3
How Do Glaciers and Wind
Cause Erosion?
LESSON COALS
You will learn
• how glaciers cause
erosion and deposition.
• how wind causes erosion
and deposition.
glacier (gla/shor), a large,
slow-moving mass of ice.
Look at the mountains below. Even though you
cannot see any streams, erosion is happening there.
The ice on the mountains is moving sediments.
Glaciers and Erosion
Imagine snow falling on a mountain on a cold da)'.
The temperature stays near freezing that day, and
during the rest of the year-and then for many years.
Each year, new snow falls on old snow. The heavy
new snow on top packs the old snow below into ice.
After many years, gravity causes the ice to begin
moving. The ice moves down the mountain very,
very slowly. A glacier has formed. As the glacier
moves, rocks and soil become buried in its bottom
and edges. What do you think happens when these
rocks grind against land as the glacier moves?
Glacier
250
There are two main kinds of glaciers. One kind is a
sheet of ice that can cover thousands of square
kilometers of land. The other kind of glacier forms in
mountains. A mountain glacier looks like a frozen
river. Which kind of glacier is shown below?
Sheets of ice once covered much of the world.
These huge glaciers formed during the last ice age.
An ice age is a period of-thousands of years when
snow and ice cover much of the land.
During the last ice age, the weather warmed and
cooled many times. Glaciers formed in cold years. As
the ice moved, it weathered mountains into round
hills. In many areas, glaciers scraped land flat and
carried away rock and soil. In warm years, the ice
melted and deposited huge hills of rock and soil. The
picture to the right shows such rocks. Holes dug by
glaciers filled with water as the ice melted, forming
the Great Lakes. Thousands of small lakes formed in
what is now Wisconsin and Minnesota.
SCIENCE IN YOUR LIfE
Today, glaciers cover
about 1110 of the earth's
crust. However, some
scientists who study
weather patterns conclude
that another ice age will
happen. Perhaps thousands
of years from now, great
sheets of ice will form
again and co/er much of
the world.
ice age, a period of
thousands of years when
snow and ice cover much
of the earth.
,
251
SCIENCE IN YOUR LIFE
Planting rows of trees
can slow wind erosion.
The rows of trees, or
windbreaks, slow down the
wind. Then the wind
cannot pick up so much
soil. Many farmers leave
stubs of plants in fields
until new crops are
planted. The plant roots
hold the loose soil in place
and protect it from strong
winds.
Rocks carved out by wind
252
Wind Causes Erosion
Have you ever felt bits of sand or dirt hit your skin
on a windy day? Wind changes the earth's crust by
moving soil and sand. Wind can carry sand grains and
blow them against rocks. Look at the rocks in the
picture below left. Windblown sand has battered the
rocks, carving out the grooves you see. Given enough
time, this sandblasting can destroy a lar e roek.
When winds slow down, deposition occurs as
sediments drop to the ground. The heaviest-pieces
drop first, just as they do in a stream when the water
slows down. In time, large amounts of sediment can
build up. Notice the dune below. This dune is a hill of
wind-eroded sand.
Besides building dunes, winds also move dunes.
Winds can move a dune as much as 5 to 9 meters a
year. The dune in the picture below is slowly
moving. What change is happening because of the
slow movement?
Dune burying a forest
Over time, wind can remove most of the sand and
soil in an area. This loss of soil often happens in
desert areas where few plants grow to hold the soil
down. The picture below shows how the ground
looks in such a place. Why can this kind of wind
erosion be very serious in farming areas?
Lesson Review
1. How do glaciers cause erosion and deposition?
2. How does wind cause erosion and deposition?
3. Challenge! How do you think the speed of wind
.affccts weathering and erosion?
Study on your own, pages 422-423.
I
Wind has stripped the soil from this place.
Write to your state's Soil Conservation
Service office to find out about soil erosion
problems in your state. Ask how scientists, city
planners, farmers, and others work to control soil
erosion in your state. Write a report explaining
what you learn.
FIND OUT
ON YOUR OWN
253
LESSON 3
pages 250-253
1. What is a glacier?
2. What are the two kinds of glaciers?
3. An mm is a period of thousands of years when snow and
ice covers much.of the land.
4. The Wit were formed by the melted ice from glaciers.
5. What happens when wind carrying sand and rocks slows?
6. What are dunes?
7. How can dunes move?