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Glaciers

Glaciers. Roughly 18,000 yrs ago 30% of the earth’s surface was covered by glaciers. This period is known as the GREAT ICE AGE. Glacier Formation. A glacier is a mass of snow covered ice that moves due to the force of gravity There are 2 types of Glaciers: Valley Glacier (Alpine)

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Glaciers

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  1. Glaciers

  2. Roughly 18,000 yrs ago 30% of the earth’s surface was covered by glaciers. This period is known as the GREAT ICE AGE

  3. Glacier Formation • A glacier is a mass of snow covered ice that moves due to the force of gravity • There are 2 types of Glaciers: • Valley Glacier (Alpine) • Continental Ice Sheet • Snow does NOT melt in summer • Recrystallization of snow to form LARGE crystals of ice (rough and granular) • called FIRN: liked packed snowballs • Lower layers turn to SOLID ICE under the weight of overlying firn and snow.

  4. Snow becomes FIRN

  5. Valley Glacier or Alpine Glacier - This type of glacier can carve out “U”-shaped valleys. **Remember, streams and rivers carve “V”-shaped valleys. • Ex. Glaciers of Alaska

  6. U-Shaped Valley

  7. Continental Glacier or Ice Sheets

  8. The tremendous weight of these glaciers causes it to slowly move outward from the center (some only moving centimeters per year) • When the glacier reaches the sea, chunks break off and become icebergs (this is called calving) • *Smaller ice sheets are called ice caps • GREENLAND: 1.7 Million SQ MI , 3 KM thick • ANTARCTIC: 12.5 Million SQ MI, 5 KM thick

  9. Depth of Greenland & Antarctic Ice Sheets

  10. Glacier Movement

  11. Fastest

  12. As a glacier moves, rocks that are stuck in the ice are dragged across the exposed bedrock. This causes deep scratches and gouges in the bedrock called striations • The direction of the striations shows the path of movement of the glacier

  13. There were 2 periods of glaciations here. Can you tell which was first? Which directions did the 2 glaciers move?

  14. Deposition by Glaciers

  15. glaciers can carry sediment just as streams and rivers can (only glaciers can carry more and much larger sediment) • Since a glacier acts like a bulldozer as it moves, the sediment becomes mixed together and is deposited unsorted • This is called glacial till • If the sediment is deposited by the running melt water from the glacier, it will be sorted (just like from any stream) • This is called outwash

  16. Glacial till - unsorted

  17. Landforms Caused by Deposition

  18. Moraines- deposits of unsorted sediment along the edges and end of the glacier. - The moraine that forms at the end of the glacier (showing its farthest advance) is called a terminal or end moraine (Ex: Long Island)

  19. Erratics- large boulders that have been transported into the area by the glacier- often different in mineral composition than the bedrock of the area

  20. Drumlins- long, smooth hills made of glacial till. - formed when a glacier runs over a moraine made by a previous glacier, “smearing” it out. - The drumlin points in the direction that the glacier is moving

  21. drumlins

  22. Outwash Plains- melt water from the bottom of the glacier carries sorted sediment out in front of the glacier

  23. Outwash Plain

  24. Kames- melt water from the top of the glacier deposits sediment when it flows down off the glacier and reaches the ground. The sediment is deposited as small hills of sorted sediment.Also called “dead ice” deposits

  25. Kettles- circular lakes. Chunks of ice often break off the glacier and are buried in the ground by sediment. As the buried ice melts, the sediment sinks into the hole and the water fills it up

  26. Another type of lake, found in New York, is called a moraine-dammed lake. This is formed when a glacial moraine blocks a river valley from draining. The river floods the valley and forms a long, narrow lake. Ex. the Finger Lakes in upstate New York.

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