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Scott Foresman Science 4.9

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Glossary

Earths Surface

ISBN 0-328-13884-3

1. What is physical weathering? Give two examples of it.

2. How can the effects of erosion be limited?

3. What can trigger an avalanche?

4. Volcanoes can cause extensive damage. Write to explain why volcanoes are so destructive. Include details from the book to support your answer.

5. Compare and Contrast What are some similarities between earthquakes and volcanoes? What are some differences?

What did you learn?Vocabularydepositionearthquakeepicentererosionfaultlandformslandslidevolcanoweathering

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: Getty Images; 1 Getty Images; 2 (BL) Getty Images; 3 (BR) Getty Images, (CR) Comstock Inc.;4 (BL) Getty Images, (CR) Digital Stock; 5 Getty Images; 6 Getty Images;7 (BR, CR) Getty Images, (T) Yann Arthus-Bertrand/Corbis; 8 (T) /Corbis, (BL) Getty Images; 9 Getty Images;10 (BL) Getty Images, (R) Galen Rowell/Corbis; 11 (BR) Getty Images, (BL) Niall Benvie /Nature Picture Library;12 (BL) Getty Images, (C) Digital Stock; 13 (BR) Getty Images, (BC) Bembaron Jeremy/Corbis Sygma;14 (BL) Getty Images; 15 (BR) Getty Images, (BC) Roger Ressmeyer/Corbis; 16 Getty Images.

Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson.

ISBN: 0-328-13884-3

Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,mechanical, photocopying, recording, or likewise. For information regarding permission(s), write toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

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by Lorrie Oestreicher

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How Earths Surface Changes

The surface of Earth is constantly being worn away by many forces. This can happen very slowly or over a long period of time.

Earths CrustThe part of Earth we see is actually a very thin layer

of rock called the crust. You cant see Earths crust in the ocean because it is deep below the surface.

Earths natural features are called landforms. A canyon is one shape that Earths crust can take. Other landforms include hills, islands, and peninsulas. Streams, plateaus, and glaciers are also landforms. Can you think of more?

glacier

island

High areas, low areas, fl at areas, rugged areasthey all vary in size, shape, and age. How were they formed? How do these landforms change?


WeatheringThe surface of Earth is always

changing. Weathering causes rocks to break down slowly into smaller pieces. There are many causes of weathering. Some causes are the movement of water, changes in temperature, and the actions of living things. Rocks may weather physically or chemically.

canyon

Landforms can develop quickly, or they can take millions of years to appear. A volcano can change the shape of land very quickly when it erupts. But it takes a long period of time for a hill to form. Have you ever seen the Grand Canyon? Think about how long it took for a landform of that size to form!

stream

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Physical WeatheringPhysical weathering changes only the size of the

rocks. As the water in rivers and streams moves, it carries pieces of rock with it. These pieces tumble against each other and slowly become smaller and smaller.

Rainwater or melting snow can soak into the cracks in rocks. This water freezes into ice. Ice takes up more space than liquid water. It causes the cracks in rocks to grow deeper. Over time the pressure of the ice can cause

rocks to break apart.Plant and tree roots

put the same kind of pressure on rocks when they grow in cracks. As roots grow, they force the cracks to become wider and deeper. Eventually the rock splits apart.

When the Sun heats a rock, the

rock expands, or gets bigger. As the rock cools, it contracts, or gets smaller. This continual heating and cooling can weaken the structure of the rock.


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Chemical WeatheringChemical weathering does more than break down

rocks into smaller pieces. When chemical weathering occurs, it also causes changes to the materials that make up the rock and soil.

Some rock minerals are changed into different minerals as they react with chemicals in the air and water. For example, a mineral such as pyrite forms a

Water fl owing long ago and continued erosion weather rock into formations such as those in Arches National Park in Utah.

weak acid when it dissolves in rainwater. This acid can eat away at rocks and weather them.

Rocks can experience weathering from chemicals that plants and animals release. Rocks can also be weathered by chemicals that come from things people do.


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How Weathered Materials Move

Erosion

Weathered pieces of rock can be moved to new places. These movements can contribute to the development of new landforms.

Erosion continues the work that weathering started. Erosion transports weathered rock material to a new place. Wind, water, ice, or gravity can cause erosion.

