Glaciers (Part I)

1. Glaciers (Part I) • What is a glacier? • Where are glaciers found? • What is climate effect on glaciers?

2. 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

3. Typical glacier system in Cordillera Blanca, Peru

4. Glacier landscape in Nepal Himalayas

6. Shorong Yul-lha glacier, Nepal Himalayas

7. How are glaciers formed? • where average temperatures < O deg C. • Snow accumulates and compressed by weight of layers • buried layers slowly form a thickened mass of ice • snow grains squashed together-- snow metamorphosis

8. Glacial Ice formation • SNOW: seasonal snow void spaces • FIRN (névé): snow that has lasted more than one year less void space • ICE: compacted, air pores not connected Air bubbles density > 860 kg/m3

9. 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

10. Thermodynamic classification of glaciers • “Cold” glaciers: • frozen to the rock of their beds • ice below pressure melting point • remain well frozen; melting only at surface • “Warm” glaciers: • warm based • thawed from their bed • slide and flow

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

12. How does ice move? slower faster F slower

13. Two ways of glacier movement • PLASTIC DEFORMATION • BASAL SLIDING Gravity main driving force, s = rgh*sina

14. 1. Internal deformation Compaction weight • Ice > 60m thick • specific for cold-based glaciers (frozen to bed) velocity Pressure melting point • Factors controlling rate of deformation: • depth of ice • temperature • slope

15. 2.Basal sliding • only “warm-based” glaciers • glacier slips over the rock surface • H2O as lubricator • less friction • velocities: 0-300m/day -water -sliding

16. Glacier surge • velocities of 100m/day • dramatic increase in flow rate, 10-100 hundred times faster than its normal rate

17. Structures within glacial ice • Crevasses: • cracks in the ice due to different velocities between center and edges of glacier • formed perpendicular to direction of flow

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

19. Crevasses

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

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

22. Geographical and Climatic conditions • high snowfall in winter • cool temperatures in summer • Moisture important!!! • Eg: Siberia and parts of Antarctica: low temperatures meet glacier growth requirements, but lack of adequate precipitation prevents glacier development

23. Glacier distribution & importance • 10% of earth covered by ice • 85% Antarctica • 11% Greenland • 4% elsewhere • Glaciers store about 75% of the world's freshwater

24. Glacier Mass Balance • (Net)Accumulation zone = area where ice accumulates • (Net) Ablation zone= area where glacial ice melts • Equilibrium line where accumulation=ablation balance = 0 (at equilibrium)

26. Where is the ELA?

27. Where is the ELA?

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

29. ELA and climate • Cooling -- ELA lower • Warming -- ELA higher • Polar glaciers: ELA lower • Tropical glaciers: ELA higher

30. How do glaciers reflect climate change? • Climate change: • changes in temperature • changes in amount of moisture • Glaciers sensitive to temperature fluctuations • climate change can cause glaciers to melt • but the relationship is not straightforward, • eg. Antarctica:climate change-->warmer-->more evaporation from ocean ->more water vapor -> more snowfall!

31. Ice ages • Ice ages return every 100,000 years • approx. 20 ice ages • Pleistocene = most recent ice age, that started about 2 million years ago and ended ~10,000 yrs ago • 4 major advances of ice, most recent ones: • Laurentide: ended 20,000 yrs ago • Wisconsin: ended 100,000 yrs ago • Presently we are in an interglacial period

33. Causes of ice ages? Milankovic cycles long term variations in Earth’s orbit around the Sun:

34. Glacial ages • During the last Ice Age, glaciers covered 32% of the total land area. • Little Ice Age: • 17th century - late 19th century • consistently cool temperatures • significant glacier advances.

35. Earth’s climate record

36. Glaciers sensitive to climate changes: a few facts • strong warming over the last 50-200 yrs • increasing CO2 levels • Alpine glaciers have been experiencing rapid retreat • Ice cap on Mt. Kilimanjaro has been decreasing by 82% in the last 88 years • Glaciers in the Alps decreased by 50% in volume

37. Ice-albedo (positive) feedback Global warming + + Glacial melt More energy absorbed + Decrease in surface of ice + + Decrease in albedo

38. Climatic responses- scenarios • winter temperature: • less, not more, snow • polar areas get little precip. (cold air) • if summer ablation same -- glacier retreats • summer temperature: • more cloud cover • less summer ablation • if winter accumulation same -- glacier grows

39. Climatic response (cont’d) • winter precipitation (snowfall) • if no change in temperature • some snow survives over summer • glacier advances • temperature crucial factor-

41. Glacier response -summary • Alpine glaciers and N.Hem. Ice caps expected to retreat under global warming scenario • NOTE: Antarctica expected to grow due to possible increase in humidity

42. Monitoring glaciers • Field measurements • Aerial photography • Satellite images

43. Radar measurements - ice thickness

44. Aster image, Patagonia, Chile

46. Indian Himalayas: • Glacier ablation at • Gangotri, source of • the holy Ganges • glacier terminus retreated by • 3km ASTER Image courtesy of: NASA EROS Data Center, Sept. 9, 2001

47. Climate reconstructions • Ice core drilling Drilling tent on the summit of Cerro Tapado, Chile

49. Ice Core drilling, Coropuna, 2003

50. Having fun at high altitide... ..trying to get the generator to work