How do Glaciers Form?
Glacial systems
A glacier behaves as a system with inputs, stores, flows and outputs. Inputs to a glacier can be in the form of snow which falls directly onto it or from avalanches that fall from the glacier sides. Inputs mainly occur near to the head of the glacier (the highest point) in the zone of accumulation. During fresh falls of snow air is trapped between the snow flakes. As more snow falls the underlying layers are compressed, the air is squeezed out and the snow becomes firmer, usually termed firn. As more snow accumulates the underlying layers are compressed into ice. Ice without any air (oxygen) turns blue as can be seen in the picture. The large amount of ice is termed a glacier and is basically water held in storage. The ice can flow downhill under the force of gravity. Outputs from the system come in the form of meltwater and evaporation. |
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When a glacier melts it is called ablation. In winter input (accumulation) is likely to exceed output (ablation) as more snow falls during this season.
If ablation exceeds accumulation the glacier will decrease in size.
At present most of the world’s remaining glaciers are retreating.
The Movement of Ice
Ice melts faster under pressure. It will even melt under pressure at subzero temperatures. This helps explain how glaciers flow. In a glacier, the pressure exerted by the mass of ice above melts the ice at the bottom of the glacier, providing a lubricating film of water which allows the glacier to slide downhill under the force of gravity.