Transcript GLACIERS AND THEIR EFFECTS

GLACIERS
AND
GLACIATION
II
Topics
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Glacial landforms
– Glacial sedimentation
– Permafrost
– Glacial lakes
Glaciations and global climate
Terminal moraine
Courtesy Gerald Osborn
Other Glacial Landforms
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Drumlins– Elongated hills of glacial till
– Point down-glacier
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Eskers
– Sinuous ridges of stratified till
– Form in tunnels under the ice sheet
– Some times 100km long or more
Drumlin field in Wisconsin
Permafrost
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Frozen ground
Found in Arctic
– North America
– Russia
Formed during last ice age
More than 1000 m deep in places
Global warming -> melting of permafrost
Distribution
of permafrost
in the
northern
hemisphere
Fig. 12.29
Lateral variations in
permafrost in Siberia
Fig. 12.30
Glacial Lakes
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Pluvial Lakes– Due to wetter climate
– Examples: Lake Bonneville, Death Valley
– Lake Bonneville flood into Snake River
Canyon
Proglacial Lakes
– In front of the glacial sheet
– Ice dammed lakes
– Examples: Great Lakes, Lake Missoula
Lake Bonneville14,000 yrs agoUtah
Lake Bonneville Flood
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The lake was up to 1000 feet deep
A ridge on the north side gave way
Peak flow = 33 million cubic feet/second
33 MCF would fill a tanker train 165 miles long
A raft would move at 75 mph on a wave 300 ft
high
Flood left behind giant ripples
Glacial ages
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Northern Europe & North America heavily
glaciated
– Peak of glaciation 18,000 years ago
– Ended about 10,000
– We are still in the cold part of the climate cycle
Episodic climate changes
At peak glaciation
– Average global temperature only 5 degrees
colder
Effects of Past Glaciation
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Glacial ages
Direct effects in North America
– Scoured much of Canada
– Cut Great Lakes
– Deposited till & flattened Midwest
– Extensive alpine glaciation in mountains
– Allowed Natives to walk from Siberia
Effects of Glacial Ages
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Indirect effects
– Pluvial lakes
– Lowering of sea level
»
–
Fiord
Crustal rebound
Causes for glaciation
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Astronomical
Variations in solar radiation
Atmospheric changes
Tectonic causes
Causes for glaciation
Astronomical (Milankovitch cycles)
– Eccentricity of orbit (100,000 yr cycle)
– Wobble of rotation axis (41,000 yr cycle)
– Precession of equinox (23,000 yr cycle)
 Variations in solar radiation
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Variations of Earth’s orbit
Tilt of Earth’s Rotation Axis
Wobble of the rotation axis: Precession
Fig. B12.5
Causes for glaciation
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Atmospheric changes
– CO2 (Greenhouse effect)
– Volcanic ash
Tectonic causes
– Continents near the poles
– Oceanic circulation patterns
Gas Concentrations in Deep ice
core-Antartica
Fig. 12.34
Causes for glaciation
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Tectonic causes
– Continents near the poles
– Oceanic circulation patterns
Paleozoic (300 Ma) Glaciation
What if the glaciers melt?
Retreating Rhone Glacier
S. C. Porter