Glaciation

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Glaciation
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http//pubs.usgs.gov/factsheet/fs133-99/worldmap.g
if
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• about 15 million square kilometres of the earths
  surface are covered with glaciers
• two types - alpine and continental
• Greenland and Antarctica both have continental
  glaciation
• continental glaciation is found at high
  latitudes alpine is found at high altitudes

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• How glaciers form
• two basic conditions are necessary for
  glaciation (1) prolonged cold (2) ample snow
• over time the overlying layers of snow cause the
  lower layers of snow to recrystallize (refreeze)
  and the pore space is reduced, ie., the snow
  becomes denser

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• at the end of the winter, the snow that is left
  is called neve and it is about 50 pore space
• if the snow survives the summer it is called firn.

http//craton.geol.brocku.ca/faculty/rc/teaching/1
F90/glaciers/figure141.html
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• it is called glacier ice when the pore space is
  reduced to about 5 and it is impervious to water
• after about 50 to 60m of ice has been accumulated
  the pressure of the overlying layers causes the
  ice to flow outwards from the center of
  accumulation - this will happen sooner (thinner)
  on a slope
• glaciers move through a combination of flowing
  (properly called internal deformation) and
  sliding across the surface (called basal slip)

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• flow velocity of a glacier is greatest near the
  surface and in the middle of the glacier, just
  like water in a river

Above
Side
http//www.physicalgeography.net/fundamentals/10ae
.html
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How ice erodes 1. scraps or scours - like
sandpaper - rocks are embedded into the bottom of
the ice sheet and erode the bedrock as it
flows 2. conveyor belt - embedded rocks are
carried in the ice and deposited in the front as
the glacier flows
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3. plucking - ice freezes onto the rock and pulls
or plucks it away as it flows 4. bulldozer -
material is pushed along in front
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• Mass balance
• glaciers are in a state of mass balance meaning
  that the rate of accumulation of ice is balanced
  by the rate of ablation (melting)
• note that ice is transferred from the zone of
  accumulation to the zone of ablation by mainly by
  flowing

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• a simple glacier is therefore a system in a state
  of dynamic equilibrium, which is easily upset by
  changes in annual rates of nourishment or wastage
  of ice

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http//www.physicalgeography.net/fundamentals/10ae
.html
Ice transfers from the Zone of Accumulation to
the Zone of Ablation by flowing.
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Animation showing the vertical growth of a ice to
60 metres thickness, after which the ice flows
outward from its centre as a glacier.
http//craton.geol.brocku.ca/faculty/rc/teaching/1
F90/glaciers/glacan.html
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• If, over an extended period of time, the rate of
  accumulation of ice is greater than the rate of
  ablation, the mass of the glacier will increase
  and the glacier will advance.
• If the rate of ablation is greater than the rate
  of accumulation, the mass of the glacier will
  decrease and the glacier will retreat.

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The advance and retreat of a glacier depends on
the balance between accumulation of snow (gray)
and ice (blue) in the accumulation zone and the
melting of ice in the zone of wastage.
http//craton.geol.brocku.ca/faculty/rc/teaching/1
F90/glaciers/glacieranimation.html
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• the main inputs to a glacial system are water, in
  the form of snow, and eroded sediments that are
  picked up by the moving ice.
• water leaves the glacial system when ice is
  converted into liquid water or water vapour

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• sediment leaves a glacial system at the base of
  the glacier as till and at its terminal end (the
  terminus) as moraines or as material that gets
  reworked by glaciofluvial process (the water
  flowing off the glacier).

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• glacier ice is lost by melting, evaporation, and
  sublimination.
• ice can also be lost through calving when ice
  bergs break off in large bodies of water happens
  a lot from Greenland and Antarctic glacier
  sheets.
• view Quicktime movies of ice advance and retreat
  see the links at
• http//www.physicalgeography.net/fundamentals/10ae.
  html