answer: d. Chemical weathering differences between different types of rock cause caves and sinkholes typical of karst topography.

Answer: b. Andisols are soils that come from fresh volcanic activity. It is a productive soil for growing things.

Answer: a. The O horizon is the organic layer. It is essentially just decaying organic matter and not much else.

Answer: c. Spodosols are not fertile at all because they are too acidic to have good growth of plant materials.

Answer: d. Clay soils are very heavy and don't drain well. They hold nutrients but just can't drain in wet environments.

Answer: c. Aluminum is mainly mined from tropical bauxite rock found in many parts of the world.

10.

Answer: d. The sulfate part of iron pyrite must be leached out of the mineral in order to turn it into more usable iron stores.

292

ANSWERS TO CHAPTER 9 1.

Answer: a. Each of these is true except that most sedimentation happens after a rock has weathered itself into sediments.

Answer: d. Only sand and clay are considered fully weathered sediments.

Answer: b. Each of these is a good cementer in making sedimentary rocks. Only halite is not a good choice because it would dissolve too easily in water.

Answer: a. Clastic rock is your typical sedimentary rock that goes through all the various stages mentioned.

Answer: a. Conglomerate stone is not very well sorted, but is made from rocks of many different types in general.

Answer: d. Dolomite is a mixture of magnesium, calcium, and carbonate that forms as a biochemical sedimentary rock.

Answer: b. Mudstone is shale that has hardened and will not fragment like shale does.

Answer: d. Organic shale is a good source of petroleum, given enough time to create this type of product.

Answer: d. Calcite dissolves in just about a month when it comes in contact with slightly acidic water. Quartz takes about 34 million years to do the same thing.

10.

Answer: c. Garnierite is green and is a high source of nickel for mining.

293

ANSWERS TO CHAPTER 10 1.

Answer: c. Contact metamorphism is also called thermal metamorphism. It involves changes in rock due to intense heat.

Answer: b. Static metamorphism is caused by the weight of overlying rocks and high pressure that changes the rocks.

Answer: a. The pressure involved in making schist means that mica flakes are created. The rest of the rock is gray and black.

Answer: c. Sandstone comes from heating and compacting sandstone.

Answer: c. The metamorphic trend is to start with clay then go to slate, phyllite, and finally to schist.

Answer: b. Garnet is schist but it is high-grade schist made under higher temperatures than low-grade schist.

Answer: d. Marble is made of calcite, which is calcium carbonate.

Answer: a. Most granite metamorphism involves high pressure situations. This leads to flattening of the quartz crystals, which will be relatively obvious.

Answer: b. Quartzite can be seen in subduction zones but will also be seen elsewhere. The rest are almost always seen in subduction zone areas.

10.

Answer: a. Shock metamorphism like from a meteorite will cause tektite formation. This is a black, glassy rock that resembles volcanic glass.

294

ANSWERS TO CHAPTER 11 1.

Answer: d. Fewer tremors in a known earthquake zone often means that the friction has caused tension in the area to build up. When this tension is significant, a large earthquake is more likely to occur.

Answer: b. The epicenter is above the hypocenter, which is where the earthquake first originates.

Answer: d. There are synonyms you can use for fault scarp. A crack in the earth is one of these good synonyms.

Answer: b. Liquefaction is very bad for earthquake victims. Buildings can tip over or sink into the ground when this happens.

Answer: d. Almost no amount of ground shaking in an earthquake is harmful unless you are indoors or under some type of bridge or other infrastructure.

Answer: b. A seismogram is simple and reflects the movement of earth's crust versus time.

Answer: b. Surface waves are slower than P and S waves; of the two surface waves, Raleigh waves are the slowest.

Answer: d. The Richter scale was not appropriate for all earthquakes in the world and only really worked for Southern California earthquakes.

9. 10.

Answer: b. A magnitude of between 6 and 6.9 involves a strong earthquake. Answer: a. The MM or modified Mercalli scale is used to measure earthquake intensity in an area.

295

ANSWERS TO CHAPTER 12 1.

Answer: c. The term "force per unit area" is also called pressure. The more force is put into a small area, the higher is the pressure involved.

Answer: a. Strain is any change in the size or shape of a rock. It is what happens to rocks under some type of pressure.

