Preview Cambridge IGCSE Geography Revision Guide by Cambridge International Education

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Cambridge IGCSE®

Geography Revision Guide Second edition

David Davies

Original material © Cambridge University Press 2017

Table of contents

Introduction iv v How to use this book Theme 1: Population and settlement 7 8 Chapter 1: Population dynamics Chapter 2: Migration 19 26 Chapter 3: Population structure Chapter 4: Population density and distribution 33 Chapter 5: Settlements and service provision 43 Chapter 6: Urban settlements 50 Chapter 7: Urbanisation 58 67 68 83 97 108 115

Theme 3: Economic development Chapter 13: Development Chapter 14: Food production Chapter 15: Industry Chapter 16: Tourism Chapter 17: Energy Chapter 18: Water Chapter 19: Environmental risks of economic development Chapter 20: Geographical skills (Paper 2) Chapter 21: Alternatives to coursework (Paper 4)

127 128 138 148 155 162 172 183 192 205

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Theme 2: The natural environment Chapter 8: Earthquakes and volcanoes Chapter 9: Rivers Chapter 10: Coasts Chapter 11: Weather Chapter 12: Climate and natural vegetation

Answers 211 Index 234

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Introduction This guide has been written to help you revise for your Cambridge IGCSE Geography examination. The chapters follow the order of the topics and papers in the Cambridge IGCSE syllabus. • definitions and explanations of key terms • tips to provide helpful guidance on key points • self-test questions to allow you to test your understanding • interesting facts for additional information

Each chapter includes:

• sample questions and answers to highlight common mistakes or misunderstandings

• sample examination-style questions for your practice – with sample answers at the back of the guide. Revision and exam techniques play a major part in your level of success in an examination, so remember to start your revision well before the actual examination. Use several short sessions to help build up your knowledge of the subject, over a period of time, so that you do not leave too little time to digest and understand the information.

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Apart from reading through the text, leave yourself time to attempt the questions. This is also a good method of revision and it allows you to do something practical rather than just reading. It may also be useful for you to make your own summary of the topics as you work through them – this can be done on postcard-sized cards to allow you to quickly reference the information.

Cambridge IGCSE Geography assessment All students will take Paper 1 and Paper 2 and then either carry out Coursework for Paper 3 or do the Written Paper 4 – Alternative to Coursework. You should check the syllabus for the year that you are taking the paper for examination information and details of the individual papers.

Command words

All exam questions ask you precisely what they want you to do and to answer. To make this as precise as possible, they will use command words in their questions. It is important to fully understand the meaning of these words in order to answer a question correctly. There are two very simple instructions to follow when doing the exam, i.e., RTQ and ATQ – Read The Question and Answer The Question.

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learning summary By the end of this chapter, you should be able to: describe the main types and features of volcanoes and earthquakes, including the types of volcanoes (such as strato-volcanoes and shield volcanoes)

explain what can be done to reduce the impacts of earthquakes and volcanoes demonstrate knowledge of case studies of an earthquake and a volcano.

describe and explain the distribution of earthquakes and volcanoes, including the global pattern of plates, their structure, and an awareness of plate movements and their effects

demonstrate an understanding that volcanoes present hazards and offer opportunities for people

Chapter 8

Earthquakes and volcanoes

describe the causes of earthquakes and volcanic eruptions and their effects on people and the environment

8.1 The main types and features of volcanoes

1 Where two tectonic plates move away from each other – i.e. the plates diverge, at constructive/ divergent boundaries, and a gap/line of weakness is created in the Earth’s crust. Molten magma emerges through the gap. When magma appears on the Earth’s surface, it is called lava. The lava solidifies to form a volcano.

2 Where two plates move towards each other – i.e. the plates converge at destructive/convergent boundaries, where a heavier, denser oceanic plate moves down under a less heavy continental plate (the process of subduction). Friction and intense heating will take place, which results in the destruction of the oceanic plate, causing the rocks in the plate to melt and turn into molten magma. The build-up of magma creates enormous pressures on the crust above it and the magma rises through lines of weakness to emerge on the surface of the Earth. The lava then solidifies to form a volcano.

