Glaciers Geog 3251 Mountain Geography summer 2006 Adina Racoviteanu.

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Presentation transcript:

Glaciers Geog 3251 Mountain Geography summer 2006 Adina Racoviteanu

Glaciers 1. Glacier formation, type and motion 2. Glacial landforms 3. Glacier-related hazards 4. Glaciers and climate (Friday & Monday)

Why glaciers? 10% of earth covered by ice –85% Antarctica –11% Greenland –4% elsewhere Glaciers store about 75% of the world's freshwater Distribution: found at various latitudes 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 Photo: MH

Nev. Piramide, Cordillera Blanca, Peru photo: Michael Hambrey Tropical glaciers

Mid-latitude glaciers: Nepal Himalaya Photo: A. Racoviteanu

Is this a glacier? No- Icebergs are NOT glaciers

What climatic conditions are needed for glaciers to form? cool summer temperatures in (< 0 deg. C) high winter precipitation Why don’t we have glaciers in Siberia or parts of Antarctica?

The glacier story: 1.glacier birth accumulation of snow compression of snow by weight of layers snow metamorphism: snow grains squashed together--> conversion to ice

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 connected density > 860 kg/m 3

The glacier story: 2. glacier growth Accumulation: snowfall avalanches : e.g. Karakoram, Andes wind re-deposition superimposed ice (rain freezing)

Avalanche-fed glaciers Nev. Chacraraju, Cordillera Blanca, Peru

Wind (re)deposition Nev. Huascaran, Cordillera Blanca, Peru photo:Jürg Alean

The glacier story (cont’d): 3. glacier decay Ablation: melting evaporation/sublimation (only cold arid areas) calving wind erosion

Calving Hubbard glacier, Alaska photo:Jürg Alean

Thermodynamic classification of glaciers: warm based thawed from their bed 1) Warm glaciers

Qori Kalis, Quelcaya Ice Cap, Peru Warm glaciers

2) “Cold” glaciers –frozen to their beds –ice below pressure melting point –remain well frozen; melting only at surface

Cold glaciers: Antarctica Hughes Glacier, Dry Valley, Antarctica photo: MH

Glacier movement When glacier gets >20m thick, flow occurs has to do with behavior of ice under pressure Ice is solid but it flows!

Glaciers flow!! East Greenland

False-colour Landsat image Malaspina Glacier, Alaska (NASA, ). Compression

Two types of glacier movement 1) PLASTIC DEFORMATION 2) BASAL SLIDING

1. Internal deformation ALL glaciers move by 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????

Glacier flow Steady-state flow rates 5-500m/a Fastest flow in upper/central parts ( less friction)

Glacier movement summary 1. Temperature at base of glacier is key WARM glaciers: sliding + deformation COLD glaciers: deformation only 2. Gravity main driving force  gh*  sin  stress strength gravity θ compression

Benefits of glaciers provide a reliable water supply for hydro-electric power generation & agriculture Cordillera Blanca, Peru

Canals Agricultural terraces Technological advances of the Incas Agricultural terraces Inca roads and trails Architecture

Benefits of glaciers recreation (climbing) Scenic value Pastoruri, Peru -major tourist attraction

Glacier hazards Glacier surges Glacier lake outburst floods (GLOF) Ice avalanches Falling ice

Glacier surges Glacier surges = short-lived episodes involving a sudden increase in ice movement by at least one order of magnitude Glacier surge areas:  Alaska, and theYukon Territory, Canada;  Svalbard; Iceland; Greenland;  the Russian High Arctic;  Asia (the Pamirs, theTien Shan and the Karakoram)

Variegated glacier, Alaska velocities of 100m/day dramatic increase in flow rate, hundred times faster than its normal rate

Himalayas: morraine-dammed lakes

After the glacier lake outburst….

Ice avalanches: May 30, 1970 Peru disaster A large mass of ice and rock slid from a vertical face on Nevado Huascaran Debris reached a velocity of 280 km/hr Buried 2 towns death toll: 20,000.

Questions? Glaciers online NSIDC: All about glaciers NSIDC: All about glaciers