Answer: c. Each of these is a relatively ductile rock type except for quartz, which is a brittle rock type.

Answer: b. The faster the strain rate, the lower is the ductile properties of a rock. The rock under these circumstances is more likely to fracture.

Answer: b. You will see ductile activity in any rock if you see twisted components within it. The rest of the statements are untrue.

Answer: a. A normal dip-slip fault is where a section has dipped below the level of another rock due to the effects of gravity. You can tell the difference by looking to see whether the rock has slid down another face.

Answer: d. An anticline is your classic arching series of folds that will form a ridge along an area that has gradually compressed.

Answer: a. A monocline will not be completely symmetric so that the axis of folding is not vertical with respect to the limbs.

Answer: d. A recumbent fold is a hairpin fold that has fallen or been pushed asymmetrically so that the entire fold is horizontal with respect to the earth.

10.

Answer: d. The Sierra Nevada mountains are created by faults that dipped and thrust to make these types of Fault Block mountains.

296

ANSWERS TO CHAPTER 13 1.

Answer: c. Each of these statements is true; however, many human factors can contribute to landslides, including nearby construction, roadwork, or poor farming techniques on hillsides.

Answer: b. Water in an area in excess amounts contributes most to a natural trigger for a landslide. Excess water can happen due to any number of natural phenomena.

Answer: c. The tips or the tips of the toes are the furthest point that debris has gotten after a landslide.

Answer: b. A crown crack is a point of tension on a crown area, where the landslide pulled on the crown prior to falling.

Answer: a. Progressive creep might not be noticeable but because the shear stress decreases, the flows momentum will increase over time.

Answer: d. Earthflows are moderately slow and are linked to fine sediment like clay, silt, and sand.

Answer: c. Friction creates heat and will cause each of these things. When heat is involved, the combination of events will decrease and not increase the shear stress.

Answer: a. While no landslide is 100 percent predictable, good information can be gotten to give a good idea of where a landslide is probable.

Answer: b. The bottom-most fracture on the falling slab is called the sauchwall.

10.

Answer: a. Wet snow avalanches are super-saturated with wetness of snow near the melting temperature of water. This is due to warmer temperatures.

297

ANSWERS TO CHAPTER 14 1.

Answer: a. Transpiration is what happens in plants when photosynthetic processes give off water vapor as a byproduct.

Answer: c. Sublimation is a situation where water goes from solid to gaseous phases, usually from ice or snow.

Answer: a. At the mouth of the channel near the ocean the stream velocity is the highest, even though it looks a lot like a lazy river at that point in time.

Answer: b. You can measure a stream size by the volume of water passing through a given area over a specific period of time.

Answer: a. If the streams fan out like a tree, this is dendritic. This is the most common pattern of drainage you will see.

Answer: b. Each of these is related to the fluvial process of erosion. The exception is saltation, which is related to transportation instead.

Answer: b. The capillary fringe marks the water table. Beneath this layer you have water you can get from a well.

Answer: c. The aquiclude layer is so impermeable to water that it cannot get through its pores.

Answer: c. The berm is usually dry. It is the part of the beach where sand is deposited and generally doesn't get disturbed by wave buildup.

10.

Answer: a. The rip current is where water finds a channel back to sea. Swimmers can get pulled out to sea in this type of current.

298

ANSWERS TO CHAPTER 15 1.

Answer: c. Glacial ice comes from compaction of perennial snow that remains year after year despite the effects of summer.

Answer: b. The Antarctic Ice Sheet Glacier is 2.5 miles thick at its thickest spot.

Answer: a. Calving is where a glacier breaks off parts of itself into the ocean to give rise to more icebergs in the oceans.

Answer: c. A tarn is a lake that was once a bowl carved out by the end of a glacier in a mountainside.

Answer: a. A medial moraine only happens if you have two glaciers merge at one spot. The medial moraine will run between the two merged glaciers.

Answer: b. A kettle comes from till left behind after an ice block forms its own depression in the earth.

Answer: d. An esker is a band of sediment that follows an under the glacier stream of long ago. It is long and snake-like because it follows a stream.

Answer: c. An erratic is a boulder left behind after a glacier has retreated.

Answer: b. Lake Agassiz was a proglacial lake formed at the edge of a large continental ice sheet called the Laurentide ice sheet.