TERMS

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A volcano is a landform, often the size of a mountain or hill, typically conical in shape, having a crater or vent through which lava, rock fragments, hot gases and steam are, or have been, erupted through the Earth’s crust. Volcanoes normally form in three possible types of location:

3 Some volcanoes form over thinner, weaker areas towards the centre of a tectonic plate, called hot spots. At these weak spots, magma can force its way to the surface to form a series of volcanoes, such as the Hawaiian Islands. volcano: cone-shaped mountain formed by eruptions of lava at the surface of the Earth crater: a depression on the surface of a volcano, formed by volcanic activity, often circular in shape with steep sides vent: the natural pipe or fissure that links the magma chamber to the crater or opening on the Earth’s surface through which lava, ash and gases flow lava: magma that has escaped from beneath the Earth’s crust and has flowed onto the surface tectonic plates: huge pieces of the Earth’s crust that float and move on top of the much denser mantle below them constructive/divergent plate boundary: where two plates move apart, allowing magma to come to the surface as lava. magma: molten rock found beneath the Earth’s crust

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hot spot: a central part of the Earth’s crust where plumes of magma rise to the surface

• lahars: melted snow and ice from the top of the volcano combined with rainwater, which mixes with ash and runs off the volcano, flooding valleys and flatter areas surrounding the volcano with mud • earthquakes: as the magma moves upwards, the enormous pressure on the crust reaches breaking point, causing violent shaking (see Section 8.2).

Apart from lava, the magma may come out on to the Earth’s crust in a two other ways:

• pyroclastic ﬂows: clouds of very hot, poisonous gases mixed with ash that flow down the sides of volcanoes at speeds up to 200 km per hour

subduction: when one plate sinks below another

Some volcanic eruptions are also accompanied by:

1 It may explode out and fall as volcanic bombs. Fragments of molten rock between 60 mm and 5 m in diameter are ejected into the air; they cool into solid fragments before they reach the ground up to 5–600 m from the vent.

The main features of a volcano are shown in Figure 8.1.

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2 It may appear as very fine ash – fragments of pulverised solid lava, measuring less than 2 mm in

Over time, varying from a few weeks to several thousand years, all this ejected material may build up to form a volcano.

FACT

TERMS

destructive/convergent plate boundary: where two plates move towards each other

diameter. Once in the air, ash can be transported by wind up to thousands of kilometres away.

8 Earthquakes and volcanoes

Magma chamber: a large natural underground chamber of magma found within the surface of the Earth beneath a volcano.

ash cloud

ash fall + acid rain

ash fall

ice and snow

volcanic bombs

lava dome collapsed

pyroclastic flows

s flow lava

lahars

earthquakes caused by pressure of magma movement (shown with X)

s fl

landslide

X X

X fumaroles

X X

cks

cra

magma chamber

ground water

Figure 8.1 Main features of a volcano

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layers of ash

lava

1 Composite or strato-volcanoes: these are made from alternating layers of lava and ash as both come out of the vent during an eruption (Figure 8.2). They form on destructive plate boundaries where oceanic crust has melted as it is subducted. The lava forces its way up through the crust and emerges as a violent explosion. An example is Mount Etna in Sicily, Italy.

3 Dome volcanoes: these are also made from lava but the lava is acid and thicker and cools quickly. It does not flow very far before becoming solid, and so these volcanoes are steep-sided and high (Figure 8.4). An example is Mount St. Helens in the USA.

lava

Theme 2: The natural environment

There are three main types of volcano based on their shape and what they are made of.

magma chamber

Figure 8.2 a composite volcano

You do not need to revise dome volcanoes, but they are included here to give a complete understanding of volcanoes.

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2 Shield volcanoes: these are made from lava and form on constructive plate boundaries or at hot spots, such as Mauna Loa in Hawaii. They form large volcanoes, with gently sloping sides, sometimes hundreds of kilometres across because the lava is alkaline and very runny and travels a long way on the surface before cooling and solidifying (Figure 8.3).

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Figure 8.4 a dome volcano

Volcanoes can be active, dormant or extinct: • An active volcano is one that has recently erupted and is likely to erupt again. There are about 1700 active volcanoes in the world today (Figure 8.5). • A dormant volcano is one that has erupted in the last 2000 years and may possibly erupt again. These can be dangerous as they are difficult to predict. The one on the Caribbean island of Montserrat last erupted 500 years ago but has made up for this with its massive eruptions in the last few years! • An extinct volcano has long since finished erupting and has cooled down. The UK’s volcanoes last erupted over 50 million years ago.

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tle s gen

8.2 The main features of earthquakes

wide base

magma chamber

Figure 8.3 a shield volcano

An earthquake is the result of a sudden release of energy that causes the Earth’s crust to shake, sometimes violently. Each day, there are at least 8000 earthquakes on the Earth. In a typical year, about 49 000 earthquakes are actually strong enough to be felt and noticed by

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tian

u Ale

Eurasian plate

ch ren

Juan Ring of fire de fuca plate

Filipino plate Hawaiian hot spot

Pacific plate

Arabian plate

Cocos plate

Nazca plate

South American plate

African plate

Australian plate

Mid-Atlantic ridge Caribbean plate

Eurasian plate

8 Earthquakes and volcanoes

North American plate

Scotia plate

Antarctic plate

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people and an average of 18 of these can cause serious damage to buildings and possibly injure and kill people.

