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Glaciers

Glaciers . January 21, 2011. Glaciers. Glaciers act as agents of erosion and deposition to help to create unique landforms which you will study in this unit Glacier : A large mass of ice resting on land or floating as an ice shelf in the sea adjacent to land. Glacier. Introduction.

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Glaciers

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  1. Glaciers January 21, 2011

  2. Glaciers • Glaciers act as agents of erosion and deposition to help to create unique landforms which you will study in this unit • Glacier: A large mass of ice resting on land or floating as an ice shelf in the sea adjacent to land

  3. Glacier

  4. Introduction • Ice: An Agent of Erosion • as permanent snow cover increases in thickness, the underlying layers of snow are transformed into ice by tremendous pressure exerted by snow on top

  5. Ice: Agent of Erosion • large volumes of ice behave like plastic and under great pressure they begin to flow out in tongues • the weight and abrasive power of these glaciers changes the landscape

  6. Ice: Agent of Erosion • during last 1 000 000 years, scientists estimate that there have been four glacial advances with the last one ending approximately 10 000 years ago

  7. Why do Ice ages occur?( Theories) • Volcanic eruptions send a layer of ash and dust around the earth in the atmosphere.Solar radiation from the sun is partially blocked resulting in cooling

  8. Why do Ice ages occur?( Theories) • A reduction in the amount of carbon dioxide in the atmosphere reduces the earth's ability to absorb long wave radiation being emitted by the surface. Therefore, not as much heat is trapped by the atmosphere

  9. Why do Ice ages occur?( Theories) • The amount of energy emitted by the sun has cyclic variations. Glaciation coincideswith periods of reduced solar activity.

  10. Why do ice ages occur? (Theories) • Changes in the tilt of the earth's axis as well as changes in its orbit

  11. How do Glaciers Move? • Glacial flow is caused by glacial creep and basal sliding.

  12. How do Glaciers move? • Glacial Creep • due to the tremendous weight and pressure of the glacier, the ice becomes pliable and flows- it flows fastest in the middle of the glacier where it is thickest (i.e. internal flow)

  13. How do Glaciers Move? • Basal Sliding- movement along the bottom of the glacier due to the warmth of the earth and internal streams • This generally only happens in temperate based glaciers, such as in the Alps, where the ground is warmer, allowing the ice to melt

  14. Glacier Surge • The rapid, lurching , unexpected forward movement of a glacier. • A build up of water pressure under the glacier is a cause

  15. The key to whether a glacier advances or retreats depends on the two opposing forces of Accumulation and ablation Ablation is the wasting or loss of material from a glacier.If accumulation > ablation, the tip of the glacier advancesIf accumulation = ablation, the tip of the glacier is stationaryIf accumulation < ablation, the tip of the glacier retreats

  16. How ice Erodes? • Striations: a scratch or groove cut into the surfaces of bedrock by boulders and pebbles frozen into the bottom of a glacier. • Abrasion: is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion

  17. How Ice Erodes? • Glacial Plucking: a process by which sections of the rock, frozen to the bottom of the glacier, are pulled out of place and carried away as ice advances.

  18. How Ice Erodes? • Sheer Weight of the Ice

  19. Physical Geographers Divide Glaciers into two major groups

  20. Continental Glaciers • A major sheet of ice or an continues mass of ice. • Cover the plains and low land areas • 81% of Greenland • 90% of Antarctica

  21. Alpine or Mountain Glaciers • Form in upland and mountainous regions, within larger valleys and basins. • Smaller in Size • Valley Glacier is a common subtype

  22. Cirque • A scooped out, amphitheatre-shaped basin at the head of a alpine glacier valley

  23. Questions • Page 280: 5A, 6A. B and 7

  24. Snow Becoming Glacial Ice • Cold Temperatures • Summer blanket of snow • Glaciers can only form where snowfalls exceed the annual melting over long periods of time • Compacted ice crystals that have not yet been pressed into solid mass form what is called a firn

  25. Cirques • Features Produced by Alpine Glaciation • Cirques • Cirque Mountain, Labrador

  26. After the ice in a cirque is gone............

  27. Tarn A lake occupying the bottom of a cirque eroded by a glacier that has since completely melted

  28. Horn Peak • A rectangular, sharp-pointed peak formed where several glacial cirques erode back into a single mountain

  29. Arete • A knife-edged ridge formed between the steep walls of two or more adjacent glacial cirques

  30. Col • A cirque which breaks the space in a continues ridge forms a col.

  31. U- Shaped valley • A wide, deep valley with a U-shaped cross-section, formed by glacial erosion in a mountainous region. • V shaped river valleys after being occupied by a glacier becomes U-shaped due to erosion

  32. Hanging Valley • A U-Shaped valley cut by a smaller tributary glacier that lies at a higher elevation then the deeper U-shaped valley eroded by the main glacier.

  33. Waterfall/Bridal veil falls • A stream that occupies a hanging valley will enter the main valley as a waterfall

  34. Truncated Spurs • Triangular faces on the vertical walls of the u-shaped valley. • Ex. Upper Kananaskis River, Alberta

  35. Wherever U-shaped valleys have been cut down below sea level, and are flooded by sea, _____________ are formed

  36. Fiords • The result of the drowning of a u-shaped valley by the sea • Fiord coasts are found in Norway, BC, Labrador, New Zealand, Southern Chile and Baffin Islands

  37. Depositional Features • Till • Talus • Moraine • Drumlins • Kettle hole

  38. Unsorted glacial sediment deposited from a melting glacier. Vary from clays to mixtures of clay, sand, gravel and boulders. Usually form plains. Till

  39. Shattered bedrock fragments that accumulate at the bottom of rock slopes. Often form a second slope at the bottom of a steep slope. Talus

  40. An accumulation of unconsolidated material deposited by glaciers. They tend to have many different sized particles, ranging from fine silt to large boulders. Moraine

  41. b) Ground Morainematerial pushed under and compacted under the glacier.

  42. c) Lateral Moraine: material pushed to the side of the glacier

  43. d) Medial Moraine: result of two glaciers moraines coming together with their lateral moraines.

  44. i) Terminal End Moraine: marks glacier’s farthest advance.

  45. ii) Recessional End Moraine: smaller end moraines behind the terminal moraine that form as the glacier recedes

  46. Elongated, streamlined hill deposits of till. Its long axis is parallel with the movement of the ice, with the blunter end facing into the glacial movement. Drumlins

  47. Created from ice melt from a chunk of glacier that was left behind from a retreating glacier. The sides are built up by glacial drift from the melting ice. Kettle Hole

  48. Alpine Glaciers • Alps are high altitude pastures ex: Swiss Alps

  49. Crevasses • Cracks that occur as a glacier moves into a wider part of the valley or encounters a change in slope. • Eastern Baffin Island, Nunavut

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