10.

Answer: a. Each of these is a proglacial lake; Great Salt Lake is the remnant we have of Lake Bonneville.

299

ANSWERS TO COURSE QUESTIONS 1.

Answer: a. Fine-grained rock must have granules that are less than 0.1 mm in diameter.

Answer: d. The floodplain can be seen along the sides of a riverbed and is often the area that floods when the river levels are very high.

Answer: b. These are all changes that happen to metamorphic rocks. The exception is magnetic changes, which are least likely to happen.

Answer: c. The lithosphere is the outer crust and mantle of the earth that is the area of most concern for geologists.

Answer: b. Calcium carbonate is the main substance you find in seashells and in the shells of many other marine invertebrates. It gets incorporated into limestone.

Answer: c. A mineral crystallizes into a regular shape of some sort in rock.

Answer: a. Sandstone is made from layering of sandy substances in water or on land.

Answer: d. Oxidation actually oxidizes iron to make iron oxides that are basically what you call "rust". It's the same rust you see on cars.

Answer: a. Lahar is a mudslide that can happen along the slopes of a volcano. It is made from ash and water that forms mud that travels down to cause a great deal of property damage after an eruption.

10.

Answer: d. The shiny "golden" flakes you find in schist is called mica.

11.

Answer: b. Gabbro is the type of igneous rock that has the largest inclusions. It is made from basalt that cooled the slowest.

12.

Answer: c. Slow cooling of magma leads to large inclusions in the basalt after it has cooled.

300

13.

Answer: c. Gravity causes sediment to settle down in water or air. After it settles due to gravity, it condenses to form rock.

14.

Answer: b. An erratic is a rock or boulder that has been deposited a long way from its origins due to the actions of a retreating glacier.

15.

Answer: d. Pillow lava comes up from the seafloor to make lava that looks like pillows as it cools.

16.

Answer: a. Playa is the area in a desert that temporarily forms a lake but is mostly evaporates area of the desert.

17.

Answer: b. Water around earth helped it cool enough to solidify and to have water become liquified enough to fall onto the earth.

18.

Answer: a. Oxygen was actually not present in early earth. Carbon dioxide and water vapor were the most prevalent.

19.

Answer: c. Carbon dioxide is part of what made the limestone substance, which is mostly made from calcium carbonate.

20.

Answer: d. The first land on earth was likely black volcanic islands made from volcanoes that rose above the ocean surface.

21.

Answer: a. Pangaea is a supercontinent but so were all these others. Among them, Pangaea was the last of these continents to have developed in geological time.

22.

Answer: d. The lithosphere is where the earth's surface and deep rocks exist.

23.

Answer: c. The mantle is a part of the chemical layers of the earth but not a rheologic layer.

24.

Answer: a. The ocean floor has the thinnest crust and is where magma comes up to build more crust. Continental and mountainous areas have thicker crust.

25.

Answer: b. The mantle makes up a huge part of the earth's volume – about 84 percent of its total volume.

301

26.

Answer: a. Iron makes up the greatest substance of the earth's outer core. It is hot enough to be in molten form.

27.

Answer: c. The earth's outer core is the third major layer in. It’s dense and rotates at a different rate than the rest of the earth so it sets up turbulence to create our magnetic field.

28.

Answer: b. The core is made from a great many heavy metals. Sodium is a light metal so it would not likely be in that dense part of the earth.

29.

Answer: c. Volcanoes erupting from the floor of the ocean created the seamounts as areas of a hotbed of volcanic activity.

30.

Answer: b. The biogenous contribution to the ocean floor sediment comes mainly from seashells.

31.

Answer: c. Ontario is a good spot for Precambrian rock because it is where the Canadian shield is located. It extends across the eastern half of Canada but only in the extreme northern regions of Minnesota and Michigan.

32.

Answer: a. The crust at the time was solid but the plates were thinner and the magma was hotter, meaning that they floated around more rapidly than they do now.

33.

Answer: d. Eukaryotes are larger than bacteria or prokaryotes. They have chromosomes, can be multicellular, and can reproduce sexually. They are not necessarily photosynthetic.

34.

Answer: b. Each of these was likely a factor in the development of snowball earth. The earth's tilt was the same as it is now, however.