Raindrops can strike the ground with enough force to wash away loosened material from the surfaces of rocks. As rain continues, water fl ows across the ground. It picks up and carries away the loosened soil particles and deposits them in rivers. From there the particles may travel all the way to the sea.

The pull of gravity helps rainwater fl ow downhill. As time passes, streams are created in the tiny channels, or grooves, carved by rainwater. These channels deepen and widen, forming valleys and canyons.


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Waves pounding against the shore carry bits of sand away. The waves also beat against rocks on the shore. Pieces of those rocks slowly wear away. Waves move them to new places. While some beaches are being worn away, others may be forming.

Glaciers are huge masses of slowly moving ice that erode the land they move over. The ice at the bottom of the glacier melts, and the glacier moves along this layer of water. As it moves, it takes with it particles of rock and soil. Glaciers are strong enough to move large pieces of rock.


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DepositionWind and moving water become strong forces for

erosion when they carry sand and dust. What happens to all the moving soil, sand, pebbles, and rocks when fl owing water and wind slow down? Water current slows rapidly as it enters a lake or ocean. The largest, heaviest pebbles fall to the bottom. Then sand and other smaller particles sink. Finally the lightest materials, called silt, drop to the bottom. This buildup of soil and rock forms new areas called deltas, which are found at the mouths of rivers. This laying down of Earths materials and building up of new areas is called deposition.

aerial view of the Mississippi River delta


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No place on Earth is completely fl at. Gravity moves all objects from higher places to lower ones. Loosened rock and soil high on a hillside or in mountains can move downhill. This may happen slowly over a period of time, or it may happen very fast. If it happens quickly, the moving pieces can gather speed, picking up other loosened materials. This quick downhill

Landslides

Wind cannot carry as much material as fl owing water can. Wind is usually only capable of moving very small particles, such as sand. In a desert, wind can cause sand to form piles called sand dunes. The wind reshapes these dunes continually.

movement of many rocks and bits of soil is called a landslide. Anything in its path may be carried along with the sliding rock and soil. A landslide can even move houses and cars! Heavy rains may cause a landslide to start by soaking the ground and making it unstable.


AvalanchesAvalanches happen

when snow and ice start sliding quickly down a mountain. Avalanches may be triggered by earthquakes, explosions, or even very loud noises. Landslides and avalanches cause extensive damage to places below. But people have found ways to try to stop avalanches from happening. One way is to not let snow build up to dangerous depths. Landslides and avalanches gain power as they rush down the side of a mountain. The higher up on a mountain that a landslide or an avalanche starts, the more destructive it can be.

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The natural processes of weathering, erosion, and deposition depend on the forces of wind and water. We can limit the effects of erosion by practicing careful land management. Land areas without plants and trees have nothing to stop the wind and rain from eroding their rocks and soil.

Farmers have learned to use a method called terracing to help trap water when planting crops across hillsides. This prevents rainwater from moving quickly down a hill and taking rock and soil particles with it.

Shorelines can be protected by having barriers built out into the water. The barriers help reduce the force of

waves hitting the land. This protects the sand on the beach from being carried out to the ocean.

How to Control Erosion And Deposition

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How Earths Surface Changes Rapidly

Volcanoes

Volcanoes and earthquakes bring about very fast changes to Earths surface.

A volcano is a landform. Many things are happening deep in the ground beneath a volcano. Magma is very hot rock found far below the surface of Earth. It is partially melted into liquid. Gas within the magma pushes it upward. When the magma reaches the surface, a weak spot forms in Earths crust. This is called a volcano. A volcano erupts when the magma reaches the surface. Magma that escapes onto Earths surface is called lava.

Volcanoes erupt in many different ways. Sometimes they do little more than release gentle puffs of ash and gases. Other times they cause violent explosions that blast dust, ash, rocks, gases, and burning clouds miles into the atmosphere.

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Volcanoes can blast ash, dust, and gases high into the atmosphere. Mount Etna in Sicily is one of the most active volcanoes in the world. In 2000 Mount Etna experienced a violent eruption. It sent ashes fl ying two miles into the air. A nearby city was covered in volcanic dust. The eruption sent lava running down the sides of the volcano.

