Chapter 12 Glaciers and Glaciation

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Chapter 12Glaciers and Glaciation
Photo credit G. Mattioli
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Glaciers and Glaciation Topics

• Glaciers
• Global Distribution
• Mechanisms of Formation
• How and Why They Move
• The Theory of Glacial Ages - Louis Agassiz, 1837
• Profound Changes in Global Climate
• Related to Changes in Orbital Characteristics
• Changes in Global Sea Level
• Post-glacial Uplift

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Modern Glacier Distribution

• Mostly limited to Polar Regions
• Northern Hemisphere Sea Ice Pack is seasonal and
  ephemeral
• Greenland Ice Sheet is permanent (10)
• Antarctic Ice Sheet is permanent (85)
• Remaing Alpine glaciers amount to only 5
• Most of the Earths freshwater is bound up in
  Antarctic Ice Sheet
• 2 of total global water budget

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Northern Hemisphere Polar Ice
NASA/CSA Resources - Composite radar image draped
on visible image
Image source NASA Jet Propulsion Lab
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Arctic Sea Ice Growth
Baufort Sea, north of the Alaskan coast
Images taken 9 days apart. RadarSAT scenes are 60
x 80 miles. Brighter features are older ice and
darker features are newly formed ice.
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Glacial Characteristics

• Distribution of Glaciers
• Types of Glaciers
• Continental Ice Sheets
• Alpine
• Formation and Growth of Glaciers
• Movement of Valley Glaciers
• Movement of Ice Sheets

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Modern Valley Glacier
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Yosemite Valley
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Valley Glacier Zones
Zone of ablation
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Valley Glacier Formation - Seasonal Variation
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Receding South Cascade Glacier
1957
1980
Loss of 18.7 M m3 of ice - Due to global warming?
Photo credits U.S. Geological Survey
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Snow to Ice
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Polycrystalline Ice in Polarized Light
Individual Ice Crystals
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LANDSAT Composite Antarctica
Highest Point
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Continental Ice Sheet Development
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South Pole
Pole erected 1956 - Movement of Ice Sheet has
displaced it from current geographic south pole
several km away!
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Icebergs
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Meteorite Accumulation
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Glacial Movement - Mechanisms
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Glacier Movement Animation
Note that velocity is NOT constant with depth
nor is the mechanism that allows the ice to move!
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Glacial Crevasses
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Crevasse Formation Animation
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Glacial Erosion

• Erosional Landscapes Associated with Alpine
  Glaciation
• Erosional Landscapes Associated with Continental
  Glaciation  

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Glacial Erosion Striations
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Alpine Glacial Landforms
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Alpine Glacial Features - Grand Teton
Horn
U-shaped Valley
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Arete - Mt. Logan, Yukon Territory
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Hanging Rivers - U shaped Valley
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Bedrock Fractures and Glacial Erosion
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Glacial Cirque
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Crevasse Development
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Striated Bedrock
South Australian Paleozoic Glaciation
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Roche Moutonée with Striae
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Glacially Scoured Terrain, Canadian Arctic
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Glacial Deposition

• Moraines
• Outwash
• Glacial Lakes and Varves 

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Alpine Moraines and Till
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Moraine Types
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Lateral and Medial Moraines
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Glacial Valley Landforms
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Glacial Outwash Features
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Outwash Features
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Varved Sediments
Seasonal Deposition Light color silt
(summer) Dark color clay (winter)
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Effects of Past Glaciation - 1

• The Glacial Ages
• Occur repeatedly through geologic time
• Most recent period initiated 3 Ma ago and peaked
  18 Ka ago
• Antarctica has been glaciated for 20 Ma
• Direct Effects of Past Glaciation in North
  America
• Great Lakes, Finger Lakes
• Terminal Moraines, Drumlins
• Glacial Erratics - odd rocks from northern craton

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Drumlin and Glacial Erratic
Flow Direction
Teardrop-shaped
Images from http//mail.rochester.edu/kl001i/lan
derk2.html
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Effects of Past Glaciation - 2

• Indirect Effects of Past Glaciation
• Pluvial Lakes
• Lower Sea Level - Submerged Canyons on the Shelf
• Coastal Fiords
• Crustal Rebound
• Evidence for Older Glaciation
• Tillites (lithified glacial till)
• Evidence for Continental Drift and Plate
  Tectonics
• Snowball Earth hypothesis - cold, ancient Earth
  due to weaker sun, lower CO2

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Pleistocene Glaciation
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Maximum Extent of Pleistocene Glaciers
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Finger Lakes - Western NY
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Lake Missoula, MT
Giant ripples of gravel - formed when glacial
lake emptied
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Inland Passage - Alaska
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Mechanisms for Past Glacial Periods

• Pleistocene glacial and interglacial episodes are
  correlated with variations in the Earths orbit
  at 21 ka, 41 ka, and 100 ka. Discovered by M.
  Milankovitch in 1921.
• General absence of glacial periods in the past is
  NOT explained by Milankovitch cycles.
• Other mechanisms
• Changes in CO2 content in the atmosphere (large
  volcanic eruptions can lower global temperature).
• Movement of the continental landmasses by
  tectonics.
• Changes in oceanic circulation as a result of
  both atmospheric and tectonic processes.

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Milankovitch Cycles in Earths Orbit
Image Source Scott Rutherford
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Snowball Earth Carbon Cycle
Figure from Hoffman and Schrag (1999)