35.

Answer: c. Mollusks were the first among these fossils you can see when looking at rocks from the Paleozoic era.

36.

Answer: b. Many of the known early arthropods were extremely large. It may have been due to high oxygen levels or lack of predators.

37.

Answer: c. The Silurian period was from the earlier era – the Paleozoic. The other three represented the Mesozoic era.

302

38.

Answer: a. This was the age of the dinosaurs, especially during the Jurassic and Cretaceous period.

39.

Answer: d. An impact from a giant asteroid likely caused this mass extinction, killing the entire dinosaur population.

40.

Answer: a. Carbon dating would not be helpful to dating rocks as much because it only dates back to about 50,000 years.

41.

Answer: b. Each of these is a known principle of stratigraphy except for laterality, which is not one of these principles.

42.

Answer: d. A cross-cutting layer spans other layers and would often be diagonal to them, representing a younger layer that laid down on a fault or crack across other layers.

43.

Answer: a. Each of these is a key feature of an index fossil except that it usually must have lived over a short time span in geologic time.

44.

Answer: a. Radiocarbon dating is not as helpful as other dating methods because carbon decays fast enough to have all the carbon 14 made during the time when an organism was living to become carbon 12 within about 70,000 years.

45.

Answer: b. Potassium argon dating is not one based on crystals at all but is based on isotope decay.

46.

Answer: d. Uranium is unstable and is radioactive, giving off electrons that can be detected in Geiger counters or trapped in crystal imperfections.

47.

Answer: c. Amber is simply hardened and petrified tree sap that can trap body fossils.

48.

Answer: b. Bathymetry or the study of ocean depths was able to be used to determine that the oceans have mid-oceanic ridges where the oceanic floors are spreading and adding new crust to these areas.

49.

Answer: d. The magnetic striping shows differences in the earth's polarity, with ocean floor growing at times when the polarity has shifted.

303

50.

Answer: b. Each of these is considered a minor plate except for the Australian plate, which is a major plate.

51.

Answer: c. The Pacific plate is large and covers the majority of the Pacific Ocean.

52.

Answer: c. The African plate is also called the Nubian plate. Along the rift in East Africa, you have the Somali plate separating from the Nubian or African plate.

53.

Answer: b. Each of these was made by a convergent/subduction process except for the Alps, which were not made by any subduction process – only a convergent one.

54.

Answer: a. The San Andreas fault maintains its earthquake activity due to it being a transform boundary with dextral motion.

55.

Answer: b. Island arcs are areas of convergence and subduction in the ocean with volcano formation on the upper half of the convergent area.

56.

Answer: b. The geometric technique studies the divergent zone treads and plugs this information into mathematical formulas to get information on speed and direction of plate movements.

57.

Answer: c. Geodesy uses GPS to measure all the parts of the globe using stable satellite imagery that is extremely accurate.

58.

Answer: d. Oxygen is the most abundant element in the earth's crust, followed by silicon.

59.

Answer: c. When describing a mineral, you would use all of these characteristics. The chemical composition is important chemically but not geologically.

60.

Answer: b. Quartz is often named differently depending on its colors. The color blue is not a common color for this mineral.

61.

Answer: d. Olivine is basically a raw and sometimes much uglier form of peridot. Gem-quality olivine is made into peridot jewelry.

304

62.

Answer: a. Talc has each of these features except that it is a very soft mineral in general.

63.

Answer: a. You need to have the water evaporate in order for the mineral to make its appearance.

64.

Answer: c. Potassium feldspar is the pinkish crystal you'll see in granite. The rest of these minerals also exist in granite.

65.

Answer: d. Lava has cooled so much more rapidly than granite so that crystals, if they exist, are too small to be seen.

66.

Answer: b. Tufa towers are made from calcium carbonate that precipitates in alkaline waters before the water evaporates away.

67.

Answer: a. Veins in rocks that contain crystals usually mean water has seeped through a crack and the minerals in there were left over when the water evaporated or left.

68.

Answer: d. The term "amantadine" means sparkly. Diamonds most often have an amantadine luster.

69.

Answer: b. The luster is used to describe how a mineral reflects light. The term resinous describes a particular luster to the mineral.

70.