Most of the world’s earthquakes (90% of them and 81% of the largest) take place along the Paciﬁc Ring of Fire – a 40 000 km long, horseshoe-shaped zone found along the edge of the Pacific Ocean (Figure 8.5). As plates move, the rocks on their edges may become locked together until, at the weakest point along a plate boundary – a fault line – they tear apart, or rupture, and this releases the strain. Earthquakes can also be produced by the movement of magma inside volcanoes. These earthquakes can serve as an early warning of volcanic eruptions. Some human activities can also trigger earthquakes, such as underground nuclear explosions and the creation of large reservoirs behind dams, the weight of which compresses and depresses the crust below them.

An earthquake’s point of initial tearing, or rupture, inside the Earth’s crust is called its focus (Figure 8.6). Earthquakes with a deep focus are found in the subduction zones beneath destructive plate boundaries. Those with a shallow focus are found along conservative and constructive plate boundaries. Shallow earthquakes can sometimes be very violent, as in Haiti in 2010, as their energy is not absorbed by the relatively thin crust above them and appears on the surface very quickly.

TERMS

Figure 8.5 active volcanoes, plate boundaries and the Paciﬁc ring of Fire

earthquake: a sudden and often violent shift in the rocks forming the Earth’s crust, which is felt at the surface fault line: a fracture or break in the Earth’s surface along which rocks have moved alongside each other focus: the location of the actual source of an earthquake below the ground surface; also called the origin conservative plate boundary: where two plates are sliding alongside each other epicentre: the location on the surface of the Earth above the focus or origin of the earthquake

The epicentre (Figure 8.6) is the point on the Earth’s surface directly above the focus, where the energy bursts onto the surface and spreads out in a series of shock waves. Earthquakes cause two major effects on the Earth’s surface – shaking and slipping of the crust. Surface movement by slipping in the largest earthquakes can be more than 10 metres. A slip that occurs underwater can create a huge wave called a tsunami (see Section 8.4). 71

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earth surface

fault line

Theme 2: The natural environment

epicentre of earthquake

focus of earthquake

movement along fault line under the Earth’s surface

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Earthquakes are recorded with a seismometer or seismograph, with the results displayed on a seismogram. Records of the seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of earthquakes.

TERMS

Figure 8.6 The features of an earthquake

There are two common scales used to measure the size of an earthquake:

1 The size of an earthquake is reported by the moment magnitude scale and quantifies the magnitude (the amount of energy) released by an earthquake. This scale was developed to replace the richter scale. Both are logarithmic scales, so that an earthquake of 7.0 releases about 32 times as much energy as one of 6.0 and 1000 times that of 5.0.

2 The moment magnitude and Richter scales only give a rough idea of the actual impact of an earthquake. An earthquake’s destructive power varies depending on the composition of the ground in an area and the design and placement of human-made structures. The Mercalli scale is rated on the extent of the physical damage caused by an earthquake. Mercalli ratings are given as Roman numerals and they are based on largely subjective interpretations of the physical damage caused by an earthquake.

tsunami: powerful, devastating waves at the coast caused by an undersea earthquake or volcanic eruption that displaces the water lying above it seismometer: an instrument that measures movement of the ground, including the seismic waves generated by earthquakes and volcanic eruptions seismic waves: waves of energy that travel through the Earth’s layers as a result of earthquakes, volcanic eruptions, magma movements and large landslides moment magnitude scale and richter scale: numerical scales showing the size or magnitude of an earthquake based on readings from a seismometer Mercalli scale: a scale showing the effect of an earthquake on the Earth’s surface aftershock: a smaller earthquake following after the main earthquake

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The layers of the Earth Integral to understanding the global pattern of plates and their movements is a knowledge of the structure of the Earth. The Earth, when seen in cross section, has four main layers (Figure 8.7)

plate (huge slabs of the crust)

crust

The Earth’s crust is split into many huge pieces called tectonic plates (see Figure 8.5). These pieces of crust float and move on top of the much denser mantle below them. The movement of these crustal plates is due to huge convection currents in the mantle below the crust. These convection currents move heat from the interior core of the Earth towards the surface. This movement of heat causes the mantle and, in turn, the crustal plates on top of the mantle to slowly move. The movement of the plates produces several distinct landforms, as well as causing earthquakes.

mantle

outer core

TERMS

plate boundary

Plate tectonics is the study and explanation of the global distribution of tectonic plates, fold mountains, earthquakes and volcanoes.

