GLACIERS

Glaciers consist of snow so deep it has compacted into ice.
Glaciers flow downhill under the force of gravity.
If the end of a glacier is moving forward faster than it is melting, the glacier is said to be advancing. If it is melting faster, then it is said to be retreating. The mass balance of a glacier refers to how its total mass is changing.
As glaciers move, they erode the surface they move over, carving out valleys and other land forms.
Glaciers also pick up rock debris and sediment, which increases abrasion on the surface under the glacier and is later deposited when the glacier retreats.

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