glaciers chapter 17. why glaciers? 10% of earth covered by ice 85% antarctica 11% greenland 4%...
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Glaciers
Chapter 17
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Why glaciers?
10% of earth covered by ice
85% Antarctica11% Greenland4% elsewhere
Glaciers store about 75% of the world's freshwater
•Distribution: found at variouslatitudes and climates
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What is a glacier?
• Mass of moving glacial ice created by the accumulation of snow
• glaciers always moving forward at terminus
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The Norwegian Arctic Archipelago of
Svalbard is 60% covered by glaciers.
Arctic
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East Antarctic Ice Sheet
Antarctica
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Nev. Piramide, Cordillera Blanca, Peruphoto: Michael Hambrey
Tropical
glaciers
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Mid-latitude glaciers: Nepal Himalaya
Photo: A. Racoviteanu
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Glacier birth
• accumulation
• snow metamorphism
• compression
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Air bubbles
Glacial Ice formation
• SNOW: seasonal snow void spaces
• FIRN (névé): snow that has lasted more than one year less void space density ~ 550 kg/m3
• ICE: compacted, air pores not connecteddensity > 860 kg/m3
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Mass Balance
• Accumulation
• Ablation
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Avalanche-fed glaciers
Nev. Chacraraju, Cordillera Blanca, Peru
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Melting
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Calving
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Mass balance
• area where ice accumulates
area where ice melts
Equilibrium line altitude (ELA) accumulation = ablationbalance = 0
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Austin Post photoSouth Cascade Glacier, Sept 20, 1966From NSIDC
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Exit Glacier, Alaska
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Bar graph showing winter, summer and net balance at Storbreen during 1949-2004.
www.nve.no
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Movement of ICE
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1. Internal deformation
• ALL glaciers moveby deformation
Factors controlling rate of deformation:
•depth of ice•slope
Stress: Compaction (weight)
Strain = amount of deformation
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2. Basal sliding
• needs liquid water!
• Warm-based glaciers only
• glacier slips over the rock surface
• less friction -water acts as lubricator-sliding
What if the glacier encounters a bump????
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Regelation requires pressure-melting, transfer of water around the bump, and transfer of heat through it
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Glacier movement summary
1. Temperature at base of glacier is key
WARM glaciers: sliding + deformationCOLD glaciers: deformation only
2. Gravity main driving force
gh*sin stress
strength
gravity
θ
compression
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