glaciers and glaciation. glacier a body of ice formed on land recrystallization of snow=> firn...
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GLACIERSAND
GLACIATION
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GLACIER
• A body of ice
• Formed on land
• Recrystallization of snow=> Firn => Ice
• Evidence of movement
• Alpine (valley) glaciation
• Continental glaciation
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Ice Ages
• Northern Europe & North America heavily glaciated– Pleistocene 1.8 million years BP to 10,000 ybp
• 4 episodes
– Peak of glaciation (Wisconsin) 18,000 years ago
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Glaciers-Where they are
• Develop where all of annual snow doesn’t melt away in warm seasons: Accumulation rate rate exceeds ablation rate– Polar regions– Heavy winter snowfall– High elevations– 85% in Antarctica– 10% in Greenland
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Types of Glaciers
• Valley or Alpine glacier
• Ice sheet– Continental Glaciers
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Formation and Growth of Glaciers
• Snow to firn to glacier ice• Wastage (or ablation)
– Melting, evaporation, – Calving into icebergs
• Glacial Budgets– Negative budget- Receding glacier– Positive budget- Advancing glacier– Zone of accumulation; Zone of wastage
• Snow line- divides the zones
– Terminus- movement reflects budget
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GLACIERS
• Wastage of glaciers (“shrinkage”)– Melting
• more melting at lower elevations
– Evaporation– Calving into Icebergs
• where a glacier flows onto a sea
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GLACIERS
• Advancing vs. Receding Glaciers• Zone of accumulation
– Where some snow remains after the melt season
• Zone of Wastage– Where all snow & some glacier melt
• Advancing glacier-– positive budget - terminus moves forward
• Receding glacier– negative budget - terminus retreats
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Movement of Glaciers
• Valley Glaciers– Gravity driving force– Sliding along its base -basal sliding– Internal flowage- plastic flow– Rigid zone
• Crevasses may form here
• Ice sheets– Move downward & outward from central high
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Glacial Erosion• Under glacier
– Abrasion & plucking– Bedrock polished & striated– Rock flour washes out of glacier– Polishing and rounding
• “Sheep Rocks”
– Striations- scratches & grooves on rock
• Above glacier– Frost wedging takes place– Erosion by glaciers steepens slopes
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Erosional Landscapes Associated with Alpine Glaciation
• Glacial valleys– U-shaped valleys– Hanging valleys– Truncated spurs
• Triangular facets
– Rock -basin lakes (tarns)– Rounded knobs- rouche moutonnees
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Erosional Landscapes Associated with Alpine Glaciation
• Cirque- at head of valley glacier– Rock steps
• Rock basin lakes
• Horn
• Arete- sharp ridge
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Erosional Landscapes Associated with Continental Glaciation
• Grooved and striated bedrock– Grooves may be channels
• Rounded hills & mountains
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Glacial Deposition• Till
– Unsorted debris (Boulders to Clay)
• Erratic
• Moraine- body of till– Lateral Moraine– Medial Moraine- where tributaries join– End moraine-
• Terminal
• Recessional
– Ground moraine– Drumlin
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Glacial Deposition
• Outwash– Stream-deposited sediment
• sorted
– Braided streams typical– Esker– Kettle
• Glacial lakes– Varves
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Effects of Past Glaciation
• Glacial ages
• Direct effects in North America– Scoured much of Canada– Cut Great Lakes– Deposited till & flattened Midwest– Extensive alpine glaciation in mountains
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Effects of Glacial Ages• Indirect effects
– Pluvial lakes– Lowering of sea level
• Fiord
– Crustal rebound
• Evidence for older glaciation– Tillite– Late Paleozoic glaciation
• Evidence for a supercontinent
– Precambrian glaciation
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