After an Eruption

Active volcanoes are those that are likely to erupt. The Mauna Loa volcano in Hawaii is an active volcano. It has erupted more than thirty times since its fi rst recorded eruption in 1843. Volcanoes that have not erupted for many years, but still could erupt, are called dormant volcanoes. Mount Hood in Oregon

had its last eruption in the early 1900s. Volcanoes that will never erupt again are

extinct volcanoes. Mount Kilimanjaro in Tanzania, Africa, is an extinct volcano.

Active and Dormant Volcanoes

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This entire street as well as the car are covered in volcanic dust.


EarthquakesEarths crust fl oats on top of another layer called the

mantle. The crust is not solid. It is broken into about seven large and many smaller slabs. The sections of crust and the pieces of mantle under them are called plates. The plates move often.

A fault is a crack or separation in Earths crust caused by the movement of plates. Rock may become stuck along a fault. The plates continue to move, which puts pressure on the rock. If there is enough pressure, the rock can break. At that point the plates will move suddenly. An earthquake is caused by this abrupt movement of Earths plates. It makes the crust shake. The focus is the place below the ground where the plates move and where the earthquake begins. The point on Earths surface that is directly above the focus is the epicenter.

The energy from an earthquake moves in waves. While these shock waves may be felt far away, they are strongest at the epicenter.

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fault line

focusepicenter

crust mantleshock wave

Earthquakes occur along major fault lines on Earths crust.


Mount Vesuvius in Italy erupted so violently in A.D. 79 that it covered the city of Pompeii in twenty feet of ash and small pebbles. Its last eruption was in 1944.

The materials that a volcano sends into the air can affect world weather patterns. Dust can block the sunlight, allowing less heat to pass through the air. That harms crops. Less sunlight can mean colder winters. However, the soil around volcanoes can be rich in minerals, which is good for farming.

In San Francisco, the Hayward Fault can generate both minor earthquakes and earthquakes that are strong enough to damage anything above it.

Earth is constantly changing. Changes can happen over many years through erosion and deposition, or they can happen quickly because of volcanoes and earthquakes. Imagine how different Earth might look a thousand years from now!

Earthquake and Volcano Effects

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Glossarydeposition the process in which pieces of Earths surface are laid down to build up new areas

earthquake a shaking or sliding of a portion of the Earths crust, caused by the sudden movement of masses of rock along a fault

epicenter the point on Earths surface directly above the focus of an earthquake

erosion the process in which weathered rock and soil are moved to a new place

fault a crack or separation in Earths crust

landforms natural physical features of Earths crust

landslide rapid downhill movement of rock and soil materials

volcano an opening in Earths crust where lava, ash and gases erupt onto the surface and into the atmosphere

weathering the process in which rocks break down into smaller pieces

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1. What is physical weathering? Give two examples of it.

2. How can the effects of erosion be limited?

3. What can trigger an avalanche?

4. Volcanoes can cause extensive damage. Write to explain why volcanoes are so destructive. Include details from the book to support your answer.

5. Compare and Contrast What are some similarities between earthquakes and volcanoes? What are some differences?

What did you learn?Vocabularydepositionearthquakeepicentererosionfaultlandformslandslidevolcanoweathering

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: Getty Images; 1 Getty Images; 2 (BL) Getty Images; 3 (BR) Getty Images, (CR) Comstock Inc.;4 (BL) Getty Images, (CR) Digital Stock; 5 Getty Images; 6 Getty Images;7 (BR, CR) Getty Images, (T) Yann Arthus-Bertrand/Corbis; 8 (T) /Corbis, (BL) Getty Images; 9 Getty Images;10 (BL) Getty Images, (R) Galen Rowell/Corbis; 11 (BR) Getty Images, (BL) Niall Benvie /Nature Picture Library;12 (BL) Getty Images, (C) Digital Stock; 13 (BR) Getty Images, (BC) Bembaron Jeremy/Corbis Sygma;14 (BL) Getty Images; 15 (BR) Getty Images, (BC) Roger Ressmeyer/Corbis; 16 Getty Images.

Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson.

ISBN: 0-328-13884-3

Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,mechanical, photocopying, recording, or likewise. For information regarding permission(s), write toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

13884_01-04_CVR_FSD.indd Cover213884_01-04_CVR_FSD.indd Cover2 5/12/05 7:09:55 PM5/12/05 7:09:55 PM

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