glacier

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Body of ice, originating in mountains in snowfields above the snowline, that moves slowly downhill and is constantly built up from its source. The geographic features produced by the erosive action of glaciers (erosion) are characteristic and include glacial troughs (U-shaped valleys), corries, and arêtes. In lowlands, the laying down of debris carried by glaciers (glacial deposition) produces a variety of landscape features, such as moraines and drumlins.

Glaciers form where annual snowfall exceeds annual melting and drainage (see glacier budget). The area at the top of the glacier is called the zone of accumulation. The lower area of the glacier is called the ablation zone. In the zone of accumulation, the snow compacts to ice under the weight of the layers above and moves downhill under the force of gravity. As the ice moves, it changes its shape and structure. Partial melting of ice at the base of the glacier also produces sliding of the glacier, as the ice travels over the bedrock. In the ablation zone, melting occurs and glacial till is deposited.

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