KEY CONCEPT
Glaciers carve land and
move sediments.
Sunshine State
STANDARDS
SC.D.1.3.1: The student
knows that mechanical
and chemical activities
shape and reshape the
Earth’s land surface by
eroding rock and soil
in some areas and
depositing them in
other areas, sometimes
in seasonal layers.
BEFORE, you learned
NOW, you will learn
• Running water shapes
landscapes
• Wind changes landforms
• How moving ice erodes land
• How moving ice deposits
sediment and changes
landforms
EXPLORE Glaciers
How do glaciers affect land?
VOCABULARY
glacier p. 281
till p. 284
moraine p. 284
kettle lake p. 285
PROCEDURE
1
MATERIALS
Flatten the clay on top of a paper towel.
2 Drag the ice cube across the clay as shown.
Record your observations.
3 Leave the ice cube to melt on top
• modeling clay
• paper towel
• ice cube
containing
sand and gravel
of the clay.
WHAT DO YOU THINK?
• What happened when you dragged
the ice cube across the clay?
• What happened to the sand and
gravel in the ice cube as it melted?
Glaciers are moving bodies of ice.
VOCABULARY
Remember to add a
four square diagram for
glacier to your notebook.
You might not think of ice as something that moves. But think about
what happens to an ice cube on a table. The cube begins to melt,
makes a small puddle, and may slide a little. The water under the cube
makes the table surface slippery, which allows the ice cube to slide.
A similar process happens on a much larger scale with glaciers.
A glacier is a large mass of ice that moves over land. A glacier forms
in a cold region when more snow falls than melts each year. As the
snow builds up, its weight presses the snow on the bottom into ice.
On a mountain, the weight of a heavy mass of ice causes it to flow
downward, usually slowly. On flatter land, the ice spreads out as a
sheet. As glaciers form, move, and melt away, they shape landscapes.
Chapter 8: Erosion and Deposition 281
Extent of Glaciers
Glaciers can exist only in places where it is cold enough for water to
stay frozen year round. Glaciers are found in mountain ranges all over
the world and in land regions near the north and
Ice Age in North America
south poles.
ICELAND
GREENLAND
NORTH
AMERICA
Maximum extent of ice
coverage during the
Pleistocene Epoch
RESOURCE CENTER
CLASSZONE.COM
Learn more about the
movement and effects
of glaciers.
Today, glaciers cover about 10 percent of Earth’s
land surface. However, the amount of land surface
covered by glaciers has varied greatly over Earth’s
history. Glaciers have expanded during long cold
periods called ice ages and have disappeared during
long warm periods. About 30,000 years ago—during
the last major ice age—glaciers extended across
the northern parts of North America and Eurasia.
They covered nearly 30 percent of the present land
surface of Earth.
There are two major types of glaciers: alpine
glaciers and continental glaciers.
Alpine Glaciers
Alpine glaciers, also called valley glaciers, form in mountains and flow
down through valleys. As these glaciers move, they cause erosion,
breaking up rock and carrying and pushing away the resulting sediment.
Over time, an alpine glacier can change a V-shaped mountain valley
into a U-shaped valley with a wider, flatter bottom.
Some glaciers extend all the way down into the lower land at the
bases of mountains. At an alpine glacier’s lower end, where temperatures
are warmer, melting can occur. The melting glacier drops sediment,
and streams flowing from the glacier carry some of the sediment away.
If an alpine glacier flows into the ocean, big blocks may break off and
become icebergs.
Continental Glaciers
Continental glaciers, also called ice sheets, are much larger than alpine
glaciers. They can cover entire continents, including all but the highest
mountain peaks. An ice sheet covered most of Canada and the northern
United States during the last ice age. This ice sheet melted and shrank
about 10,000 years ago.
Today, ice sheets cover most of Greenland and Antarctica. Each
of these glaciers is shaped like a wide dome over the land. The ice on
Antarctica is as much as 4500 meters (15,000 ft) thick.
Check Your Reading
282 Unit 2: Earth’s Surface
What are the two major types of glaciers and where do
they form?
Types of Glaciers and Movement
A glacier is a large mass of ice that moves
over land.
Alpine Glaciers
Continental Glaciers
A glacier, such as this one in Alaska, changes the
landscape as it moves down a mountain valley.
Huge sheets of ice cover the continent of Antarctica
and other land regions.
Glacier Movement
Gravity causes the ice in a glacier to move downhill. Two different processes cause glaciers to move: flowing and sliding.
Flowing The ice near the surface of a glacier is brittle, and cracks often form in it. However, deep inside a
glacier, ice does not break as easily because it is under
great pressure from the weight of the ice above it.
Instead of breaking, ice inside a glacier flows like
toothpaste being squeezed in its tube.
As a glacier moves, it
breaks up rock and pushes
and carries sediment.
Sliding The weight of a glacier and heat from Earth
cause ice at the bottom of a glacier to melt. A layer of
water forms under the glacier. The glacier slides along
on this layer of water just as an ice cube might slide
on a countertop.
In the illustration, why are cracks shown near the surface of the glacier
and not at the bottom?
