| IX. Glaciers and Glaciation. |
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UW-Oshkosh Geology
undergraduate student Jon Koenig doing fieldwork in Antarctica.
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A. Glacier = A body of ice formed on land that moves due to gravity.
1.) Glaciers develop where not all of annual snowfall melts in summer
Includes :
2.) Formation + Growth of Glaciers
a.) “Metamorphosis” of snow
Snow --> firn --> Glacial Ice
b.) Glacial Advance vs Retreat
i.) Zone of accumulation
= area of positive annual snow budget.
ii.) Zone of Wasting:
= area where all new snow + some glacier ice melt
iii.) Glacier advances where there is a positive snow-ice budget
Þ Terminus moves forward
iv.) Retreating (receding)
Þoccurs when there a negative snow-ice budget
c. All glacial deposits (sediments) = Drift.
- Till = unsorted (clay- sized) boulders.
- Outwash = sorted, deposited by running melt water
- Erratics = boulders dropped by glacier that does not have a local source (unlike local bedrock)
3.) Glacial Erosion:
a.) At base of glacier:
i.) plucking + Abrasion of bedrock
ii.) Bedrock is polished + striated (scratches and grooves, striations)
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| A. A glacier is a body of ice on land that moves due to gravity. |
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1. Glaciers develop where not all of annual snow melts in summer. |
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a. Polar regions (~85% in Antarctica, ~10% in Greenland). |
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b. Mountains. |
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2. Formation and growth of glaciers. |
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a. "Metamorphosis" of snow to glacial ice (snow to firn to glacial ice). |
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b. Glacial advance Vs. retreat. |
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i. Zone of accumulation: area of positive annual snow budget. |
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ii. Zone of wasting: area where all new snow and some glacial ice melt. |
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iii. All glacial deposits (sediments) = Drift. |
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• Till = unsorted deposit (can include clay minerals, silt, sand, pebbles, boulders) |
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••Outwash = sorted sediment deposited by running melt water (sand and gravel) |
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•••Erratics = boulders dropped by glacier that does not have a local source (unlike local bedrock) |
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| B. Types of glaciers. |
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1. Valley (Alpine or Mountain) Glaciers. |
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a. Gravity drives movement. |
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i. movement on base can be very slow if base frozen, but fast if lubricated with melt water. |
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ii. Ice deforms plastically internally. |
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iii. Upper part deforms brittlely. Fractures on surface = crevasses. |
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b. Landforms: |
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i. Erosional: cirque, horn, U-shaped and hanging valleys. |
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ii. Depositional/ constructional: Moraines (end/terminal, recessional, lateral and medial). |
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2. Ice Sheets ( Continental Glaciers). |
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a. Gravity acts on snow/ice in zone of accumulation and flows outward. |
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b. Landforms: |
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i. Erosional: scoured/striated bedrock, glacial polish, eroded valleys (Great Lakes, Finger Lakes). |
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ii. Depositional / constructional: Moraines (end/terminal, recessional, ground), kames, drumlins, eskers, kettle lakes. |
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| For
more information on Glaciers and Climate Change Check Out: |
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| This
story on the Larsen Ice Shelf Collapse |
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| The
U.S. Geological Survey’s Antarctic Research Page |
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| NASA’s
West Antarctic Ice Sheet Study: |
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| The
Science of Ice at the Museum of Science, Boston |
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| The
National Snow and Ice Data Center |
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| Mountain
Glacier Retreat |
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| The
Cryosphere |
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