Glaciers

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• Glaciers Ice Ages

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Davidson Glacier near Haines, Alaska
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Glaciers

• Glacier a large, long-lasting mass of ice,
  formed on land that moves under the influence of
  gravity and its own weight
• Glaciers form by accumulation and compaction of
  snow
• Packed snow becomes firm
• Then refreezes to ice

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Formation of Glacial Ice from Snow
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Types Of Glaciers

• Valley Glaciers found in mountain regions
• Continental Glaciers exists where a large part
  of a continent is covered by glacial ice - cover
  vast areas

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Types of Glaciers
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Types of Glaciers Valley Glacier
Mount Edith Cavell, Jasper National Park, Canada
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Types of Glaciers Valley Glacier
Tongas National Forest, Alaska
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Types of Glaciers Icecap and Continental
Sentinal Range, Antarctica
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More on Glaciers

• Gain snow in zone of accumulation
• Lose ice in zone of ablation

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A Glaciers Budget
Year round Snow
Summer Rain
Note that a glacier is a river. Even if the
terminus doesnt advance, still flows
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Iceberg Calving Hubbard Glacier, Wrangell-St.
Elias National Park, Alaska
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Erosion by Glaciers

• Abrasion
• Rocks embedded in glaciers base make linear
  scratches and grooves in bedrock
• Plucking
• Glacier breaks off and removes large blocks of
  rock

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Glacial Abrasion in Bedrock
Source Tom Bean
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Glacial Erosion
Yosemite NP, California
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Landforms created by Glaciers

• Horn
• Cirque
• U-shaped valley
• Kettle lake
• Fiord
• Moraine

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Alpine Glacial Erosion
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Valley Glacial Erosion
Origin of Hanging Valley
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Yosemite Falls
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Valley Glaciers

• Erode a large quantity of bedrock and sediment
• Convert V-shaped stream valleys into U-shaped
  glacial valleys.

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U-Shaped Valley in Tracy Wilderness, Southeastern
Alaska
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Seawater Flooded U-Shaped Valleys Fjords
Bela Bela Fjord, BC
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Erosion by Continental Glaciation

• Erosional Landforms much larger in scale than
  alpine glaciers
• Huge U-shaped troughs, including
• Finger Lakes, Great Lakes, Puget Sound,
• and Loch Ness were all once valleys
• excavated by glaciers

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Erosion of Preglacial Lowlands (Finger Lakes)
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Erosion of Preglacial Lowlands (Great Lakes of
North America)
Source U.S. Dept. of Interior, USGS Eros Date
Center
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Glacial Deposits or Drift

• Glacial Till unsorted, unstratified sediments
  deposited by melting ice.
• May contain glacial erratics
• Often accumulate at glaciers terminus as a
  Moraine hills of sediment left by a glaciers
  retreat.

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Advance Retreat Moraines
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Large Granite Erratics
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Medial Moraines Kennicott Glacier
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Effects of Glaciation

• Change Climate increased precipitation
• Drop in sea-level alter coastlines
• Form continent-wide Dams
• Divert streams Ohio and Missouri rivers

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Lowered Sea-level - Landbridge
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Lowered Sea-level exposed continental shelf
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Giant Ripples of the Missoula Flooding
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Causes of Ice Ages

• Plate Tectonics
• Moves Continents to Poles
• Raises mountains above snowline
• Orbit Distances, Axis Tilt and Wobble
• Moderates solar radiation past 65 N
• Croll-Milankovitch Cycles 100,000 years
• Low summertime radiation causes glaciers to
  expand

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Glacier Distribution 20,000 ya
Approximate Maximum
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Milankovitch Cycles
100,000 years
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41,000 years
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Earths Past Ice Ages

• PreCambrian Glaciation
• 750 mya ice flowed from poles to tropics
• Late Pennsylvanian Permian Glaciation
• covered South Africa, South America, India,
  Australia
• Pleistocene Glaciation
• most recent, ended about 10,000 years ago

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Pleistocene Glaciation

• started 1.6 mya -30 advances and retreats
• Latest retreat ended 10,000 years ago
• Little Ice Age occurred 700 to 150 years ago,
  paralyzed Europe
• Next glaciation period - ???

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Sustained warming since 1850
Athabaska Glacier, Columbia Icefield, W. Canada
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End of Glaciers