8.3 Distribution of earthquakes and volcanoes

If oceanic and continental crusts collide, the oceanic crust, being denser, will go under the continental crust, a process called subduction. Relative to the other layers, the crust is actually quite thin.

inner core

Figure 8.7 The structure of the Earth

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1 At the centre is the inner core, which is about 1400 km across. Here, the rocks are solid and extremely dense – they are about five times denser than the rocks at the surface.They are made out of iron (about 80%) and nickel and are extremely hot, about 5500 °C.

2 On the edge of the inner core is the outer core, which is made up of dense, semi-molten metal with a temperature of 5000–5500 °C. It is about 2100 km thick. 3 Outside the core is the mantle. This is also semimolten, but is less dense and makes up a layer which is about 2900 km thick. 4 At the surface is the crust. It varies in thickness and there are two types – oceanic crust and continental crust (Table 8.1). Oceanic crust Relatively thin – 5 to 10 km thick Younger Heavier/denser Continually being formed and destroyed

8 Earthquakes and volcanoes

After a major earthquake, it is common for there to be aftershocks. An aftershock is an earthquake that occurs after a previous earthquake. Aftershocks are formed as the Earth’s crust around a fault adjusts to the effects of the main shock.

Continental crust Relatively thick – 25 to 90 km thick Older Lighter/less dense Cannot be destroyed

Table 8.1 The differences between oceanic and continental crust

fold mountains: a long, high mountain range formed by uplifting and folding of sediments convection currents: differences in temperature of material beneath the plates of the Earth’s crust leads to the creation of currents to transfer the heat. These currents move the plates above them

Types of plate boundary Where two plates meet is called a plate boundary or plate margin. There are four types of plate boundary.

Constructive (divergent) plate boundaries This is where two plates move away from each other (Figure 8.8). Any gap that appears between these plates fills with molten magma and the lava that comes out forms/constructs new crust. One of the biggest and longest constructive margins is the Mid-Atlantic Ridge, which stretches down the middle of the North and South Atlantic oceans where the North and South American plates are moving away from the Eurasian and African plates. There are many undersea volcanoes along the ridge and minor earthquakes occur along it as the plates move. Both volcanic activity and earthquakes on these margins tends to be relatively gentle in comparison to the other margins.

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volcanic islands such as Iceland and the Azores

north American plate

Eurasian plate

sea level volcanoes

crust

Theme 2: The natural environment

mid-Atlantic Ridge

mantle

Figure 8.8 a constructive (divergent) plate boundary

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Where this process takes place in an ocean, the volcanoes may form a line of volcanic islands called island arcs, as in the islands of the West Indies in the Caribbean and in the Aleutian Islands, south west of Alaska. Destructive margins often suffer from very powerful earthquakes, such as the Chile earthquake of 1960, which was the largest ever recorded at 9.5 on the Richter scale, and the Japanese earthquake of March 2011, which was 8.9 and the fifth largest ever recorded.

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These are found where plates made of heavier oceanic crust move towards plates made of lighter continental crust (Figure 8.9). Where they meet, the heavier oceanic crust is forced down under the lighter continental crust and forms a subduction zone. As the oceanic crust sinks deeper, it melts and forms magma. This may rise to the surface and emerge as lava. It forms very explosive volcanoes, as in the Andes Mountains in South America, where the Nazca Plate is moving under the South American Plate.

TERMS

Destructive (convergent) plate boundaries

If you are asked about the formation of volcanoes in island arcs, as well as mentioning the presence of plate boundaries, also explain that the subduction zone extends beneath these volcanoes and refer to the processes of subduction and melting taking place.

subduction zone: the zone where one tectonic plate sinks (subducts) under another island arc: a chain of volcanic islands located above a subduction zone at a tectonic plate boundary

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fold n ntai mou

sea level

lighter continental plate/crust

lava

heavier oceanic plate/crust

volcanic eruption

ocean

8 Earthquakes and volcanoes

deep sea trench

mantle

earthquake focus as plates slide past each other

melting due to a combination of heat generated by friction and heat from the mantle

melting oceanic crust

Figure 8.9 a destructive (convergent) plate boundary

Conservative plate boundaries

earthquakes, such as in Haiti in January 2010, but they do not produce volcanic eruptions and land is not created or destroyed. The San Andreas Fault in California is another famous example.

