Glaciers_lecture

Glaciers_lecture - At its maximum about 20 thousand years...

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At its maximum about 20 thousand years ago, an ice sheet covered most of Canada and part of the northernmost U. S. Today in the Northern Hemisphere an extensive ice sheet covers only Greenland.
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A thin, delicate snowflake matures on the surface of a glacier, transforming into a compact grain, the ingredient of “old snow,” or firn. This is the first stage of creating glacier ice.
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Internal motion has sheared this glacier ice into streaks that resemble metamorphic foliation in gneiss. This is “nice gneiss ice!” Black = ice devoid of bubbles; white = ice crowded with microscopic gas bubbles.
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As glacier ice continues to metamorphose, tiny interlocking crystals become larger, just as mineral grains in a rock increase in size during metamorphism.
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A pocket knife provides the size scale of ice crystals in an old, mature glacier such as the Malaspina Glacier, Alaska.
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A valley glacier, also known as an Alpine glacier, consists of a zone of net ice accumulation at high elevation and a zone of net ice wastage at lower elevation. Snow covers the ice in the zone of net accumulation.
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We can monitor internal motion in a glacier by inserting a flexible pipe, then following its progress down-glacier. Motion is accomplished partly through slippage of the entire ice mass over the bedrock, and partly through internal deformation.
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In a temperate glacier the internal temperature profile from top to bottom is exactly at the freezing point of water. In a “cold” or polar glacier the temperature is far below freezing
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This note was uploaded on 09/14/2009 for the course GEO 401 taught by Professor Lassiter during the Spring '08 term at University of Texas.

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Glaciers_lecture - At its maximum about 20 thousand years...

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