Answer: a. Uraninite is a mineral that has uranium in it. It will be radioactive when you test it with a Geiger counter.

71.

Answer: c. Among these choices, corundum is the hardest one.

72.

Answer: d, Mineral hardness is measured by both the Vickers and hardness scale.

73.

Answer: a. The Vickers test uses the resistance of a mineral to pressure as a way of determining its hardness.

74.

Answer: b. The silicates are made into sheets that are separated by water before they are dried in a kiln.

75.

Answer: a. Both biotite and muscovite are examples of mica.

305

76.

Answer: c. Hematite is an ore made from oxygen and iron, similar in chemical formula to magnetite.

77.

Answer: d. Magnesium sulfate is the major component of Epsom salts.

78.

Answer: b. Dolostone and limestone are extremely high in marine fossils. These are good places to look for ancient marine fossils.

79.

Answer: c. Corundum is simply an aluminum oxide-containing mineral that is the base molecule for making rubies and sapphires.

80.

Answer: b. Decompression melting happens when the rock material gets closer to the earth's surface, meaning that the decrease in pressure on it helps the rock melt even if the temperature hasn’t changed much.

81.

Answer: a. Flux heating involves added water to the mantle, which lowers the temperature the rock needs to heat. This leads to melting of the rock.

82.

Answer: c. Olivine crystallizes first and then it becomes pyroxene as the magma cools further.

83.

Answer: b. Gabbro is mafic rock that essentially cooled underground. Expect to see more black than any other color.

84.

Answer: a. Granite is a typical felsic rock.

85.

Answer: b. The pink in granite is due to its potassium feldspar in it. This feldspar is high in potassium as a major element.

86.

Answer: c. Olivine will crystallize first in a hot magma chamber. This gives rise to less olivine in the molten mixture; what remains is going to be more felsic.

87.

Answer: d. Porphyritic rock is that which has widely differing crystal sizes.

88.

Answer: a. Granite has visible crystals so it will be called phaneritic stone.

89.

Answer: c. Obsidian is glassy or vitreous. It has few crystals and is very dense.

90.

Answer: d. Pegmatitic rocks crystallize so slowly that very large crystals or gemstones can form within the rock.

306

91.

Answer: b. An upward plume of solidified magma that did not reach the earth's surface but solidified before that is called a pluton.

92.

Answer: a. A laccolith is a sheet of igneous sill that is so thick, it deformed layers of sedimentary rock between the layers as it cooled.

93.

Answer: c. The diamond stability zone is about 90 miles beneath the earth; it is hot enough there with plenty of pressure to allow diamonds to form in magma.

94.

Answer: b. You can find diamonds that have weathered off streams and rivers in the mid-continental regions, where the crust is deep enough to have diamonds form in the first place.

95.

Answer: d. The eruption cloud is the ash that falls from the sky after the eruption column spews out. It is able to fall ash to the ground many kilometers away from the volcanoes themselves.

96.

Answer: a. A lava bomb is ejected as a ball of liquid out of the lava vent but is solidified as an extrusive lava rock.

97.

Answer: b. The lahar is a mudslide made from volcanic material plus water that flows away from the volcano to cover large areas of territory.

98.

Answer: c. Pyroclastic flows are very deadly to people in the vicinity of the volcano because of the speed and heat involved in these flows.

99.

Answer: d. Mauna Loa is a shield volcano, while the rest are all composite volcanoes.

100.

Answer: a. You will see many more dykes on composite volcanoes because they have side vents that allow for lava or magma dykes to form and solidify.

101.

Answer: c. Mauna Kea and Mauna Loa are both shield volcanoes.

102.

Answer: b. Mauna Loa is the world's largest volcano. Mauna Kea is bigger but is not active so it doesn't count.

103.

Answer: b. Strombolian eruptions are noisy but not very dangerous in general.

307

104.

Answer: c. Mount Vesuvius was an eruption of the Plinian type. It was an extremely dangerous eruption.

105.

Answer: d. The eruption of Mount St. Helen's was a Plinian eruption because of the high plume and gas ejected from this destructive volcano.

106.

Answer: a. The VEI scale only goes from 0 to 8. The Hawaiian eruption from Kilauea has a VEI scale number of zero.

107.