Chapter 8: Erosion and Deposition 283
Glaciers deposit large amounts of sediment.
abrasion
A moving glacier left
visible abrasion lines on
this rock.
As glaciers have melted and retreated, they have shaped the landscapes
of many places on Earth. As a glacier moves or expands, it transports a
vast amount of sediment—a mix of boulders, small rocks, sand, and
clay. It acts like a plow, pushing rock and soil and plucking out big
blocks of rock. As a glacier moves over rock, it scratches and scrapes
the rock in a process called abrasion. Abrasion leaves visible grooves
on rock surfaces.
Moraines
When glaciers expand and advance and then melt and retreat, they
affect both the land underneath them and the land around them. A
glacier pushes huge amounts of sediment to its sides and front. When
the glacier retreats, the deposits of sediment remain as visible evidence
that ice once moved through. The sediment left directly on the ground
surface by a retreating glacier is called till.
A deposit of till left behind by a retreating glacier is called a
moraine (muh-RAYN). The ridges of till deposited at the sides of a
glacier are called lateral moraines. The till that marks the farthest
advance of a glacier forms a deposit called an end moraine. Moraines
formed by continental glaciers, such as those in North America during
the ice age, can be huge—many kilometers long.
A glacier scooped out this
valley in California and
left behind lateral
moraines.
The blanket of till that a glacier deposits along its bottom is called
a ground moraine. Rock deposits from glaciers can often be identified
as till because the till rocks are different, in type or age, from the rock
that was present before the glacier formed.
Check Your Reading
Draw a sketch of a glacier and label where lateral, end, and
ground moraines would form.
Lateral moraines
284 Unit 2: Earth’s Surface
Lakes
Besides ridges, hills, and blankets of till, melting glaciers also leave
behind depressions of various sizes that can become lakes. Landscapes
shaped by glaciers are often dotted with small kettle lakes as well as larger
lakes. A kettle lake is a bowl-shaped depression that was formed by a
block of ice from a glacier and then became filled with water.
1
2
As a glacier moves away, it
leaves huge blocks of ice.
Over time, sediment builds up
around the ice.
3
The ice melts, leaving behind bowls that
become kettle lakes. These lakes are
in Wisconsin.
The last ice sheet in North America formed many kettle lakes
in some regions. Kettle lakes are common in Michigan, Wisconsin,
and Minnesota.
Kettle Lake Formation
How do kettle lakes form?
Kettle lakes form when sediment builds up around
blocks of ice left behind by a retreating glacier.
Use what you know about kettle lake formation
to design a model of the process.
PROCEDURE
1
Use the tray, the ice cubes, and the other materials to model how sediment
builds up around ice blocks.
2 Write a description of the process you used to make your model.
SKILL FOCUS
Designing
models
MATERIALS
•
•
•
•
•
•
shallow tray
ice cubes
modeling clay
sand
gravel
water
TIME
30 minutes
WHAT DO YOU THINK?
• Describe how your model worked. What did you do first? What happened next?
• Did your model accurately represent the formation of kettle lakes? Did it
work? Why or why not?
• What were the limitations of your model? Are there
any aspects of kettle lake formation that are not
represented? If so, what are they?
285
Great Lakes Formation
2
14,000 Years Ago
3
7000 Years Ago
Today
Superio
ICE
ICE
M
ic
hi
ga
r
n
H
1
ur
on
St. Lawrence
River
Ontari
o
Erie
The ice sheet covering a land of
river valleys began to retreat.
Water filled the bowls carved out
by the ice.
The Great Lakes contain 20 percent
of the world’s fresh lake water.
Many large lakes are the result of ice ages. In some places, lakes
formed after glaciers in valleys melted and left behind moraines that
dammed the valleys. Many of these lakes are long and narrow, like the
Finger Lakes in New York, which are named for their slender shape.
The Great Lakes were formed thousands of years ago as an ice
sheet moved over the land and then melted. A million years ago, the
region of the Great Lakes had many river valleys. The ice sheet gouged
out large depressions in the land and left piles of rock and debris that
blocked water from draining out. In some areas, where the deepest
Great Lakes are now, the enormous weight of the glacier actually
caused the land to sink as much as one kilometer.
The ice sheet started to melt about 14,000 years ago. By about 7000
years ago, it had melted past what would become Lake Erie and Lake
Ontario, the lakes farthest to the east.
check your reading
What are two ways the ice sheet formed the Great Lakes?
KEY CONCEPTS
CRITICAL THINKING
1. Describe the two processes
that cause glaciers to move.
4. Compare and Contrast
Identify two ways in which the
erosion effects of glaciers differ
from those of rivers.
2. What are the two major types
of glaciers, and where are
they found?
3. Describe the land features left
behind by glaciers that have
melted and shrunk.
286 Unit 2: Earth’s Surface
5. Predict How would glaciers
be affected by changes in
climate, such as global
warming and global cooling?
CHALLENGE
6. Infer Regions near the equator
are generally the warmest on
Earth. However, in one small
area of Africa, there are
glaciers close to the equator.
Form a hypothesis to explain
why these glaciers exist.