4 9 changing surface of the earth (earth science)

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Earth’s Surface

Scott Foresman Science 4.9

ISBN 0-328-13884-3

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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.
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 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

What did you learn?
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
by Lorrie Oestreicher
volcanoes? What are some differences?


How Earth’s
Surface
Changes

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!

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

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?
High areas, low areas,
flat areas, rugged areas—
they all vary in size, shape,
and age. How were they
formed? How do these
landforms change?
island

2

canyon

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.
stream

3


Physical Weathering

Chemical 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.

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
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.

4

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

5


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

Erosion
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 flows 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 flow
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.

6

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.

7


aerial view of
the Mississippi
River delta

Wind cannot carry as much material as flowing
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.

Landslides

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 flowing
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.

8

No place on Earth is completely flat. 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
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.

9


Avalanches
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.

10

How to Control Erosion
And Deposition
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.

11


How Earth’s Surface
Changes Rapidly
Volcanoes and earthquakes bring about
very fast changes to Earth’s surface.

Volcanoes
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.

After an Eruption
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 flying two miles into the air.
A nearby city was covered in volcanic dust. The eruption
sent lava running down the sides of the volcano.

Active and Dormant Volcanoes
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 first 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.

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

12

13


Earthquakes occur along
major fault lines on
Earth’s crust.

Earthquake and Volcano Effects

fault line

epicenter

Earthquakes

focus

shock wave

crust

mantle

Earth’s crust floats 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.

14

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!

15


What did you learn?

Vocabulary

deposition
Glossary
earthquake
epicenter
deposition
the process in which pieces of Earth’s
erosion
surface are laid down to build up new areas
fault
landforms a shaking or sliding of a portion of the
earthquake
landslide Earth’s crust, caused by the sudden
volcano
movement of masses of rock along a fault
weathering
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

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.

landslide

rapid downhill movement of rock and
soil materials
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.

volcano

an opening in Earth’s crust where lava, ash
and gases erupt onto the surface and into
the atmosphere

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

weathering the process in which rocks break down into
smaller pieces
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 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

16

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?