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Glaciers
Chapter 17
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
What is a glacier?
• Mass of moving glacial ice created by the accumulation of snow
• glaciers always moving forward at terminus
The Norwegian Arctic Archipelago of
Svalbard is 60% covered by glaciers.
Arctic
East Antarctic Ice Sheet
Antarctica
Nev. Piramide, Cordillera Blanca, Peruphoto: Michael Hambrey
Tropical
glaciers
Mid-latitude glaciers: Nepal Himalaya
Photo: A. Racoviteanu
Glacier birth
• accumulation
• snow metamorphism
• compression
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
Mass Balance
• Accumulation
• Ablation
Avalanche-fed glaciers
Nev. Chacraraju, Cordillera Blanca, Peru
Melting
Calving
Mass balance
• area where ice accumulates
area where ice melts
Equilibrium line altitude (ELA) accumulation = ablationbalance = 0
Austin Post photoSouth Cascade Glacier, Sept 20, 1966From NSIDC
Exit Glacier, Alaska
Bar graph showing winter, summer and net balance at Storbreen during 1949-2004.
www.nve.no
Movement of ICE
1. Internal deformation
• ALL glaciers moveby deformation
Factors controlling rate of deformation:
•depth of ice•slope
Stress: Compaction (weight)
Strain = amount of deformation
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????
Regelation requires pressure-melting, transfer of water around the bump, and transfer of heat through it
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