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These occur where plates slide past each other (FigureÂ 8.10). Sometimes they become locked together and pressure builds up until they tear apart, along a fault line. These movements can produce very powerful

earthquake epicentres

oceanic plate

fau

continental plate

lt l

ine

earthquake focus

Figure 8.10 a conservative plate boundary

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lighter continental crust

fau

lighter continental crust

lt l

ine

Theme 2: The natural environment

mountains e.g. Himalayas

mantle

Collision plate boundaries

Figure 8.11 a collision plate margin

impacts on people

This is where two continental plates converge/move towards each other (Figure 8.11). These lighter plates are not dense enough to sink into the mantle. As the plates collide, they fold up and form fold mountains, such as the Himalayas. These collisions can also produce powerful earthquakes, as witnessed in Nepal in 2015, but they do not produce volcanic eruptions.

• The loss of life from collapsing buildings, bridges and elevated roads, fire and disease. Children and other dependents can be orphaned or left without any family support. Survivors may face serious psychological and emotional problems for many years afterwards.

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Self-test questions 8.1

The impacts of earthquakes and volcanoes will vary according to a combination of factors at any particular place, but earthquakes and volcanic eruptions both have a similar range of hazardous results:

Describe the global distribution of volcanoes and earthquakes.

Explain how their distribution is related to movements at plate boundaries.

8.4 Effects of earthquakes and volcanoes on people and the environment

The effects of earthquakes and volcanos are often classified as being either primary or secondary. Primary effects occur as a direct result of the earthquake or volcanic eruption, such as buildings collapsing due to the ground shaking or loss of life due to pyroclastic flows. Secondary effects occur as a result of the primary effects, such as the impact of tsunamis, fires caused by ruptured gas mains or higher insurance premiums.

• The cutting of basic necessities such as power, water, sewage treatment due to damage to power lines, water and sewage pipes. • The collapse of buildings or the destabilisation of the base of buildings which may lead to collapse in aftershocks and future earthquakes and general damage to houses and buildings. People may be homeless for weeks, months or years. • Road, railway and bridge damage which can make access difficult or impossible to earthquakeaffected areas. • The loss of crops as they are covered in ash, loss of trees in the areas near the volcano. • Fish can be killed in rivers, lakes and hatcheries by ash getting into streams and rivers. • The spread of disease due to polluted water and lack of medicine when water and sewage pipes are broken and water becomes polluted with sewage.

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– In older residential areas, where buildings were not made resilient to earthquake movements – as in the Kyoto earthquake in 1995 – this can cause large loss of life and injuries.

• Higher insurance premiums for those people in earthquake-affected areas where insurance companies are not prepared to take the potential risk.

Earthquakes

• contamination – after earthquakes, water supplies may become contaminated as they mix with sewage, and hunger may be a problem where food and water cannot reach affected communities; in winter, people without shelter and winter clothing may suffer from hypothermia.

The amount of damage caused by earthquakes will depend on a combination of factors:

• secondary hazards – these can include tsunamis on the coast, landslides and rock falls in mountainous areas, fires in urban areas – many caused by broken gas pipes and electricity lines

Most people agree that human loss of life is the most significant impact of earthquakes and volcanic eruptions. LICs and many MICs, such as Haiti, Afghanistan and Pakistan, do not have the resources to adequately deal with such disasters compared to HICs, such as the USA, Japan and Italy.

– During working hours, people in cities and towns will be working in office blocks or inside school. Such buildings will normally be earthquake proof.

8 Earthquakes and volcanoes

• The loss of jobs and businesses when factories, offices and places of work are destroyed.

• depth of the earthquake – many earthquakes take place deep in the crust, below 150 km, so much of their energy is absorbed by the crust above them

As seen earlier in this section, volcanoes produce a wide variety of hazards that can injure and kill people, and destroy property. However, unlike earthquakes, large, explosive eruptions can endanger people and property hundreds of kilometres away and even affect global climate. An explosive volcanic eruption can blast solid and molten rock fragments (called tephra) and volcanic gases into the air with tremendous force. The largest rock fragments (volcanic bombs) usually fall back to the ground within 2–3 km of the vent. Small fragments (less than about 1 mm across) of ash rise high into the air, forming a huge, billowing eruption column. These can grow rapidly and reach more than 20 km above a volcano in less than 30 minutes, forming an eruption cloud. The volcanic ash in the cloud can pose a serious hazard to planes. During the past 15 years, about 80 commercial jets have been damaged by inadvertently flying into ash clouds, and several have nearly crashed because of engine failure.