Answer: c. Subglacial eruptions lead to interesting flat tops and steep sides called tuyas as part of the eruption.

108.

Answer: b. Phreatic eruptions are essentially steam-blast eruptions that break rock but don't really eject any new magma.

109.

Answer: d. Harmonic tremors are felt as vibrations in grazing animals indicating an upcoming volcanic reaction.

110.

Answer: a. Rock weathering using chemical phenomena is extremely common and not rare at all. The other statements are true.

111.

Answer: b. The process of hydrolysis in geology will take feldspar and break it down into clay particles, which are much finer sedimentary pieces.

112.

Answer: c. Acidity most accelerates the dissolution of rocks, so things like acid rain will make this process more prevalent overall. Dry weather does not promote rock dissolution.

113.

Answer: a. Oxidation makes a rock more likely to wear away through weathering.

114.

Answer: b. Water is the main factor causing most of the erosion on earth. The other choices still play a role in mechanical weathering.

115.

Answer: d. Each of these has a major effect on the rate of weathering except for air pressure, which has less of an effect.

116.

Answer: c. Nitrogen-fixing bacteria will fix nitrogen out of gas so that plants and animals can use them.

308

117.

Answer: d. The R horizon is rocky and contains only the parent rock. It is the deepest layer of soil.

118.

Answer: b. The eluviation layer is rich in minerals because it has had water in the upper layers wash the minerals into it.

119.

Answer: a. Aridisols are those that are seen in deserts or in arid regions. They are not very fertile.

120.

Answer: b. Peat is often added to a garden to boost its nutrient counts and promote a better growing environment for plants.

121.

Answer: a. Chalk soil is alkaline and sometimes can't be acidified enough to grow certain plants.

122.

Answer: a. Gold is the only one of these that can be mined in acidic rock and soil. The others are not very easily mined under these circumstances.

123.

Answer: b. Groundwater is what transports a lot of ions but not solids as it is hard to get solids to sift through places underground that ions can get into easily.

124.

Answer: c. Transportation does each of these things but it doesn't do a good job of chemically reacting rocks when they are transported.

125.

Answer: d. When depositional sorting happens, the finer sediments stay in suspension and settle out in calm, deeper waters.

126.

Answer: c. Biochemical sedimentary rock comes from dissolved bones and/or seashells that later precipitate out of water.

127.

Answer: b. A boulder must be at least 10 inches in diameter to be called a boulder.

128.

Answer: c. Silt is just a tiny bit bigger than clay but is still less than 1/16th of a millimeter.

129.

Answer: b. Each of these is a true statement about sorting of sediment except that windblown sorting is usually even due to the high energy involved.

309

130.

Answer: c. Quartz is the most mature type of sediment you can get in sedimentary rock.

131.

Answer: a. Arkose is made of potassium feldspar so it is pink and has sedimentary features.

132.

Answer: c. Diatoms die off and give rise to calcium-containing biochemical chert that settles down in water and becomes sedimentary rock.

133.

Answer: b. Each of these is silica chert with some impurities to give them different coloration patterns.

134.

Answer: a. One varve represents a year's worth of lake sediment, including summer and winter.

135.

Answer: a. Reservoirs with a lot of weight on them will have hydrostatic metamorphism happen to them.

136.

Answer: d. Foliation means that a rock has gotten squished so that there will be layering of the rock.

137.

Answer: b. Feldspar is a rock type that makes up most of the gneiss you see.

138.

Answer: d. Jade and jadeite are both green schist that is prized mainly for the green color.

139.

Answer: b. Limestone that is treated over time with heat will become the white marble you see in statues, etc.

140.

Answer: a. Wollastonite is a bright white color used to make white paint, among other things.

141.

Answer: d. Gneiss is coarse grained and sometimes banded to make its texture.

142.

Answer: a. Injection gneiss is mostly layers of igneous and sedimentary rock that alternate with one another.

143.

Answer: c. Fuchsite quartz is green because of chromium being its main impurity.

310

144.

Answer: b. When you heat shale excessively, it bakes into hornstone, which is a gray, hard rock.

145.

Answer: c. Aluminum compounds are common contaminants in dolomite. The end result of metamorphism becomes anorthite.

146.

Answer: d. Iron oxide is not green; it is red. The others are all green minerals.

