Transcript Glacial Erosion

GLACIERS
A glacier is:
 Any large mass of ice that moves
slowly over land
Two Kinds of Glaciers
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Valley glacier – a long narrow glacier
that forms when snow and ice build up
high in a mountain valley
Continental glacier – a glacier that
covers much of a continent or large
island
Valley Glaciers
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Found in high mountain ranges such
as the Rockies, Alps, and Himalayas
These glaciers move down valleys that
have already been cut by rivers
Continental Glaciers
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Much larger than valley glaciers
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Cover about 10 percent of Earth’s land
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Examples: Antarctica and most of
Greenland are covered by continental
glaciers
How Glaciers Form…
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A glacier can only form in an area where
more snow falls than melts. This is because
the temperatures seldom rise above
freezing and layers and layers of snow
compact into ice.
Once the depth of snow and ice reaches
more than 30 to 40 meters, gravity begins
to pull the glacier down.
How Glaciers Move…
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Valley glaciers flow at a rate of a few
centimeters to a few meters per day.
Sometimes, a valley glacier slides
down more quickly in what is called a
surge.
Continental glaciers can flow in all
directions and spread out much as
pancake batter spreads out in a frying
pan.
Two Processes of Glacial
Erosion…
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Plucking – as a glacier flows over the land,
it picks up rocks; the weight of the ice
breaks the rocks apart and they freeze to
the bottom of the glacier
Abrasion – the many rocks that remain on
the bottom of the glacier get dragged
across the land, causing gouges and
scratches in the bedrock
Glacial Deposition
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When a glacier melts, it deposits the
sediment it eroded from the land, creating
various landforms.
The mixture of sediments that a glacier
deposits directly on the surface is called till.
Clay, silt, sand, gravel, and boulders can all
be found in till.
Glacial Deposition
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A moraine forms when the till is
deposited at the edges of a glacier and
forms a ridge
It is made up of a mixture of particles
of different sizes: from sand and
gravel to boulders.
History of the Great Lakes
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The continental glacier of the last ice age formed
the Great Lakes.
Before the ice age, there were large river valleys in
the area now occupied by the lakes.
As the ice advanced over these valleys, it scooped
out loose sediment and soft rock, forming broad,
deep basins.
The Great Lakes formed over thousands of years as
the glaciers melted and the basins filled with water.
Videos about Glaciers
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Watch the following video segments. Click
on the hyperlink below to go to the
videos.
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Glacial Erosion
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Tumble Glacier Video
Exploring Glacial
Landforms
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Go to pages 92-93 in your textbook.
Study the glacial landforms pictures
and answer the questions on your
sheet.