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• distance from the epicentre – as the shock waves spread away from the epicentre, they become weaker

volcanoes

• geology of the rocks in the area – loose sedimentary rocks may liquefy and cause buildings and structures to sink into the ground; more solid, harder rocks will normally provide the safest foundations for buildings

• building construction materials and designs – steel-framed buildings are better able to absorb movement than concrete-framed buildings

• space between buildings – as buildings sway, they may hit each other if they are built too close to each other and become damaged • number of storeys – in a tall, high-rise building, shock waves become amplified as they move up the building, which can cause them to sway and collapse • density of population – a densely populated urban area is likely to suffer many more casualties and damage than a low-density rural area

TERMS

• strength of the initial earthquake and the aftershocks that may follow it – the Haiti earthquake in January 2010 measured 7.0 on the Richter scale which was powerful enough to destroy buildings

tephra: rock fragments and particles ejected by a volcanic eruption fumarole: an opening in or near a volcano, through which gases, such as sulphur dioxide, are emitted

• time of the day when the earthquake occurs – at night in residential areas most people will be inside their homes and asleep

• Volcanoes provide raw materials such as sulphur, zinc, gold and diamonds which can be mined and sold. • Volcanoes can attract tourists and local people can get jobs as tour guides. The people who live in towns near Mount Etna in Italy such as Messina and Catania, can earn money from renting accommodation to tourists.

Volcanoes can emit large volumes of gases during eruptions. Even when a volcano is not erupting, cracks in the ground allow gases to reach the surface through small openings called fumaroles. More than 90% of all gas emitted by volcanoes is water vapour (steam), most of which is heated ground water (underground water from rainfall and streams). Carbon dioxide is heavier than air and can be trapped in low-lying areas in concentrations that are deadly to both people and animals. Fluorine gas, which in high concentrations is toxic, can be adsorbed onto volcanic ash particles that later fall to the ground. The fluorine on the particles can poison livestock grazing on ash-coated grass and also contaminate domestic water supplies.

• People can obtain hot water for heating and also generate electricity from the volcano using the hot steam to produce geothermal power.

• Governments, as in Italy, can set up volcanic and earthquake prediction equipment and then local people may feel more secure in living in highrisk areas.

Theme 2: The natural environment

Large eruption clouds can extend hundreds of kilometres downwind, resulting in ash fall over enormous areas. Heavy ash falls can collapse buildings, and even minor ash fall can damage crops, electronics and machinery.

Lava flows can spread out in broad sheets several kilometres wide. Deaths caused directly by lava flows are uncommon because most move slowly enough that people can move out the way easily. Lava flows, however, can bury homes and agricultural land under tens of metres of hardened rock.

8.5 Reducing the impacts of earthquakes and volcanoes Responses to earthquakes and volcanic eruptions are both short term, such as emergency aid and disaster relief, and long term, such as risk assessment, rebuilding, improving hazard prediction and preparation for future hazards.

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High-speed avalanches of hot ash, rock fragments and gas can move down the sides of a volcano during explosive eruptions or when the steep side of a growing lava dome collapses and breaks apart. These pyroclastic flows (see Section 8.1) tend to follow the direction of valleys on the side of a volcano and are capable of knocking down and burning everything in their paths. Lahars (flows of mud, rock and water) can rush down valleys on the sides of volcanoes at speeds of 30–100 km per hour and can travel more than 300 km, covering large areas of land. Some lahars contain so much rock debris (60–90% by weight) that they look like fast-moving rivers of wet concrete. These flows are powerful enough to rip up and carry trees, houses and huge boulders miles downstream.

• Many people have lived near volcanoes and earthquake zones all their lives. They are close to their family and friends, they work in the area and many cannot afford to move away.

Volcanoes can offer opportunities for people

Despite the hazards, many people live in areas where they are likely to encounter volcanic eruptions. They do this for a number of reasons.

• Volcanic soils are often very fertile and yields of crops are high: in the case of Mount Etna in Italy, the fertile volcanic soils support extensive agriculture with vineyards and orchards spread across the lower slopes of the mountain and the broad Plain of Catania to the south.

There are several things that can be done to help people live more safely in earthquake and active volcanic zones: • Improved technology and use of historical data can improve the prediction and forecasting of earthquakes and volcanoes to provide warnings. • Mapping of high-risk areas where buildings are at risk from liquefaction, mudslides, landslips, lahars, lava flows and pyroclastic flows can ensure that such areas are not used for building. • Improved building designs and materials can mean that buildings do not collapse during earthquakes. Buildings with deep foundations made of special rubber can absorb shock waves more easily. Steel-framed buildings, with steel cross braces can move more than rigid, concrete buildings and stay intact. Automatic shutters that close on windows can stop glass falling on people below the buildings. Shatter-proof glass can also be used in windows.

