Glaciers and the Great Ice Ages

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Glaciers and the Great Ice Ages
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Pleistocene Epochthe Great Ice Ages

• 2.0 Ma to 10,000 years ago
• Four (or more) distinct episodes expansion and
  melting of ice sheets (continental glaciers)

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Why did the climate change so drastically and
repeadedly?

• Climate change and variations in Earths orbit
• Eccentricity elliptical to nearly circular
  cycles
• Obliquity cyclic changes in tilt of axis
• Precession cyclic change inwobble of the axis
• Variations affect amount and distribution of
  solar energy received by Earth

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How does a glacier form?

• Cold climate is necessary
• Annual snow accumulation is greater than annual
  rate of melting
• Snow builds up over time
• Snow recrystallizes to ice

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Glacial Flow

• Ice begins to flow (plastic deformation) under
  the influence of gravity
• Glacier mass of flowing ice

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• Glaciers are dynamic
• Flow is constant
• Some parts of glacier are melting
• Rate of accumulation vs. rate of melting
  determines if glacier will advance or if end of
  glacier will melt back (glaciers never flow
  backwards)

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Glaciers and Landscapes

• Flowing ice picks up sediment, soil, etc.
• Breaks loose pieces of bedrock
• Modifies landscape by erosion and deposition

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Erosion by Glaciers

• Striations scratchmarks made as ice drags
  rocks across bedrock

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Erosion by Glaciers

• Modifies V shaped river valleys to a U shape

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Deposition by Glaciers

• Erratics pieces of exotic rock left by
  glacier
• Till unsorted, unstratified sediments dumped by
  ice
• Outwash sorted and stratified sand and gravel
  deposited by meltwater

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Deposition by glaciers

• Lacustrine sediments
• Lakes form between melting edge of ice and
  obstructions (often deposits of till)
• Fine silt and clay settle to the bottom in calm
  water
• Clay may be used in pottery and brick making
• If lakes drain or fill with sediment
• bogs and swamps ecologically important wetlands
• Water-logged lacustrine sediments may cause
  tilting and sinking of buildings constructed on
  them

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Glaciers and Landforms

• Characteristic landforms