1. 16 - Glaciers as Landforms 2% of all water 88% of FW Covers Antarctica and Greenland avg 2.5 km thick Max 4 km thick During Pleistocene 20% of water on land Accumulation Accumulation and Ablation Unconfined Ice Sheet

2. Geomorphology of Alpine Glaciers http://www2.wwnorton.com/college/geo/egeo/animations/ch18.htm Equilibrium line ~snow line, maximum flow in x-sec. Glaciers much higher average surface gradient than streams Valley Glaciers

3. A Cirque Glacier

4. End of Glacier Debris Flow

5. Importance of glaciers Influence earth’s energy balance - albedoInfluence earth’s energy balance - albedo Major component of (fresh) water storage – affects sea levelMajor component of (fresh) water storage – affects sea level Important agent of landform evolutionImportant agent of landform evolution Center moves faster than margins. Note ogives, annual waves

6. Obstacles Upglacier, the movement of ice closes joints in the rock. Only abrasion occurs. Downglacier, over the crest of the bedrock, ice flow opens joints. Meltwater gets into cracks and freezes, enlarging cracks. Plucking removes rock.

7. Davidson Glacier near Haines, Alaska An Alpine glacier system Ledges (obstacles) beneath ice reflected by Crevasse Fields and Ice Pinnacles (Seracs) Accumulation zone extending, ablation zone and buried obstacle compressing Terminus

9. Ice Caps and Continental Ice Sheets Sentinal Range, Antarctica http://www.nmm.ac.uk/server/show/conWebDoc.1221 Antarctica is the broadest high place on Earth, the ice cap is up to 4km thick and covers the continent Antarctica is a desert, with only 15 cm (6 inches) of snowfall a year around the South Pole The lowest recorded temperature is -89.2 °C. There is no life in Antarctica except near the coast White, reflective, high latitude, positive feedback Nunatak

10. Nunatak: exposed rocky area not covered with ice or snow

11. Byrd Glacier, Antarctica, an outlet glacier

12. Zone of Accumulation Outlet Glaciers Ablation Ablation Vatnajokull http://pubs.usgs.gov/fs/2005/3056/

13. Formation of Glacier Ice Firn BTW: note leading edges thrust over terminal debris

14. Ice Deformation Accelerating slowing

15. Wet Glaciers Warm = wet-based Cold = dry-based ρ ice < ρ water, therefore Pressure increase on ice increases density to that of liquid water. Causes "melting point decrease“. Ice than would normally melt at 0 o C = 32 o F now melts at a cooler temp. High pressure melting point called PMP - pressure melting point –0.7°C/ km of ice above you “Warm” ice = thick, fast Moves mostly by basal sliding on wet base Pressure Melting Point

16. Cold, High Polar, Dry Based Base ice is frozen These glaciers do not slide, they only move by internal deformation Plucking

17. Intermediate (subpolar)

19. Temperate, Wet Bed Striations, transport by subice flows

22. Rapidly Flowing Glaciers

23. Observed Ice Core Temps Greenland –T bed < 0°C Antarctica –T bed ≈ 0°C

24. Pressure Melting and Regelation For ice near Pressure Melting Point: –Movement increases pressure, thus melting, on the up-ice side of an obstruction –Movement away from the obstruction releases pressure - causes freezing on the down-ice side – “regelation” melt melt

25. Effects of Pressure Melting High pressure is experienced on the up-ice side of an obstruction. Pressure melt results Water migrates around obstacle Regelation occurs in low pressure zone MELT REFREEZE = "Regelation"

26. Erosion by Plucking Melt then regelation mix loose bed material and refreezing ice at base – gets into rock cracks, expands w/ freeze and pushes: “plucking”

27. Abrasion Plucked material is available to wear away the bed – “abrasion”

28. Abrasion Features / chattermarks

29. Polish Typical of similar hardness (bed vs. tool) and fine load (~ sandpaper)

30. Glacial Abrasion in Bedrock Source: Tom Bean

31. Glacier Hydrology Liquid water flows on, within, and beneath glaciers

32. Subglacial Channels Eroded into bedrock Polar Glaciers –Pressure –Tools

33. Subglacial - Ice Caves Ice Cave Mendenhall Glacier, AK Photographer: John Bortniak, 1991 NOAA Corps Note Ice contact debris

34. To be continued outwash terminus