• Gas sensors monitor the release of gases from the volcano. • Satellites can monitor changes in the shape of a volcano and increases in temperature. Once lava has erupted, it may be possible to halt or divert lava flows by building concrete dams or spraying water on their fronts to solidify the lava and help dam and divert it.

Predicting volcanic eruptions There are a number of ways scientists help predict and then prepare people for volcanic eruptions:

Self-test questions 8.2

1 Explain why earthquakes of the same strength may cause different numbers of deaths.

• Seismometers record the increasing number of earthquakes that are caused by huge amounts of magma pushing up under a volcano.

• Ensuring that adequate emergency drills and procedures are in place, both at home and for people at work and in schools and hospitals. The stockpiling of emergency supplies of medicines, drinking water, tinned food, tents and blankets can mean that there can be a rapid response to any earthquake or volcanic eruption.

• Thermometers measure increases in temperature.

8 Earthquakes and volcanoes

Flexible pipes can be used for water and gas, as well as systems that shut off water and gas flows automatically when an earthquake occurs.

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• Tilt metres measure the changes in the volcanoes’ shape as they start to bulge with the upward movement of magma.

2 Explain why many volcanic areas are popular places to live but can create problems for the people living in those areas.

Case studies An earthquake – Sichuan province, China, May 2008 There are several ways to protect people in locations such as Sichuan from future earthquakes:

• build houses and schools which are more stable and designed to sway not collapse • make sure that planning regulations are followed • build deeper foundations on buildings • use flexible water and gas pipes

• make sure there is an automatic gas switch-off when an earthquake occurs

The Great Sichuan earthquake in China in May 2008 measured 7.9 on the Richter scale. The earthquake was caused by the movement of a large fault line between the Eurasian and Indo-Australian plates. The movement took place along a 240 km section of the fault down to a depth of 20kms. In two minutes the land moved 9 metres along this fault causing extensive damage and loss of life on the surface. It occurred in the midafternoon when children were at school and people were at work. Over 7000 schoolrooms collapsed, mostly in rural areas, leading to the death of over 5000 students and the injury of around 15 000 more. The large number of school collapses was because many were not built to agreed adequate standards through corruption and mismanagement. Many other buildings collapsed, as they were poorly constructed and were not earthquake proof. The earthquake affected a wide area which contained large settlements and the region was densely populated. There were many gas leaks and fires as gas pipelines were ruptured by the movement. Roads were blocked and badly damaged which delayed emergency services. The rupturing of sewage and freshwater pipes meant that there was contamination of water and a lack of drinking water. In total, the earthquake killed almost 69 200 people and left over 18 200 missing.

• have frequent earthquake drills and make sure there is education of safety procedures and that people and the government stockpile supplies of drinking water, food, clothing/blankets and tents, etc • build on solid ground

• ensure the emergency services are better prepared

• restrict building heights and improve their design.

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Reasons why people live in high-risk areas such as Sichuan

There were many long-term effects which resulted from this earthquake: • damage to workplaces, so that people were unable to earn a living • a negative impact on the economy and industrial production

• damage to infrastructure – roads, railways, power lines, water, gas and sewage pipelines

• the economic cost of rebuilding the infrastructure and housing

• damage to schools and the disruption of education

• the psychological trauma of experiencing an earthquake and the loss of family and friends

There are many reasons why so many people live in areas such as Sichuan, even though they are at risk from earthquakes: • They have lived there all their lives, are close to their friends and family, and have a sentimental attachment to the area. • There is lots of work in the area and it has fertile farmland. This means that they can make a good living. • There are good services/schools/hospitals in the area.

• There is pressure on living space in an area that is very mountainous. • They are confident about their safety and are willing to take the risk as an earthquake has not occurred for many years.

• homelessness.

phreatic eruption: an eruption caused by groundwater in the sides of the volcano being turned into large volumes of steam and erupting along with large amounts of ash and volcanic bombs

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Mount Ontake is a massive strato-volcano and the second highest in Japan. Although the volcano is under constant surveillance for changes in its shape – tilt metres on its sides, seismometers and a camera monitoring its state – an eruption in 2014 killed 57 people, highlighting the problems faced in predicting volcanic eruptions, even in HICs. There were no significant earthquakes that might have warned authorities in the lead up to this phreatic eruption. When it erupted, over 300 walkers and climbers were on the volcano and had little chance of escaping the effects of the volcanic bombs, ash and hydrogen sulphide gas.

