Ch. 11 - Glaciers
- 2. Glaciers Thick mass of ice - accumulates on land - flows downhill - caused by large snowfalls in winter and ____________
- 3. Types of Glaciers 1) Valley (alpine) - smallest glaciers - occupy valleys formerly carved by streams
- 4. Types of Glaciers 2) Piedmont “pied” = French for “foot” - valley glaciers coalesce at base of steep mountain front
- 5. Types of Glaciers 3) Ice caps - cover upland & plateau areas - not confined to valleys - smaller in extent than ice sheets Ex: Iceland
- 6. Types of Glaciers 4) Ice Sheets - largest glaciers - cover continental regions - today: Greenland & Antarctica
- 7. Ice sheets - several 1000’s feet thick - flow outward from central high spot - covers all but highest elevations
- 8. Ice shelves Occur where ice sheets flow into oceans - large flat masses of ice attached to land by one or more sides
- 9. Glaciers: Sediment Transport: High capacity – High competency –
- 10. Erosion Methods 1) Plucking – meltwater gets into cracks in bedrock & freezes - pieces incorporated into base of ice (worn flat on one side)
- 11. Striations Scratches in exposed bedrock - indicate direction of glacial movement
- 12. Erosion Methods 2) Abrasion - weight of moving rx & ice scrapes bedrock - occurs at point of contact
- 13. Erosional Landscapes Valley glaciers produce jagged mountain scenery Ex: Rocky Mountains Ice sheets smooth out landscape Ex: Peoria area
- 14. Erosional Landscapes 1) Glacial trough (U-shaped cross- section) Ice widens, deepens, & straightens former stream valleys
- 15. Erosional Landscapes 2) Hanging valley - smaller valley from a tributary glacier is left higher than main valley
- 16. Erosional Landscapes 3) Cirque (“circle”) - occurs at head of glacial trough - steep walls around 3 sides but opens on 4th side
- 17. Erosional Landscapes 4) Horn Sharp pyramid-shaped peak
- 18. Erosional Landscapes 5) Arete Knife-like ridge separating adjacent glacial troughs
- 19. Erosional Landscapes 6) Tarn – lake occupying a cirque after glaciers melt 7) Paternoster lakes - series of lakes that sit in glacial trough
- 20. Erosional Landscapes 8) Fiord Drowned glacial trough after last Ice Age passed Occur where mtns. are adjacent to oceans at high latitudes
- 21. Depositional Landscapes Glacial drift = all sediment deposited by glaciers Two types of drift: a) Till = sediment deposited directly by glaciers (unsorted)
- 22. Two types of drift: b) Stratified drift = sediments deposited by glacial meltwater - sorted by size
- 23. Landforms composed of till 1) Erratic - boulders that differ from underlying bedrock - source area is outside region where they’re found
- 24. Landforms composed of till 2) Moraine – ridge of till Several types: a) Lateral moraine – found only w/ valley glaciers - parallels sides of valley
- 25. Lateral Moraine Material comes from: a) ice scraping valley walls b) rx from cliffs above
- 26. Types of Moraines b) Medial moraine - lateral moraines from joining glaciers merge
- 27. Types of Moraines c) End moraine - associated w/ stationary glaciers
- 28. Types of Moraines d) Recessional moraines - end moraines created as a receding glacier occasionally stabilized
- 29. Types of Moraines e) Terminal moraine - outermost end moraine that marks limit of glacial advance
- 30. Types of Moraines f) Ground moraine - associated w/ receding glaciers - forms behind end moraines - acts to level the land
- 31. Landforms composed of stratified drift Deposited by glacier’s melt water - flows through moraines & picks up sediment - braided stream channels common
- 32. Landforms composed of stratified drift 1) Outwash plains - broad ramp-like surface built in front of end moraines - associated w/ ice sheets (called “valley trains” w/valley glaciers)
- 33. Landforms composed of stratified drift 2) Kettle/kettle lakes - large blocks of stagnant ice buried in sediment - ice melts - creates a depression
- 34. Depositional Landforms Loess - windblown silt deposits
- 35. Loess - associated with meltwater drainages from glaciation - thickest near drainages and thins away from valleys
- 36. Movement of a glacier Two methods: 1) Plastic flow = internal flow - occurs in ice below 50 meters - occurs fastest in center of glacier (less friction)
- 37. Zone of Fracture Upper 50 meters of glacier - brittle - breaks into cracks called “crevasses”
- 38. Movement of a glacier 2) Basal slip Melt water at base of glacier - entire ice mass slips over surface
- 39. Glacial Budgets Zone of Accumulation = area where snow accumulates & ice forms Zone of Wastage = net loss as glacier advances into warmer climates (lower elevations)
- 40. Zone of Wastage Loss of snow & ice is called ablation Ablation is due to: - melting - calving
- 41. Glacial Budgets Snowline = boundary between zone of accumulation & zone of wastage
- 42. Glacial Budgets 1) Advancing glacier – more accumulation than ablation - glacial front advances - snowline drops in elevation
- 43. Glacial Budgets 2) Retreating glacier - ablation exceeds accumulation - snowline rises in elevation - caused by warming trend or decrease in snowfall
- 44. Glacial Budgets 3) Stationary Budget - accumulation equals ablation - total area of glacier is not changing NOTE: Ice is always moving downhill!
- 45. Evidence for past glacial periods (“Ice Ages”) Periodically, northern Europe & N. America covered by great ice sheets Last one melted from Canada <10,000 years ago
- 46. Evidence for past glacial periods (“Ice Ages”) 1) Glacial erosion Ice sheets: polished bedrock in northern regions, striations, recessional moraines Ex: Central Park, New York City
- 47. Evidence for past glacial periods (“Ice Ages”) Valley glaciers: - Yosemite National Park - Yellowstone National Park
- 48. Yosemite
- 49. Evidence for past glacial periods (“Ice Ages”) 2) Pluvial lakes - form during cooler times w/ moderate rainfall - occurred at lower latitudes where ice did not advance
- 50. Pluvial lakes Most evident in Basin & Range region in western U.S. Ex: Lake Manley, Death Valley Ex: Lake Bonneville, Utah (Great Salt Lake is a remnant)
- 51. Evidence for past glacial periods (“Ice Ages”) 3) Decreasing sea level Water is locked onto land by ice Estimated maximum 100 meters lower than present sea level
- 52. Decreasing sea level Evidence: Submerged stream channels on continental shelves
- 53. Evidence for past glacial periods (“Ice Ages”) 4) Crustal Rebound Land readjusts upward after ice sheets melt Hudson Bay region has uplifted 300 meters since end of last ice age
- 54. Crustal rebound
- 55. Evidence for past glacial periods (“Ice Ages”) 5) Lake Missoula Ice dam blocked melt water - formed huge lake that flooded western Montana (half the size of Lake Michigan)
- 57. Lake Missoula Melting weakened ice dam - lake emptied in 1-2 days - discharge ~ 386 million cfs (Amazon discharge = 6 million cfs)
- 58. Lake Missoula Evidence: a) channeled scablands in western Oregon & southern Idaho b) giant ripples of coarse gravel 30’ high, 300’ apart, 2 miles long