Glacial Processes and Landforms

1. Glacial Processes and Landforms

2. Glacial Processes and Landforms Glaciers’ ability to erode soil and rock, transport sediment, and deposit sediment influenced more than 50 million square kilometers of land surface geomorphically during the last glacial period

3. Rivers of Ice Figure 17.1

4. Vatnajökull Ice Cap Figure 17.5

5. Patagonian Ice Field Figure 17.5

6. Greenland’s East Coast Figure 17.6

7. Glacial Processes:Growth of Glaciers • Formation of Glacial Ice • Begins as snow(density = 50 to 300 kg/m3) that can then be modified to ice • Neve – snow that has been reduced via partial melting and sublimation (ablation; density = >500 kg/m3) • Firn – Neve that survives seasonal ablation; may be compacted under later accumulations into glacial ice – may take decades or centuries • Glacial ice (density = +/- 850 kg/m3) • Density of fresh water is +/- 1000 kg/m3

8. Glacier Movement • Not a glacier until it moves • When snow and ice > +/-20m thickness, ice mass too heavy to keep rigid shape • Begins to flow via plastic deformation

9. Glacier Flow Rates • Movement not uniform • Center and top portions move faster • Sides and bottom move slower due to frictional drag against valley floor and walls.

10. Glacier Flow Overhead view of an alpine valley glacier showing the relative speed of ice movement Physical Geography.net

11. Glacier Flow Long cross-section view of an alpine valley glacier showing the relative speed of ice movement Physical Geography.net

12. Glacier Flow • Accumulation in broad, erosional basin • Constricted down valley by convergence of narrowing – ice flow compression in central section of the glacier • Flow lines spread out at terminus as ice is no longer constricted by valley walls. • Snout/Lobe - swollen tongue of ice at terminus due to rapid advance

13. Terminus of Alpine Glaciation • Snout/Lobe - swollen tongue of ice at terminus due to rapid advance • Merged glaciers– two or more – can be quite large

14. Glacier Flow Typical flow pattern in alpine glacier Physical Geography.net

15. Temperate vs.Cold Climate Glaciers • Temperate Glaciers • Pressure melting may occur despite sub-freezing T’s • May lead to basal sliding • May lead to liquified soils beneath glacier • Reduced friction = easier, faster movement (typ. <1m/day but may surge 50 m/day)

16. Temperate vs.Cold Climate Glaciers • Cold Climate Glaciers • move very slowly - no basal sliding • Movement mainly due to internal slippage of the ice over the ground

17. Glacier Mass Balance Two main components: • Accumulation of snow vs. ablation of ice • The Zone of Accumulation - upper reaches of glacier • yearly additions of snow exceed losses (from melting, evaporation, and sublimation) • Glacier surface covered by snow throughout the year in this zone.

18. Glacier Mass Balance Two main components: • Accumulation vs. ablation • The Zone of Ablation - below the zone of accumulation • losses of snow and ice from melting, evaporation, and sublimation are greater than the additions • Firn Limit/snow line separates these two zones

19. Glacier Mass Balance • Lag time possible (up to decades) between accumulation surplus and actual glacial advance Physical Geography.net

20. Glacier Mass Balance Figure 17.7

21. Glacier Mass Balance • Can experience rapid forward surge (10 to 20 m/day - greater with basal sliding) – related to past large snow inputs. • Lag time possible (up to decades) between accumulation surplus and actual glacial advance

22. Glacial Ice Loss • Due to two processes: • Ablation • Melting • Evaporation • Sublimation • Calving • Occurs when glacier terminus reaches large body of water. • Portions of the glacier ice break off into the water body. • Origin of many icebergs - calving of the Greenland and Antarctic ice sheets/glaciers.

23. Glacial Ice Loss • Gangotri glacier - Himalayas Physical Geography.net

24. Glacial Ice Loss • Most glaciers in retreat due to global warming of last 1-2 centuries. • Mass balances of these glaciers are negative because of less snow accumulation or higher ablation • Little Ice Age - global temperatures cooler than present, many glaciers worldwide made strong advances.

25. Glacial Erosional Processes Two major erosional processes occur at the base of a glacier: • Scouring • Plucking

26. Scouring • Rock and sediment, incorporated into the moving glacial ice by partial melting and refreezing, erodes the bedrock by abrasion. • Scouring creates a variety of features • Striations • Glacial polish • Glacial flour/rock flour • Glacial milk

27. Plucking • Plucking - particle detachment by moving glacial ice: • basal ice freezes in rock surface cracks; • ice pulled and plucked out, detaching rock/soil; • greatest on the lee-side (down flow side) of rock mounds, called Roche moutonnee – longitudinal asymmetry due to abrasion on stoss side, plucking on lee side; • Ice extends and spreads apart as it flows over rock mounds, causing crevasses.

28. Glacial Erosional Processes Roche moutonnee/whaleback schematic

29. Glacial Polish Figure 17.9

30. Glacial Movementand Crevasses Figure 17.8

31. Crevasses Figure 17.8

32. Crevasses Figure 17.8

33. Crevasses

34. Crevasses

35. Glacial Landforms Two types: • Erosional • Depositional

36. Erosional Alpine Landforms • Merging Glaciers – can be quite large

37. Cliff Caudle, P.G. Environmental Specialist 4 Erosional Alpine Landforms Erosion exerted on bottoms and sides of alpine valleys - guide the flow of glaciers • Talus – ang. debris-freeze-thaw shattering of bedrock • Talus Slopes accumulate along valley walls/on glacier • Bottom and sides of glaciated valley widen and deepen over time • Cross-sectional shape changes over time (U-shaped) • Hanging valleys - small adjoining feeder valleys enter a large valley at some elevation above trunk valley floor • May be due to greater erosion by larger, trunk glacier • May be due to more ice having passed through trunk valley • May have spectacular waterfalls

38. Talus Slope

39. Hanging Valleys Above: Bird Woman Falls, Glacier National Park At left: Milford Sound, South Island, New Zealand

40. Alpine Glacial Landscape Figure 17.10

41. Postglacial Landscape Figure 17.10

42. Alpine Erosional Features Figure 17.11

43. Norwegian Fjord Figure 17.12

44. Glacial Deposition Two major erosional processes add sediment to a glacier: • Abrasion and Plucking • Mass Wasting

45. Glacial Depositional Landforms Glacial drift - All glacial deposits including till and outwash Till - Heterogeneous, unstratified - boulders to clay-size Moraines Depositional landforms composed of till - End - Lateral - Medial

46. Glacial Depositional Landforms End Moraines Terminal moraine - farthest advance of a glacier. Recessional moraine – mark halts in retreat of glacier

47. Alpine GlacialDepositional Landforms End Moraines/terminal moraines

48. Alpine Depositional Features Figure 17.13

49. End Moraines End Moraines off the end of Sperry Glacier, Glacier National Park

50. Alpine GlacialDepositional Landforms Moraines Lateral moraine – narrow belt of debris from valley side slopes Medial moraine – merging of two lateral moraines