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All About Glaciers
   
[Svartisen, Nordland, Norway] (LOC) by The Library of Congress on Flickr


Glaciers

 

Glaciers are slow-moving masses of  ice that exist where more snow falls than melts. They occupy about 10% of the Earth's land, mostly in Greenland and Antarctica. As they move, glaciers can widen and deepen valleys, flatten forests and grind boulders into pebbles.

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Icelandic symphony by Daveness_98 on Flickr

Types of glaciers
 Alpine glaciers form on the crests and slopes of mountains and are also known as "mountain glaciers", "niche glaciers", or "cirque glaciers". An alpine glacier that fills a valley is sometimes called a valley glacier.

 

 The largest glacial bodies, ice sheets or continental glaciers, cover more than 50,000 km² (20,000 mile²).

 

 Ice shelves are areas of floating ice, commonly located at the margin of an ice sheet.

 

Ice streams are fast-moving sections of an ice sheet.

 

 

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Large chunk of Ice calving from Glacier by Alan Vernon. on Flickr


Tidewater glaciers are glaciers that terminate in the sea. As the ice reaches the sea pieces break off, or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water
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Glacier du Mont Durand by Olivier Bruchez on Flickr

How do glaciers move?

Glaciers move, or flow, downhill due to the ice building up in the middle, forcing the edges to expand and gravity.
Another type of movement is through basal sliding . In this process, the glacier slides over the terrain on which it  sits, lubricated by the presence of liquid water.

 The speed of glacier movement is partly determined by friction. Friction makes the ice at the bottom of the glacier move more slowly than the upper portion. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center.

 

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The moraine of Hrútafell, Central Iceland. by Cornell University Library on Flickr

Glacier words to know:

Deposition occurs when the moving ice stops and melts, depositing rocks, sand and dirt that it carried along.

 

As the glacier flows over the bedrock's fractured surface, it softens and lifts blocks of rock that are brought into the ice. This process is known as plucking.

 

Glacial till: material directly deposited from glacial ice during deposition.

 

 

 

 

 


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Looking down on the crevasses of Raven Glacier by Alaskan Dude on Flickr

Crevasses form due to differences in glacier velocity. As the parts move at different speeds and directions, shear forces cause the two sections to break apart, opening the crack of a crevasse all along the disconnecting faces

Crevasses make travel over glaciers hazardous. Subsequent heavy snow may form fragile snow bridges, increasing the danger by hiding the presence of crevasses at the surface

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