Transcript GLACIERS AND THEIR EFFECTS

GLACIERS
AND
GLACIATION
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Topics
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Intro
Glaciers and the Hydrologic cycle
Types
Movement
Glacial landforms
– Glacial erosion
– Glacial sedimentation
– Glacial lakes
Glaciations and global climate
GLACIER
A large body of moving ice
 Formed on land
 Recrystallization of snow
 Types:
– Alpine (valley) glaciers
– Continental glaciers
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Winter Sea Ice- Beaufort Sea
Sea IceBering Sea
Timble Glacier, Alaska
Valley Glaciers in
Denali National Park
Courtesy USGS
Hydrologic Cycle - 2% of water is Ice
What if the glaciers melt?
Glaciers-Where they are
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Develop where all of annual snow doesn’t melt
away in summer
– Polar regions
– Heavy winter snowfall
– High elevations
– 85% in Antarctica
– 10% in Greenland
Types of Glaciers
Valley glacier
 Continental Glaciers:
– Ice sheets (big)
– Ice cap (small)
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Greenland Ice
Sheet:
contours indicate
elevation of ice
sheet above sea level
Fig. 12.5
Ross Ice Shelf, Antartica
Formation and Growth of
Glaciers
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Metamorphism of Snow
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Glacial Budgets
– Zone of accumulation
– Zone of wastage
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Snow line- divides the zones
Negative budget- Receding glacier
Positive budget- Advancing glacier
Terminus- movement reflects budget
GLACIERS
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Wastage of glaciers (“shrinkage”)
– Melting
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more melting at lower elevations
Evaporation
Calving into Icebergs
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where a glacier flows onto a sea
Movement of Glaciers
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Valley Glaciers
– Gravity driving force
– Sliding along its base -basal sliding
– Internal flowage- plastic flow
– Rigid zone
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Crevasses may form here
Ice sheets
– Move downward & outward from central high
Glacial Erosion
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Under glacier
– Abrasion & plucking
– Bedrock polished & striated
– Rock flour washes out of glacier
– Polishing and rounding
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Striations- scratches & grooves on rock
Above glacier
– Frost wedging takes place
– Erosion by glaciers steepens slopes
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“Sheep Rocks”
Erosional Landscapes Associated
with Alpine Glaciation
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Glacial valleys
– U-shaped valleys
– Hanging valleys
– Truncated spurs
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Triangular facets
Rock -basin lakes (tarns)
Rounded knobs- rouche moutonnees
Erosional Landscapes Associated
with Alpine Glaciation
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Cirque- at head of valley glacier
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Rock steps
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Rock basin lakes
Horn
 Arete- sharp ridge
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Erosional Landscapes Associated
with Continental Glaciation
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Grooved and striated bedrock
– Grooves may be channels
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Rounded hills & mountains
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Glacial Deposition
Till
– Unsorted debris
Erratic
Moraine- body of till
– Lateral Moraine
– Medial Moraine- where tributaries join
– End moraine»
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Terminal
Recessional
Erratic-Alberta, Canada
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
Glacial Deposition
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Outwash
– Stream-deposited sediment
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Braided streams typical
– Esker
– Kettle
Glacial lakes
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sorted
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 in 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
Effects of Glacial Ages
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Indirect effects
– Pluvial lakes
– Lowering of sea level
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Fiord
Crustal rebound
Evidence for older glaciation
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Tillite
Late Paleozoic glaciation
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Evidence for a supercontinent
Precambrian glaciation
Causes for glaciation
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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
Atmospheric changes
– CO2 (Greenhouse)
– Volcanic ash
Tectonic causes
– Continents near the poles
– Oceanic circulation patterns