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Glaciers (I): mass balance and glacier motion

Glaciers (I): mass balance and glacier motion. Geog 1011 Landscape and Water Nov 28, 2005 Adina Racoviteanu. Glaciers (Part I). Glacier formation Glacier mass balance Types of glaciers Glacier flow Major surface features of ice Glacier fluctuations and climate (on Friday).

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Glaciers (I): mass balance and glacier motion

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  1. Glaciers (I): mass balance and glacier motion Geog 1011 Landscape and Water Nov 28, 2005 Adina Racoviteanu

  2. Glaciers (Part I) • Glacier formation • Glacier mass balance • Types of glaciers • Glacier flow • Major surface features of ice • Glacier fluctuations and climate (on Friday)

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

  4. 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

  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. Climatic conditions • cool temperatures in summer (average temperatures < O deg C) • high winter precipitation Moisture important!!! Eg: Siberia and parts of Antarctica: • low temperatures but • lack of adequate precipitation --> prevent glacier development

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

  11. 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

  12. Transformation of SNOW --> ICE • Rate of transformation dependent on temperature and accumulation rate • Rate with load • Rate with Temperature (for a given load) • temperature determines size of crystals and amount of snowfall

  13. The glacier story (cont’d): 2. glacier growth Accumulation: • snowfall • avalanches : e.g. Karakoram, Andes • wind 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. Glacier Mass Balance area where ice melts • area where ice accumulates Equilibrium line altitude (ELA) accumulation = ablation balance = 0

  19. Mass balance • NEGATIVE: glacier gets smaller • POSITIVE: glacier gets larger • ZERO MASS BALANCE: • no change in glacier size (mass,volume) • GLACIER STILL MOVING FORWARD!!!

  20. Where is the ELA?

  21. Where is the ELA?

  22. Classification of glaciers:thermodynamic 1) Warm glaciers • warm based • thawed from their bed • slide and flow

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

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

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

  26. Glacier movement Ice is solid but it flows! • When glacier reaches critical mass (>20m thick) • flow occurs

  27. Glaciers flow!! East Greenland

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

  29. Two types of glacier movement 1) PLASTIC DEFORMATION • COLD based glaciers 2) BASAL SLIDING • WARM based glacier Temperature main limiting factor as it dramatically alters the amount of water present!

  30. 1. Internal deformation Stress: Compaction (weight) • Ice > 60m thick • specific for cold-based glaciers (frozen to bed) velocity • Factors controlling rate of deformation: • depth of ice • slope Strain = amount of deformation

  31. 2.Basal sliding • needs melt water! • glacier slips over the rock surface • less friction Gravity main driving force, s = rgh*sina -water acts as lubricator -sliding What if the glacier encounters a bump????

  32. Steady-state flow rates 5-500m/a • Fastest flow in upper/central parts • Area of least friction Glacier flow

  33. Glacier travel:Major surface features 1) Crevasses: • deep, V-shaped structures found in the uppermost layer of the glacier. • form due to different velocities between center and edges of glacier • perpendicular to direction of flow

  34. Accumulation area is often heavily crevassed Direction of flow New Zealand

  35. 2)Bergschrund: crevasse that separates flowing ice from stagnant ice at the head of a glacier Glacier on Shorong Yul-lha, Nepal

  36. 3.Icefall: steep, fast-flowing section of glacier with cracked and jumbled surface Khumbu Ice fall, Everest

  37. 4) Ogives: alternate bands of light and dark ice on a glacier (winter) (summer)

  38. 5) Séracs: • towers of ice formed by • intersecting crevasses • rapid flow • steep slopes Glacier des Bossons, French Alps photo: MH

  39. 6) Penitentes: spiky columns of snow; formed in dry environments Nev. Coropuna, Peruvian Andes

  40. 7) Melt stream: on the glacier surface 8) Moulins water Very slushy and slippery!!

  41. Glacier hazards • Glacier surges • Glacier lake outburst floods • Ice avalanches • Falling ice

  42. Glacier surges Glacier surges = short-lived episodes involving a sudden increase in ice movement by at least one order of magnitude, sometimes two orders, compared to presurge, and post-surge behavior Glacier surge areas: · Alaska, and theYukonTerritory, Canada; · Svalbard; Iceland; Greenland; · the Russian High Arctic; · Asia (the Pamirs, theTien Shan and the Karakoram)

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

  44. Medial moraines (tear-drop shape)from past surges Bering glacier, Alaska

  45. 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.

  46. Himalayas: morraine-dammed lakes

  47. After the glacier lake outburst….

  48. A strange feature in the ice: Glacier mummies Otzi- 5,000 year old mummy found in Tyrolean Alps, Italy Glacier retreat revealed mummy 500-year old mummy found in Peruvian Andes

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