Lesson 1 What
Are Weathering and Erosion?
Fast Fact
Rising Seas The Giant's Causeway, in Ireland, is made of basalt, which can form fiveor six-sided columns as it cools and shrinks. The sea is wearing away these cliffs.
In the Investigate, you'll get an up-close look at one way rock breaks down.
Shake Things Up
Materials
 6 medium-sized rocks
 2 pieces of chalk
 empty clear plastic juice container with lid (2 qts)
Procedure
1. Make a model of the way rocks break down in nature. Add two pieces of chalk to the
container.
2. Place six rocks in the container.
3. Put the lid on the container.
4. Shake the container so that the rocks and chalk rub against each other. Do this for
several minutes. You can take turns with your lab partner.
Draw Conclusions
1. Compare the ways the rocks and chalk looked at the start and at the end of the
investigation.
2. Inquiry Skill Scientists often infer the reasons for an investigation's results. Why do
you think some of the materials in the container broke down faster than other
materials? How do you think this relates to rocks in nature?
Investigate Further
First, weigh the chalk that is left after the investigation. Then, add water to the
container and repeat the test. Compare the mass of the chalk before and after
the water. What conclusion can you draw?
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Reading in Science
VOCABULARY
weathering p. 198
erosion p. 202
SCIENCE CONCEPTS
 how weathering affects rock
 how erosion affects rock
READING FOCUS SKILL
CAUSE AND EFFECT Look for the causes of weathering.
Weathering
Have you ever seen a weed growing through a crack in a sidewalk? Maybe you've seen
a statue with its features worn away. These are examples of weathering.
Weathering is the breaking down of rock on Earth's surface into smaller pieces.
Weathering helps shape landforms. It also helps make soil.
There are two types of weathering. One type of weathering physically breaks rock into
smaller pieces.
The other type of weathering changes the chemical makeup of rock. This softens and
weakens the rock, helping water wear it away. Water causes most weathering. It
can break down some rock by itself. For example, water can wear away rock salt,
calcite, and limestone.
Sinkholes are the result of weathering. They form when water slowly dissolves
underground rock.
---see pictures
Water can help wear away bits of surface rock.
A chemical change has turned the surface of this rock brown. Iron oxide, or rust,
breaks down the outer layer of some kinds of rock.
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Some rocks break down when oxygen combines with minerals in them. This often
happens in rocks that have iron. When iron mixes with oxygen, iron oxide, or rust,
forms. Rust makes it easier for other processes to weather the rock.
CAUSE AND EFFECT What is the effect of weathering?
Science Up Close
Formation of a Sinkhole
1. Rain soaks into the ground. The rainwater dissolves limestone rock under the
surface. Water carries away the dissolved rock. A small opening forms.
2. The opening in the rock becomes larger as time passes.
3. Rock and soil that covered the underground opening cave in. A sinkhole forms
on the surface. Do you think this process happens quickly or slowly? Explain.
---see picture
This 15-story-deep sinkhole formed in Florida in 1994. It formed in an area where
large amounts of minerals were taken out of the ground.
For more links and activities, go to www.hspscience.com
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Weathering by Other Processes
Physical weathering doesn't change the rock chemically. It breaks rock down through
physical processes. Water, ice, living things, and wind are causes of this type of
weathering.
You see the results of this weathering around you each day. It can cause cracks in
sidewalks and potholes in streets. Rain enters cracks in rock and cement. If the
water freezes into ice, it expands. The ice cracks and breaks rock around it. Stones
in streams are also a sign of weathering. These stones were broken from larger
pieces of rock. As they tumble against each other, they break down even more.
Large ocean waves weather coastlines. Waves smash into the bottom of a cliff. The rock
that the waves hit cracks and breaks. In time, rock at the top of the cliff falls into
the sea.
Even temperature changes can weather rock. Rock expands when it heats up. It
contracts when it cools. Repeated heating and cooling can
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weaken some rock. The rock can then crack or break.
Living things can cause weathering. You have probably seen plants grow through
cracks in rocks. The roots wedge into the rocks, splitting the rock around them as
they grow. Animals can cause weathering, too. When animals dig in soil, they
move rocks closer to Earth's surface. Then rainwater can reach them more easily.
Wind also causes weathering. Wind picks up bits of rock and soil and throws them
against other rocks. This chips away the rocks' surface bit by bit.
---see pictures pg. 200
Pounding waves force air into cracks. This helps split the rock. Water also carries
sediment. This scrapes rock as sandpaper scrapes wood.
Waves hit cliffs like this with great force. Thousands of tons of water smash into
coastal rocks during storms.
---see pictures pg. 201
Running water carries sediment. The sediment scrapes against itself and against
rocks in the streambed as the water moves.
Scraping and bumping against each other in a moving stream gives these rocks
rounded edges.
CAUSE AND EFFECT How does ice cause weathering?
Insta-Lab
Observe Weathering
Use a large rock or brick to press down on a handful of rock salt. What happens to the
rock salt? What kind of weathering does this model?
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Erosion
What happens after weathering breaks down rock into sediment? Erosion takes over.
Erosion is the process of moving sediment.
Water can cause erosion. Rivers carry sediment downstream. They drop it on their
banks or at their mouths. Ocean waves pick up sediment and leave it on the shore
as sand.
Wind erosion is most common in deserts. With few plants to hold sediment in place,
wind picks it up easily. Wind stacks sand into huge mounds called sand dunes.
Glaciers are important causes of erosion. As these giant sheets of ice move, they scrape
the ground. They pick up rocks and soil. During the last Ice Age, huge glaciers
covered large parts of what is now the northern United States. As glaciers moved
over land, they helped shape the plains and other landforms we see today. When
the glaciers melted, they formed lakes. They left behind huge ridges of sediment
and large amounts of water.
CAUSE AND EFFECT What are the main causes of erosion?
Math in Science
Interpret Data
What is the largest type of sediment? What is the smallest? Which would erosion affect
more, boulders and cobbles or silt and clay? Why is that?
---see chart
Water that washes over areas of bare soil can create gullies. Planting vegetation
can help prevent this type of soil erosion.
This photo shows one river flowing into another. Soil washes into rivers from areas
along its banks. One of these rivers is carrying much more sediment than the
other. The sediment has turned parts of the water brown.
---see pictures
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Reading Review
1. CAUSE AND EFFECT Copy and complete the graphic organizer below.
---see chart
2. SUMMARIZE Summarize the lesson section on physical weathering.
3. DRAW CONCLUSIONS The Colorado River flows through the bottom of the
Grand Canyon. Does the river cause weathering or erosion? Explain.
4. VOCABULARY Make a crossword puzzle using the vocabulary for the three
lessons in this chapter.
Test Prep
5. Critical Thinking You see a marble sign. Its letters are too worn to read. What
caused this?
6. Which of these doesn't cause weathering?
A. wind
B. magma
C. water
D. plants
Writing
Narrative Writing
Write the story of a grain of sediment that has been weathered from a mountain, carried
to the sea by a river, and left on a beach. Write from the sediment's point of view.
Math
Solve Problems
A farmer plants of his land with trees to stop erosion. If he plants trees on 525 hectares,
how much land does he have? Show your work.
Social Studies
Famous Features
Research a famous natural feature, such as a canyon, mountain, or rock formation.
Explain how it formed. Draw a map that shows where the feature is located. Share
with the class what you find.
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