Glaciers and Glaciations

1. Glaciers and Glaciations

2. Introduction • Definition • Location • Formation • Movement • Features

3. Definition • A thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow

4. Location • Occupy 10% of Earth’s surface • Primarily located in polar regions (Antarctica & Greenland) • But found on every continent • Form above the snow line

6. Formation • New layers form each year • Weigh of overlying layers compresses buried layers • Snow recrystallizes – looks like sugar • Snow begins to grow, air pockets decrease • compacts & becomes very dense • After 2 winters => FIRN

7. Formation • Firn • Generally 16x the size of a snow crystal • ½ as dense as water • Increase in size as the overburden increases • Over time, grows to form even larger crystals • Forms glacial ice

8. Formation

9. Movement • When ice sheet thickness > 18 meters, the ice sheet: • Deforms • Flows • Movement slower at base than at top • Advance and retreat • Surge

10. Movement • Two basic types of movement • Plastic flow • Occurs within the ice • Under pressure, ice behaves as a plastic material

11. Movement • Two basic types of movement • Basal slip • Entire ice mass slipping along the ground • Most glaciers are thought to move this way by this process

12. Movement • Rates of movement • Average velocities vary considerably • Rates of up to several meters per day • Some glaciers exhibit extremely rapid movements called surges

13. Movement

14. Movement • Budget of a glacier • Accumulation + loss = glacial budget

15. If accumulation exceeds loss (called ablation), the glacial front advances

16. If ablation increases and/or accumulation decreases, the ice front will retreat

17. Retreat of the Franz Josef Glacier: The following photographs are selected from a series that show the retreat of the Franz Josef Glacier in New Zealand over a period of 14 years. Respectively, they are from the years 1951, 1957, and 1964. (World Data Center for Glaciology, Boulder)

18. Features • Crevasses • Cracks in the surface of the glacier • Caused by movement

20. Features • Moraines • Long, dark bands of debris • Visible on the top of the glacier • Medial Moraines • Lateral Moraines Barnard Glacier shows several medial moraines. In this case, the thickest medial moraines occur where additional glaciers flow into Barnard Glacier. Source: http://nsidc.org/glaciers/questions/components.html

22. Types of Glaciers • Ice • Ice Sheets, Ice Shelves, Ice Caps, Ice Streams/Outlet Glaciers, and Ice fields • Glaciers • Mountain Glaciers, Valley Glaciers, Piedmont Glaciers, Cirque Glaciers, Hanging Glaciers, and Tidewater Glaciers.

23. Ice Sheets • Greenland and Antarctica • 50,000 square kilometers • Antarctica • 4200 meters thick in some areas • Covers nearly all of the land features except the Transantarctic Mountains • Source of Ice Core Data & Paleoclimate Research

26. Ice Shelves • Occur when ice sheets extend over the sea, and float on the water • Thicknesses: few 100 m to 1000s of meters • Retreating ice shelves may provide indications of climate change

27. 18 February 2003

28. 25 March 2003

29. Ice caps • Mini ice sheets • form primarily in polar and sub-polar regions that are relatively flat and high in elevation

30. Ice Streams & Outlet Glaciers • Ice streams are channelized glaciers • Flow more rapidly than the surrounding body of ice

31. Ice Fields • Similar to ice caps • Flow is influenced by the underlying topography • Typically smaller than ice caps Kalstenius Ice Field, located on Ellesmere Island, Canada, shows vast stretches of ice.

32. Mountain Glaciers • Develop in high mountainous regions • Often flow out of icefields • The largest mountain glaciers are found • Arctic Canada & Alaska • the Andes in South America • the Himalayas in Asia • Antarctica.

33. Types of Glaciers

34. Valley (alpine) glaciers • Commonly originate from mountain glaciers or ice fields • Flows down a valley from an accumulation center at its head • Look like giant tongues • May be very long • Can reach sea level.

35. Peidmont • Occur when steep valley glaciers spill into relatively flat plains • Spread out into bulb-like lobes. The massive lobe of Malaspina Glacier is clearly visible in this photograph taken from a Space Shuttle flight in 1989.

36. Cirque Glaciers • Named for the bowl-like hollows they occupy (cirques) • Found high on mountainsides • Tend to be wide rather than long.

37. Hanging Glaciers • Also called ice aprons • Cling to steep mountainsides • Wider than they are long • Common in the Alps This hanging glacier above Lyman Lake in Washington State may look simply like a mass of snow, but the crevasses are evidence that it really is a glacier.

38. Tidewater Glaciers • Flow far enough to reach out into the sea • Responsible for calving numerous small icebergs Lamplugh Glacier, in Glacier Bay, Alaska, shows the snout of a typical tidewater glacier.

39. Glacial Landforms • Glacial Erosion • Glacial Deposits

40. Glacial Erosion • Glaciers erode the land in two ways • Plucking – lifting of rocks • Abrasion • Rock flour (pulverized rock) • Glacial striations (grooves in the bedrock)

42. Glacial Landforms

43. Glacial Landforms

44. Glacial Landforms

45. Glacial Deposits • Glacial drift – refers to all sediments of glacial origin • Types of glacial drift • Till – material that is deposited directly by the ice • Stratified drift – sediments laid down by glacial meltwater

46. Glacial Deposits • Landforms made of till • Moraines - layers or ridges of till • Lateral moraine • Medial moraine • End moraine – terminal or recessional • Ground moraine

47. Glacial deposits • Depositional features • Outwash plain, or valley train • Kettles • Drumlins • Eskers • Kames

49. Landforms made of stratified drift • Outwash plains (with ice sheets) • Valley trains (when in a valley) • Broad ramp-like surface composed of stratified drift deposited by meltwater leaving a glacier • Located adjacent to the downstream edge of most end moraines • Often pockmarked with depressions called kettles

50. Landforms made of stratified drift • Ice-contact deposits • Deposited by meltwater flowing over, within, and at the base of motionless ice • Features include • Kames • Kame terraces • Eskers