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Glaciation Processes |
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What is a Glacier ?
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•A
glacier is a large amount of ice which flows very slowly.
•A
glacier is made when lots of snow gets squashed into ice and
then slides downhill.
•The
ice goes down the easiest route so it follows old river
valleys down from the mountains.
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What is the glacier system?
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Inputs
come from avalanches along the sides of the glacier but
mainly from precipitation as snow.
Over time snow accumulates and is compressed into
ice. The water held in
storage
is the glacier.
Under the force of gravity, the glacier
flows
downhill.
Meltwater is the main output
from the glacier, along with some
evaporation.
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Accumulation and ablation
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The balance
between inputs and outputs varies.
In the winter,
inputs usually exceed outputs near to the head of a glacier
(accumulation).
In the summer and
at lower altitudes, outputs will exceed inputs (ablation).
The balance
between the annual rate of accumulation and ablation
determines whether the glacier will advance or retreat.
Today, most of
the world’s remaining glaciers are retreating.
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How do
glaciers erode?
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Abrasion
The moraine
frozen into the glacier scours the valley sides and base.
This is a sandpapering effect, similar to corrasion by a
river but on a far larger scale.
Abrasion is the process of a glacier scouring the surface it is moving over. Rocks beneath the surface may be ground up or polished. Glaciers may leave long scratches or grooves called striations in the rock. |
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Plucking
The water at the
bottom of the glacier freezes onto rock on the valley base.
As the glacier moves, the rock is pulled away from the
valley base. Plucking mainly occurs when the rock is
well-jointed.
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