147.

Answer: c. There can be more than one foreshock before the mainshock happens; aftershocks can happen for a long time afterward.

148.

Answer: a. Seismographs will pick up all detectable seismic activity – not just the mainshock or main earthquake.

149.

Answer: c. These are all fixed with respect to a given earthquake but the intensity varies with the location a person is with respect to the epicenter.

150.

Answer: a. Liquefaction causes vents in the earth to emit sand particles in large numbers so it looks like a small sand volcano or sand blow.

151.

Answer: c. Tsunamis are common to the Pacific basin area because they occur when there is vertical shifting of two earth segments. This is not seen in California or other types of slip-fault type earthquakes.

152.

Answer: a. Only p waves are easily able to pass through the earth's mantle the entire way.

153.

Answer: c. Raleigh waves are surface waves that spread out in an elliptical fashion so they spread far and long after the main earthquake is over.

154.

Answer: b. The scale is logarithmic so a 1.0 point increase means that the second earthquake would be 10 times stronger than the first.

155.

Answer: c. A level below 3.0 is not called an earthquake at all.

156.

Answer: d. The intensity is based on a number of things. It is not usually based on the dollar losses in an earthquake.

157.

Answer: c. Triangulation is used to determine where the epicenter of an earthquake was. It requires three seismographs at three different locations.

311

158.

Answer: d. Earthquake predictions can only go as far as saying the probability that an earthquake will happen within a few years.

159.

Answer: b. Uniform stress is the type of steady pressure you get when heavy rock is set upon other rock. Compressional stress is similar but is not uniform in nature.

160.

Answer: a. Tensional stress is the type that involves stretching of rock compared to its original position.

161.

Answer: d. Shear stress involves slippage that will most contribute to the twisting of rock in some way.

162.

Answer: c. At 15 kilometers beneath the earth's crust, there is a transition zone where rock is more ductile below this level.

163.

Answer: a. When water is involved in an inclination, such as when an incline sticks out of the water, the water level is always set to the horizontal.

164.

Answer: d. The strike direction will be the direction of the plane of the inclined rock face. If the dip direction is east to west, the strike direction will be north as this is a compass direction.

165.

Answer: c. This is a right lateral strike-slip because the side traveling to your right is in the 6 o-clock position or behind you.

166.

Answer: b. A half-graben involves a fault that has a section sliding down with respect to another in such a way as to tip the fallen block rather than have it fall down horizontally. This is a half-graben.

167.

Answer: b. The hinge joint will represent the most severe folding of the rock in any hinge.

168.

Answer: c. A dome would not really have a hinge. This means that you could not really calculate any real fold axis.

169.

Answer: a. A Chevron fold looks like zigzagging as the limbs are bend up and down like an accordion under extreme stress.

312

170.

Answer: c. The Cascades are volcanic mountains, which are made from magma and not from a lot of plate tectonic, fault-breaking, or ductile activity.

171.

Answer: a. A 20-degree slope is what you need to have any significant debris flow to happen.

172.

Answer: d. The crown is the uppermost part of the landslide, where the landslide earth comes from. It is at the highest elevation.

173.

Answer: d. Slides are sudden mass movements involving larger volumes of slope that fall at one time; these are very dangerous.

174.

Answer: b. A rotational landslide is where the slope that remains is concave, which means it is spectacular when it happens.

175.

Answer: c. Lateral spread does not need much slope. The major problem is liquefaction and a lack of cohesion of the material that just spreads out on a minimal slope.

176.

Answer: b. These flows last a long time because they pick up more debris and gain momentum so it takes more to stop them.

177.

Answer: d. Many people believe that loud sounds contribute to avalanches but this is not true at all.

178.

Answer: c. Windy conditions cause the deposition of a slab of snow that falls in a slab off a mountains side.

179.

Answer: b. A recent snowfall of powdery and dry snow will be the main causative agent in these types of avalanches.

180.

Answer: c. A necessary feature of a lahar is volcanic activity but it doesn't have to be recent. Lahars are a slurry of volcanic material and water.

181.

Answer: d. Large boulders and sometimes logs will be dense and will be at the leading edge of the surge.

182.

Answer: d. A basin or catchment is the area of landscape that drains water from all sources into the same stream.

