Author:
Alex Woolf studied history at Essex University, England. He is the author of over 60 books for children, including The Science of Rocks and Minerals: The Hard Truth About the Stuff Beneath Our Feet, You Wouldn’t Want to Live Without Poop!, and You Wouldn’t Want to Live Without Vegetables! Artists:
Andy Rowland Bryan Beach Editor:
Jacqueline Ford
© The Salariya Book Company Ltd MMXVIII No part of this publication may be reproduced in whole or in part, or stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission of the publisher. For information regarding permission, write to the copyright holder. Published in Great Britain in 2018 by The Salariya Book Company Ltd 25 Marlborough Place, Brighton BN1 1UB ISBN-13: 978-0-531-22766-4 (lib. bdg.) 978-0-531-23076-3 (pbk.)
All rights reserved. Published in 2018 in the United States by Franklin Watts An imprint of Scholastic Inc. A CIP catalog record for this book is available from the Library of Congress. Printed and bound in Heyuan, China. Printed on paper from sustainable sources. Reprinted in MMXIX. 2 3 4 5 6 7 8 9 10 R 26 25 24 23 22 21 20 19 SCHOLASTIC, FRANKLIN WATTS, and associated logos are trademarks and/or registered trademarks of Scholastic Inc., 557 Broadway, New York, NY 10012. This book is sold subject to the conditions that it shall not, by way of trade or otherwise, be lent, resold, hired out, or otherwise circulated without the publisher’s prior consent in any form or binding or cover other than that in which it is published and without similar condition being imposed on the subsequent purchaser.
The
Science of
Natural
Disasters
The Devastating Truth About Volcanoes, Earthquakes, and Tsunamis W r it t e n b y
f l o o W x e l A Franklin Watts® An Imprint of Scholastic Inc.
I llu st ra te d by
A n d y R o w la n d
Contents Introduction 5 Cracks in the Crust
6
How Volcanoes Form
8
Fountains and Explosions
10
The Impact of Eruptions
12
How Earthquakes Happen
14
Caught in a Quake
16
After the Quake
18
How Tsunamis Happen
20
When Tsunamis Strike
22
After the Waves
24
Rebuilding 26 Predicting Disasters
28
Glossary 30 Index 32
Introduction
E
arth provides for all our needs. It gives us air to breathe, food to eat, and fresh water to drink. But our planet can also be violent and destructive. Volcanoes erupt, sending out clouds of ash and rivers of molten lava. Earthquakes shake up the land, destroying buildings and sparking destructive fires. Tsunamis— enormous ocean waves—crash onto the shore, devastating coastal communities. In this book we’ll look at how and where volcanoes, earthquakes, and tsunamis happen, and their powerful impact on people and the environment. And we’ll investigate how, with better scientific understanding of these disasters, we may be able to reduce tragic losses of life in the future.
7
Currents within the mantle set the tectonic plates drifting across the globe. They move very slowly, at around 1 to 6 inches (2.5 to 15 centimeters) per year, but they never stop.
Convergent Faults rgent fault, tectonic
At a conve plates push into each other. As a result of these collisions, earthquakes and volcanoes are common in these areas. In some cases, mountain ranges form.
Cracks in the Crust
T
he hard, rocky surface of Earth is called the crust. Beneath the crust is the mantle, a layer of partially molten rock thousands of miles deep. The crust isn’t one solid layer. It is broken up into about thirty sections called tectonic plates. These plates fit together like a giant jigsaw puzzle to cover the whole surface of Earth. The boundaries where the tectonic plates meet are called faults. It is along these faults that most earthquakes and volcanic eruptions happen. When an earthquake or volcanic eruption occurs under or near the ocean, it can trigger a tsunami. There are three kinds of faults: convergent, divergent, and transform.
The mountain’s rising faster than you are.
8
Fault lines
lts Transform Faults Divergent Fau At transform faults, plates es at At divergent faults, pl lcanic move apart, causing vo ten activity as magma (mol rises rock) from the mantle ma to fill the gap. The mag This cools to form new land. ht process is happening rig tic now, beneath the Atlan Atlantic Ocean. As a result, the es ch is growing by a few in each year.
grind against each other as they move in opposite directions. Transform faults can lead to earthquakes. Most, but not all, are on the ocean
floor. There is one in California called the San Andreas Fault, where one plate is moving south and the other north. As a result, California has regular earthquakes.
It was San Andreas’s Fault.
I’m sure it takes longer to cross the Atlantic each time!
Around 250 million years ago, Earth had just one vast landmass called Pangaea. Gradually, over millions of years, the movement of the tectonic plates caused Pangaea to break up, creating the world as it is today.
