4 9 changing surface of the earth (earth science)

Vocabulary deposition earthquake epicenter erosion fault landforms landslide volcano weathering Picture Credits Every effort has been made to secure permission and provide appropriate cr

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Scott Foresman Science 4.9

Nonfi ction Compare and

Contrast

• Captions

• Labels

• Diagram

• Glossary

Earth’s Surface

ISBN 0-328-13884-3

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Scott Foresman Science 4.9

Nonfi ction Compare and

Contrast

• Captions

• Labels

• Diagram

• Glossary

Earth’s Surface

ISBN 0-328-13884-3

ì<(sk$m)=bdiief< +^-Ä-U-Ä-U

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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?

extensive damage Write to explain why volcanoes are so destructive Include details from the book to support your answer

similarities between earthquakes and volcanoes? What are some differences?

What did you learn?

Vocabulary

deposition

earthquake

epicenter

erosion

fault

landforms

landslide

volcano

weathering

Picture Credits

Every 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.

ISBN: 0-328-13884-3

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 to

Permissions 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

by Lorrie Oestreicher

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How Earth’s

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

Earth’s Crust

The part of Earth we see is actually a very thin layer

of rock called the crust You can’t see Earth’s crust in the

ocean because it is deep below the surface

Earth’s natural features are called landforms A

canyon is one shape that Earth’s 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 areas—

they all vary in size, shape,

and age How were they

formed? How do these

landforms change?

Weathering

The 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 Weathering

Physical 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 Weathering

Chemical 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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Deposition

Wind 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 Earth’s 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

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Avalanches 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 Earth’s Surface

Changes Rapidly

Volcanoes

Volcanoes and earthquakes bring about

very fast changes to Earth’s 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 Earth’s crust This is

called a volcano A volcano erupts when the magma

reaches the surface Magma that escapes onto Earth’s

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

13

This entire street as well

as the car are covered in volcanic dust.

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Earth’s 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 Earth’s 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

Earth’s 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 Earth’s 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

focus

epicenter

crust mantle shock wave

Earthquakes occur along

major fault lines on

Earth’s 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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deposition the process in which pieces of Earth’s

surface are laid down to build up new areas

earthquake a shaking or sliding of a portion of the

Earth’s crust, caused by the sudden movement of masses of rock along a fault

epicenter the point on Earth’s 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 Earth’s crust

landforms natural physical features of Earth’s crust

landslide rapid downhill movement of rock and

soil materials

volcano an opening in Earth’s 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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