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Glaciers

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

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Glaciers

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  1. Glaciers Geog 3251 Mountain Geography summer 2006 Adina Racoviteanu

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

  3. 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

  4. What is a glacier? • Mass of moving glacial ice created by the accumulation of snow • glaciers always moving forward at terminus

  5. Arctic The Norwegian Arctic Archipelago of Svalbard is 60% covered by glaciers.

  6. Antarctica East Antarctic Ice Sheet Photo: MH

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

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

  9. Is this a glacier? No- Icebergs are NOT glaciers

  10. 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?

  11. 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

  12. 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 Air bubbles density > 860 kg/m3

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

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

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

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

  17. Calving Hubbard glacier, Alaska photo:Jürg Alean

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

  19. Warm glaciers Qori Kalis, Quelcaya Ice Cap, Peru

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

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

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

  23. Glaciers flow!! East Greenland

  24. Compression False-colour Landsat image Malaspina Glacier, Alaska (NASA, 31.8.2000).

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

  26. 1. Internal deformation Stress: Compaction (weight) • ALL glaciers move by deformation • Factors controlling rate • of deformation: • depth of ice • slope Strain = amount of deformation

  27. 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????

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

  29. Glacier movement summary 1. Temperature at base of glacier is key WARM glaciers: sliding + deformation COLD glaciers: deformation only strength 2. Gravity main driving force s = rgh*sina stress θ compression gravity

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

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

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

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

  34. 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)

  35. Variegated glacier, Alaska • velocities of 100m/day • dramatic increase in flow rate, 10-100 hundred times faster than its normal rate

  36. Himalayas: morraine-dammed lakes

  37. After the glacier lake outburst….

  38. 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.

  39. Questions? • Glaciers online • NSIDC: All about glaciers

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