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The government has set up anti-disaster councils formed from the police, firefighters and volcano experts, who have created hazard maps showing the extent of expected damage, based on a multiple scenario of eruptions and they have devised evacuation plans for both residents and tourists.

The short-term impact was the effect of the eruption and its volcanic bombs, ash and gas on the 300 walkers and climbers. The short-term response included the very quick deployment of hundreds of trained and equipped emergency responders, including helicopters. The long-term response was a recognition that this was already a monitored volcano but the instruments on the volcano had not recorded any measurable ground deformation or any seismic activity. The long-term impact was therefore to look at ways of improving the monitoring of the volcano by looking at ways in which small-scale phreatic eruptions like this can be monitored as this eruption was neither expected nor its impacts prevented.

Japan has 110 active volcanoes, 50 of which have roundthe-clock monitoring. Japan has about 10% of all the active volcanoes in the world. Its volcanoes form part of the Pacific Ring of Fire. The eruption of Mount Ontake was caused by the subduction of the oceanic Philippine plate beneath the continental Eurasian plate. The melted magma from the subducting oceanic Philippine plate rises through the continental crust and produces spectacularly violent eruptions.

Case studies

a volcano – Mount ontake, Japan, 2014

Suggest different ways to protect people from earthquakes. [4]

Explain why many people continue to live in areas where they are at risk from earthquakes. [5]

Explain the causes of an earthquake which has occurred in a named area that you have studied. [6]

In the first two parts of the question, you should list ways to protect people and reasons why people still live in earthquake zones. In the third part, use a detailed case study of an area affected by an earthquake with an explanation of the plate boundary that has caused the earthquake.

There are many different ways to protect people from earthquakes. Firstly, their houses can be built to resist the effects of being shaken by the earthquake [1] so that they do not collapse. A steel frame can be used which moves and bends, rather than collapses unlike a concrete building [1]. They can also be built on deeper foundations [1]. People should make sure that they follow building rules and regulations [1] and authorities do not allow people to build with the wrong materials and that they are built on solid ground [1]. Authorities should make sure that people are aware of what to do when an earthquake hits

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Many people have lived for generations in earthquake areas so they are surrounded by their friends and family [1] and they have built their homes and developed their farms in that area [1]. Many people are just not rich enough to be able to move away and set up a new farm or buy a new house [1] and they may not get much money for their land or be able to sell their house because it is in a dangerous area [1] or find new employment to support themselves and their families [1]. When they balance the advantages and disadvantages of moving, they may decide to stay and take the risk [1], especially if an earthquake has not happened for many years and they feel safe because of that [1]. (A maximum of 5 marks will be awarded.)

and that they have emergency supplies ready of water and medicines [1]. (A maximum of 4 marks will be awarded.)

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Theme 2: The natural environment

Sample question and answer

California is in an earthquake zone and has had lots of earthquakes. Many of them are along the San Andreas Fault line which is a line of weakness between two plates called the North American and Pacific plates [1]. These plates are sliding past each other along this fault line [1] along what is called a conservative boundary [1]. Sometimes the two plates get stuck and pressure builds up [1] until they suddenly slip a few metres [1]. This big movement sends out shock waves which can destroy buildings and it has done this in both Los Angeles and San Francisco [1]. (A maximum of 15 marks will be awarded).

Exam-style questions 1

What are volcanoes?

[2]

Explain why some volcanoes are different in size and shape from each other.

Why do mudflows occur during volcanic eruptions and what problems do they cause? [2]

[4]

In what ways do earthquakes cause damage to people and the environment? [4]

Cambridge IGCSE® Geography Revision Guide Second edition David Davies

Sample answers to all the questions are in the back of the book.

From tourism in Kenya to the summit of an active volcano in Japan, this revision guide helps students understand the processes that affect physical and human environments on a local, regional and global scale. Exam-style questions, international case studies and example maps, give students practice with course content in preparation for assessment. This revision guide is for the Cambridge IGCSE Geography syllabus (0460), for examination from 2017.

Features: • Detailed descriptions help students to revise thoroughly • Self-test questions alongside topics provide students with useful activities that reinforce core concepts • Exam-style questions and sample answers help students develop their skills in preparation for assessment • The full-colour design supports development of map reading skills and aids navigation

9781107458949 9781316503614

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Other components in the series: Coursebook with CD-ROM Teacher’s Resource CD-ROM

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IGCSE Geography syllabus for examination from 2017

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