Lecture28 - Quote of Day Chapter 18 Glaciers and Glaciation...

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Unformatted text preview: Quote of Day Chapter 18 Glaciers and Glaciation efinition: ¾ A glacier is a thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow ypes of glaciers ¾ Valley (alpine) glaciers • Exist in mountainous areas • Flow down a valley from an accumulation center at its head ¾ Ice sheets (continental glaciers) • Exist on a larger scale than valley glaciers • Two major ice sheets on Earth are over Greenland and Antarctica • Ice flows out in all directions from one or more snow accumulation centers Glaciers Figure 18.2 http://www.gsfc.nasa.gov/ftp/earthpix/earthpix2000part2.html Greenland Formation of glacial ice ¾ Glaciers form in areas where more snow falls in winter than melts during summer ¾ Steps in the formation of glacial ice • Snow is recrystallized into a much denser mass of small grains called firn • Once the thickness of the ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals – glacial ice Figure 18.7 Movement of glacial ice Glaciers constantly deform and move (flow) ¾ Three basic types of motion / deformation • Zone of fracture • Occurs primarily in the uppermost 50 meters • Tension causes crevasses to form in brittle ice http://shiro.wustl.edu/pictures/antarctica/crevasse field 600.jpg Crevasse field in Antarctica http://imagingeverest.rgs.org/Media/273 75.jpg Movement of glacial ice Plastic flow • Occurs within the ice • Under pressure, ice behaves as a plastic material http://tvl1.geo.uc.edu/ice/Image/parts/683-7.JPG Alaskan glacier Folds in the ice are evidence of plastic deformation within the ice sheet. http://www.uvm.edu/whale/Glacier3343.jpeg Movement of glacial ice Basal slip • Entire ice mass slipping along the ground • Most glaciers are thought to move by this process rock base of glacier Greenland http://www.petergknight.com/photos/greenland.html Rates of glacial movement...
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This note was uploaded on 04/18/2011 for the course EAS 101 taught by Professor Kirschner during the Spring '11 term at Saint Louis.

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Lecture28 - Quote of Day Chapter 18 Glaciers and Glaciation...

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