chapter_12_le modified

chapter_12_le modified - Glaciers and Glaciation Physical...

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Steve Kadel, Glendale Community College Glaciers and Glaciation Physical Geology 11/e, Chapter 12
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Glaciers and Earth’s Systems A glacier is a large, long-lasting mass of ice, formed on land, that moves downhill under its own weight Glaciers are part of Earth’s hydrosphere Along with sea ice, glaciers are known as the cryosphere About 75% of the world’s supply of fresh water is locked up in glacial ice
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Formation of Glaciers Glaciers develop as snow is compacted and recrystallized, first into firn and then glacial ice A glacier can only form where more snow accumulates during the winter than melts away during the spring and summer Two types of glaciated terrains on Earth: Alpine glaciation occurs in mountainous regions in the form of valley glaciers Continental glaciation covers large land masses in Earth’s polar regions in the form of ice sheets Glaciation occurs in areas cold enough to allow accumulated snow to persist from year to year
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Anatomy of a Glacier An advancing glacier gains more snow than it loses, has a positive budget End or terminus of glacier advances downslope A receding glacier has a negative budget Terminus of glacier shrinks back upslope Snow is added in the zone of accumulation of glaciers, whereas melting (and calving of icebergs ) occurs in the zone of ablation The equilibrium line , which separates accumulation and ablation zones, will advance or retreat depending on climate
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Movement of Glaciers Valley glaciers and ice sheets move downslope under the force of gravity Movement occurs by basal sliding and plastic flow of the lower part of the glacier, and passive “riding along” of an overlying rigid zone Crevasses are fractures formed in the upper rigid zone during glacier flow Due to friction, glacier flow is fastest at the top center of a glacier and slowest along its margins
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Glacial Erosion Glaciers erode underlying rock by plucking of rock fragments and abrasion as they are dragged along Basal abrasion polishes and striates the underlying rock surface and produces abundant fine rock powder known as rock flour
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Erosional Landscapes Erosional landforms produced by valley glaciers include:
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chapter_12_le modified - Glaciers and Glaciation Physical...

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