313

183.

Answer: b. An endorheic basin is one that does not end in an ocean.

184.

Answer: c. The mouth of a stream is where the stream ends and meets with a larger stream or river. It will discharge into this other river or stream at the mouth.

185.

Answer: d. In geology, everything is termed a stream, even if it is conventionally called something else.

186.

Answer: d. The deepest spots along the course of the stream is the thalweg. At any spot, you find where the thalweg line would be at that point.

187.

Answer: c. Deranged patterns are seen when there are places for water to disappear and reappear in random patterns that are not as predictable as others.

188.

Answer: c. The longitudinal profile of a stream is its elevation versus the distance along the stream.

189.

Answer: d. A meandering river or stream can be so extreme that a part gets cut off and forms a lake called an oxbow lake.

190.

Answer: a. A delta is formed by sediment; it is shaped by the tides and wave action outside the mouth of the stream.

191.

Answer: d. A speleothem is a stalagmite or stalactite found in caves. These are deposits of calcite after it has leached through the earth.

192.

Answer: a. A karst must involve the dissolution of limestone and be a geological feature of that. A lava tube is a geological feature that is not karst because it does not involve this process.

193.

Answer: b. The wave period is a timed measurement, where you measure the time it takes for adjacent wave crests to pass over a given point on the water surface.

194.

Answer: c. Waves in the ocean come from the action of wind against the water. This leads to friction and the development of waves.

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195.

Answer: d. Fjords are caused by glacial action that cut out these areas during an ice age. Then the sea level rose to create the watery fjord.

196.

Answer: b. These statements are true, except that they do not have to be near volcanic activity to be present.

197.

Answer: a. Geysers involve complex plumbing below ground and flash steaming of water. The steam pushes water up out of the earth.

198.

Answer: a. Glaciers flow the fastest in the middle with the top of the glacier getting dragged with it.

199.

Answer: d. Each of these is an effect of global warming except for a decrease in calving. In actuality, there is an increase in calving with global warming.

200.

Answer: b. An arete is a ridge formed by two adjacent valleys that were carved out by glaciers.

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College Level Geology

Articles inside

Course Questions

Chapter 15: Questions and Answers

Summary

Key Points in this Chapter

Glacial Lakes

Landforms caused by Glaciers

Chapter 14: Questions and Answers

Key Points in this Chapter

Geothermal Features

Coastlines

Hydrology-based Earth Features

Channel Types in Streams

Surface Water Explained

Fluvial Processes

Sediment in Streams

Water Basins

Chapter 13: Questions and Answers

Avalanches

Earth Flows

Key Points in this Chapter

Can Landslides be Predicted?

Types of Landslides

Chapter 12: Questions and Answers

Rock Folding

Folding and Mountain Building

Key Points in this Chapter

Faults and Joints

Strike and Dip Explained

Ductile versus Fragile Rock

Chapter 11: Questions and Answers

Earthquake Predictions

Earthquake Measurements

Measuring Magnitude of an Earthquake

Key Points in this Chapter

Metamorphic Environments

Earthquake Features

Conditions of Metamorphism

Marble

Schist

Gneiss

Non-clastic Rocks

How Sedimentary Rocks are Structured

Key Points in this Chapter

Detrital Sedimentary Rocks

Naming Sedimentary Rocks

Sedimentary Rock Basics

Chapter 8: Questions and Answers

Key Points in this Chapter

Soil Orders

Basic Soil Types

Ore Deposits and Weathering

Soil Formation and Classification

Soil

Wind and Desert Features

Weathering Rates

Chapter 7: Questions and Answers

Types of Chemical Weathering

Key Points in this Chapter

Volcano Seismology

Lava Flows and Pyroclastic Flows

Types of Volcanoes

Volcano Anatomy

Key Points in this Chapter

Diamonds and their Origin

How to Name Igneous Rocks

Intrusive Igneous Rock

Igneous Textures

Silicates in Igneous Rock

Key Points in this Chapter

Nonsilicate Minerals

How Magma turns to Rock

Classifying Minerals

More on Silicate Minerals

How Minerals Form

Chapter 4: Questions and Answers

Key Points in this Chapter

Measuring Plate Motion

Examples of these Phenomena in Geology