1. GLACIERS AND GLACIATION I

2. Topics n Intro n Glaciers and the Hydrologic cycle n Types n Movement n Glacial landforms –Glacial erosion –Glacial sedimentation –Glacial lakes n Glaciations and global climate

3. GLACIER n A large body of moving ice n Formed on land n Recrystallization of snow n Types: –Alpine (valley) glaciers –Continental glaciers

4. Winter Sea Ice- Beaufort Sea

5. Sea Ice- Bering Sea

6. Timble Glacier, Alaska

8. Valley Glaciers in Denali National Park Courtesy USGS

9. Hydrologic Cycle - 2% of water is Ice

10. What if the glaciers melt?

11. Glaciers-Where they are n Develop where all of annual snow doesn’t melt away in summer – Polar regions – Heavy winter snowfall – High elevations – 85% in Antarctica – 10% in Greenland

12. Types of Glaciers n Valley glacier n Continental Glaciers: –Ice sheets (big) –Ice cap (small)

16. Greenland Ice Sheet: contours indicate elevation of ice sheet above sea level Fig. 12.5

18. Ross Ice Shelf, Antartica

20. Formation and Growth of Glaciers n Metamorphism of Snow n Glacial Budgets – Zone of accumulation – Zone of wastage » Snow line- divides the zones – Negative budget- Receding glacier – Positive budget- Advancing glacier – Terminus- movement reflects budget

22. GLACIERS n Wastage of glaciers (“shrinkage”) – Melting » more melting at lower elevations – Evaporation – Calving into Icebergs » where a glacier flows onto a sea

23. Movement of Glaciers n Valley Glaciers – Gravity driving force – Sliding along its base -basal sliding – Internal flowage- plastic flow – Rigid zone » Crevasses may form here n Ice sheets – Move downward & outward from central high

25. Glacial Erosion n Under glacier – Abrasion & plucking – Bedrock polished & striated – Rock flour washes out of glacier – Polishing and rounding » “Sheep Rocks” – Striations- scratches & grooves on rock n Above glacier – Frost wedging takes place – Erosion by glaciers steepens slopes

28. Erosional Landscapes Associated with Alpine Glaciation n Glacial valleys – U-shaped valleys – Hanging valleys – Truncated spurs » Triangular facets – Rock -basin lakes (tarns) – Rounded knobs- rouche moutonnees

29. Erosional Landscapes Associated with Alpine Glaciation n Cirque - at head of valley glacier – Rock steps » Rock basin lakes n Horn n Arete- sharp ridge

34. Erosional Landscapes Associated with Continental Glaciation n Grooved and striated bedrock – Grooves may be channels n Rounded hills & mountains

37. Glacial Deposition n Till – Unsorted debris n Erratic n Moraine- body of till – Lateral Moraine – Medial Moraine- where tributaries join – End moraine- » Terminal » Recessional

40. Erratic-Alberta, Canada

41. Other Glacial Landforms n Drumlins- –Elongated hills of glacial till –Point down-glacier n Eskers –Sinuous ridges of stratified till –Form in tunnels under the ice sheet –Some times 100km long or more

42. Glacial Deposition n Outwash – Stream-deposited sediment » sorted – Braided streams typical – Esker – Kettle n Glacial lakes

45. Glacial Lakes n Pluvial Lakes- –Due to wetter climate –Examples: Lake Bonneville, Death Valley –Lake Bonneville flood into Snake River Canyon n Proglacial Lakes –In front of the glacial sheet –Ice dammed lakes –Examples: Great Lakes, Lake Missoula

47. Lake Bonneville- 14,000 yrs ago- Utah

48. Lake Bonneville Flood n The lake was up to 1000 feet deep n A ridge on the north side gave way n Peak flow 33 million cubic feet/second n 33 MCF would fill in a tanker train 165 miles long n A raft would move at 75 mph on a wave 300 ft high n Flood left behind giant ripples

51. Glacial ages n Northern Europe & North America heavily glaciated – Peak of glaciation 18,000 years ago – Ended about 10,000 – We are still in the cold part of the climate cycle n Episodic climate changes n At peak glaciation – Average global temperature only 5 degrees colder

53. Effects of Past Glaciation n Glacial ages n Direct effects in North America – Scoured much of Canada – Cut Great Lakes – Deposited till & flattened Midwest – Extensive alpine glaciation in mountains

54. Effects of Glacial Ages n Indirect effects – Pluvial lakes – Lowering of sea level » Fiord – Crustal rebound n Evidence for older glaciation – Tillite – Late Paleozoic glaciation » Evidence for a supercontinent – Precambrian glaciation

55. Causes for glaciation n Astronomical (Milankovitch cycles) –Eccentricity of orbit (100,000 yr cycle) –Wobble of rotation axis (41,000 yr cycle) –Precession of equinox (23,000 yr cycle) n Variations in solar radiation n Atmospheric changes –CO2 (Greenhouse) –Volcanic ash n Tectonic causes –Continents near the poles –Oceanic circulation patterns