Glaciation

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Glaciation
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Key understandings Difference between alpine and
continental glaciation. How glaciers form
recystallization. How glaciers erode the
surface. The concept of mass balance of a
glacier. Ice ages.
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Introduction

• ice is one of the hardest substances on Earth
• the power not only to sink the Titanic, but also
  to transform the shape of the land

http//www1.istockphoto.com/file_thumbview_approve
/3138731/2/istockphoto_3138731_alpine_glacier.jpg
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• about 15 million square kilometres of the earths
  surface are covered with glaciers
• two types - alpine and continental
• continental glaciation is found at high
  latitudes alpine is found at high altitudes

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Continental Glaciers

• continental glaciers are vast ice sheets which
  originate in high latitudes.
• cold temperatures allow snow to accumulate to
  great depths
• Antarctic and Greenland are the two major
  expanses of ice sheets on Earth today.

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Alpine Glaciers

• alpine glaciers are those that form at high
  altitudes where the environment is suitable to
  glacier formation
• flow outward from their zone of accumulation and
  erode the surface beneath
• created some of the most spectacular landscapes
  on Earth

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How glacier ice is formed
http//craton.geol.brocku.ca/faculty/rc/teaching/1
F90/glaciers/figure141.html
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• 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 (in other words,
  the snow becomes denser)
• after the first year it is called neve and it is
  about 50 pore space

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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 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

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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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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 flowage
• 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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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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Ice Ages

• Earth has gone through several ice ages
• 2 billion years ago
• 600 million years ago
• 250 million years ago
• 1 million years ago
• 20,000 years ago
• ice sheets covered almost all of Canada and parts
  of the U.S.A., Europe and South America during
  each glacial advance
• enormous volumes of water were frozen in these
  ice sheets.

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When does a glacial period begin?

• recurring long term cyclical changes in Earth's
  orbit around the sun and in the angle of Earths
  axis mean less solar radiation received in the
  Northern Hemisphere in the winter resulting in
  very cold winters and cool summers

http//www.canadiangeographic.ca/magazine/nd97/ima
ges/20000.jpg
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• cool summers in the northern hemisphere prevent
  the melting of winter snows
• accumulating snow and ice in turn reflect more of
  the sun's heat away from Earth's surface and
  Earth cools even more
• snow and ice accumulate in high latitudes and
  altitudes and flow outwards
• ice age is under way

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http//www.crystalinks.com/iceage2.jpg
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http//geolibertaire.org/image/p-b/neolithique/der
nieres_glaciation_1.jpg
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Advancing and Retreating

• during the last ice age the glaciers advanced and
  then retreated at least four times
• advance move forward
• retreat move back

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http//www.thecanadianencyclopedia.com/index.cfm?P
gNmTCEParamsA1ARTA0003271
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Current glaciation
http//pubs.usgs.gov/factsheet/fs133-99/worldmap.g
if
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http//courses.missouristate.edu/EMantei/creative/
glg110/glaciers.html