Glaciers and

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Glaciers and Ice
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Glacial Systems

• An open system of flowing ice
• Water input as snow
• Transformed into ice
• Ice flows under pressure
• Water leaves by evaporation and melting

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Glacial Ice

• Glaciers maintain a balance of ice
• Zone of accumulation - net gain in ice
• Zone of ablation - net loss of ice
• Snow line - boundary between zones

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Accumulation i.e. snowline Ablation
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Types of Glaciers

• Glaciers divided into 2 subsystems
• Valley glaciers
• Ice streams flowing from mountain areas down
  valley
• Continental Glaciers
• Large-scale Ice Sheets

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Ice Flow

• Glaciers move by slow deformation of the ice due
  to increase in pressure from the overlying ice
• Shifting and rotation of ice crystals
• Pressure melting lubricates ice
• Displacement along slip planes

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• Movement of is dependent on snow accumulation and
  slope
• Accumulation is greatest at glacier head
• Gravity pulls ice downward outward
• Flows parallel to surface through ablation zone

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• Movement is not uniform
• Velocity increases from head to snow line
• Velocity decreases after snow line

• Ice is brittle ductile
• Differential flow velocity creates tensional
  stress
• Crevasses form as a result of differential flow

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Glacial Equilibrium

• Water (ice) moves through the open glacial system
• At EQ, input output - mass balance
• If input gt output, glacier expands
• If input lt output, glacier shrinks

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Erosion

• Powerful agents of erosion
• Up to 0.35 mm/yr
• Ice wedging tends to smooth surface
• Plucking pulls up loose fragments
• Ground-up rock
• abrades surface

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Valley/Alpine Glacier Systems

• Cirque glaciers
• A protected bowl shaped depression
• Bounded by steep cliffs, headwall
• Open on the downslope side

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• Valley glaciers
• Growing cirque spreads down a valley
• Glaciers may fill long mountain valleys
• Glacier pluck rock debris forming moraines

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• Glaciers produce unique geomorphic features
• Arete- A sharp crested ridge bounded by 2 cirques
• Horn - A sharp peak bounded by 3 or more cirques
• Hanging valleys - characteristic U shape valley
  of a smaller glacier

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Continental Glacier Systems

• Most important glacial system
• Modify pre-existing landforms
• Cause crustal subsidence
• Modify drainage systems
• Important component of the hydrologic system
  climate

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• Ice sheets
• Continent-sized ice masses
• Ice sheets include 95 of all glacier ice
• Antarctica Greenland
• Glacial ice accounts for 2.14 of all water on
  Earth

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• Ice caps
• Covers large area of mountains or high altitude
  plains
• Ice shows outward radial flow
• Ice shelves
• Tabular ice bodies resting on the ocean floor

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• Geomorphic features indicate past glacial
  coverage
• Till - debris that accumulates beneath and at
  glacier margins
• Drumlins - streamlined hills
• Ground moraine - deposited beneath ice
• Eskers - melt water stream deposits

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