Fascinating Fact
Iceland is on the Mid-Atlantic Ridge, the divergent fault in the middle of the Atlantic Ocean. As a result, there are cracks in the landscape where rock has been torn apart. Iceland also experiences a lot of volcanic activity, leading to the formation of new rock and new islands.
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There’s a major belt of volcanoes around the edge of the Pacific Ocean, known as the Ring of Fire.
Hot Spots
Some volcanoes form in the middle of tectonic plates, far from the boundaries, in hot spots. These are places where the hot mantle melts, forces its way through the crust, and erupts as lava. Hot-spot volcanoes in the oceans form underwater mountains called seamounts. The Hawaiian Islands are the summits of giant seamounts.
m r o F s e o n a lc o V w o H
V
olcanoes form in places where magma forces its way out of a crack in Earth’s crust. This can happen at divergent faults, where two tectonic plates move apart, allowing magma to rise to the surface. Most of these volcanoes are located on the seafloor. Volcanoes can also occur at convergent faults, where two plates collide. One plate slides under the other and moves down into the mantle. This is called subduction, and the area where it happens is the subduction zone. The lower plate partially melts in the mantle, making new magma that rises up to form volcanoes.
Rising magma Continental crust
Oceanic crust Oahu
Maui
Hawaii Hot spot
10
Su
bd
uc
tio
nz
on
e
Melting magma
Parts of a Volcano Many volcanoes are shaped like cones. The cone is made up of layers of solidified lava and ash from past eruptions. Beneath the volcano is a
magma chamber. Magma rises through a central tube called a vent, erupting from the crater at the top. Magma may also erupt from side vents.
Active, Dormant, and Extinct I can’t tell if he’s dormant or extinct.
Crater Side vent
Vent
Layers of lava and ash
Lava flow
Magma chamber
Lava varies depending on the kind of rock it’s formed from. Some types flow easily like syrup; other types are thick and sticky like tar.
Active volcanoes are volcanoes that have erupted in the past 10,000 years. Dormant volcanoes are volcanoes that have not erupted in the past 10,000 years, but experts think they are still capable of erupting. Extinct volcanoes are volcanoes that nobody expects will erupt again.
Fascinating Fact The word volcano comes from Vulcan, the Roman god of fire. According to legend, Vulcan lived on the island of Vulcano off the southwest coast of Italy. He worked as a blacksmith making weapons for the other gods. The Romans believed the eruptions from the island’s volcano were sparks from Vulcan’s forge.
11
s n o i s lo p x E d n a Fountains Stratovolcanoes The magma at convergent faults, where stratovolcanoes form, can be thick and sticky. It blocks the volcano’s vent until the pressure from the magma chamber becomes too great, and the volcano erupts in a huge explosion.
In 1991, Mount Pinatubo, a stratovolcano in the Philippines, erupted. The collapse of the top of the volcano caused by the eruption took 984 feet (300 meters) off the top of the mountain.
12
V
olcanic eruptions are not all the same. Some are gentle while others can be explosive. Each type of eruption builds different kinds of volcanoes. Gentle eruptions, which happen at divergent faults and hot spots, build shield volcanoes. These are wide and low with sloping sides, like an upside-down plate. Shield volcanoes erupt frequently. Explosive eruptions, which happen at convergent faults, build steep-sided, cone-shaped volcanoes called stratovolcanoes. These volcanoes erupt only rarely, and the eruptions are usually violent and dangerous. Go ahead! Show us what you can do! Don’t tempt me!
Kilauea, a shield volcano in Hawaii, is the most active volcano on Earth. Erupting almost constantly since 1983, it produces lava fountains that shoot up to half a mile (0.8 km) into the air.
Pyroclastic Flows
When eruption columns get too heavy, they collapse and sweep down the volcano’s side in a pyroclastic flow. These red-hot avalanches can travel up to 100 miles (160 km) per hour,
destroying everything in their path. In 79 CE, a pyroclastic flow from Mount Vesuvius engulfed the Roman town of Pompeii. The town was preserved under the ash and pumice.
Shield Volcanoes
Shield volcanoes produce lava that is fluid and runny. Gas in the lava makes it shoot upward like a fountain. After falling back to Earth, the lava flows down the volcano in glowing red rivers called lava flows. Two types of lava are produced: pahoehoe and aa. When it cools, pahoehoe has a smooth, ropy surface, while aa has a rough, lumpy surface.
No, pahoehoe. Aaaah!
Baking soda
Try It Yourself Place a small empty jar in a mound of dirt. Add two spoonfuls of baking soda, a spoonful of dish soap, and a few drops of red food coloring. Now for the eruption! Add 1 fluid ounce (30 milliliters) of vinegar. The vinegar and baking soda will react, causing a beautiful spout of “lava”!
Jar
Dish soap
Food coloring
Vinegar
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