GLACIAL EROSION AND DEPOSITION
GLACIAL EROSION
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As glaciers travel over land, glacial ice can erode the underlying
bedrock.
This erosion can happen by:
 Plucking
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Abrasion
PLUCKING
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This occurs when melt water at the
base of the glacier freezes in
cracks and fractures the
underlying bedrock.
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The fractured materials are then
pulled away from the bedrock.
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The weathered material then
becomes incorporated into the
glacial ice and undergoes
transportation as the glacier
moves.
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Glacial ice also picks up loose
boulders , pebbles, and sand from
the underlying surface as it moves.
ABRASION
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This is the grinding or scouring of
exposed rock surfaces by rock
fragments embedded in the base of the
glacier.
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Think of this a being the sandpaper effect
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The dislodged pieces of rock become
part of the glacial ice.
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The abraded bedrock surfaces generally
show a polished look and display
striations or grooves caused by the
sediment embedded in glacial ice.
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The abraded material can become
pulverized to yield a fine clay or silt
material called rock flour
CONTOURS
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Continental glaciers only erode on the bottom, and just flatten
out the topography
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Valley glaciers erode along their sides and on the bottom.
The shape of the valley as the glacier moves downhill is that of
a U-shape or glacial trough.
These valley glacier give us many unique features based on the
size and location.
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Fjords
Hanging valleys
Cirques
Horns
Arêtes
Fjords
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Glacial formed valleys filled with seawater.
Hanging valleys
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A U-shaped valley not as deep as the main valley.
Cirques
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A three sided bowl shaped depression where valley glaciers
begin.
Horns
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A sharp mountain peak formed adjoining cirques
Arêtes
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Sharp ridges which join adjacent horns and adjacent cirques
DEPOSITION
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The material moved by a glacier eventually is deposited as the
glacier melts.
All sediment that is deposited by a glacier is termed glacial
drift.
There are two types of glacial drift:
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Till, and
Outwash
TILL
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This is the material that is deposited directly by glacial ice and
is a mix of sediment particles of various sizes.
Large boulders of drift that are moved far from their bedrock
source are called erratics.
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As a valley glacier moves downhill, it erodes material at the
glacier’s sides and base and forms distinct features made of
till. These features are called moraines.
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End Moraine – contains the glacial till at the toe of a glacier
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Ground Moraine – are a term for a moraine at the base of the
glacier
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Lateral Moraines – are the deposited till along the sides of a
glacier.
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When two glacier with lateral moraines merge their lateral
moraines join in the center of the merged glacier to form
medial moraines in the central portion of the glacier
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Till deposited at the base of a glacier can be reshaped by
successive glacial movements into streamlined mounds of till
called drumlins.
OUTWASH
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This is material that deposited by melt water from a glacier and
is similar to a stream deposit, with larger fragments deposited
by waters flowing with greater velocity and finer fragments
deposited by slower moving water.
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During warm weather or periods of retreat, glaciers discharge
melt water at their toe or terminus. The area created by the
deposition of sediment from flowing melt water from a glacier is
called the outwash plain.
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Melt water can form a meandering streams at the base of a
glacier. These streams create sinuous ridges of sediment
called eskers.
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During a retreat a large chunk of ice remains behind which
depresses the land and melts to form a kettle lake.
Esker located in SW Nova Scotia
Kettle lakes