Describe the processes responsible for ice movements. (20)Explain what factors influence the rate of glacier ice movement. (25)

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Thomas Levick

describe the processes responsible for ice movements. (20)

Explain what factors influence the rate of glacier ice movement. (25)

A. Describe the processes responsible for ice movements. (20)

There are three main processes which are responsible for ice movements, these are; Internal deformation, basal sliding and subglacial bed deformation.

Basal sliding this is the process by which a warm based glacier undergoes thawing at its base. This is due to the melting point of the ice being lowered by increased pressure and friction caused by the ice. This in turn causes the accumulation of a thin film of water along the subglacial base. A part of basal sliding is ice creep, Ice creep is where the ice flows around or over obstacles on the bed. The subglacial surface is often rough and full of obstacles such as areas of resistant rock. When a glacier meets an obstacle on the bed it does not often flow straight over or around the obstacle, there is a slight pause before the ice negotiates the obstacle. The reason for the pause is because the obstacle protruding into the base of the ice mass causes an increase in pressure within the ice on the upstream face of the obstacle. thus increasing the rate of ice deformation around the obstacle, allowing the ice mass to smoothly pass over or around the object. (which can form a roche moutonee)

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Another process that controls the flow of a glacier is a process called sub glacial bed deformation. This is where lose sediment at the bed of the glacier moves enabling the glacier to move more freely over the bed. In order to do this the subglacial bed has to be a warm based glacier, i.e. the glacier has to have a film of melt water at the base. The deformation occurs when the water pressure in the pores or spaces between the sediment grains increases sufficiently to reduce the resistance between the other grains. This allows the sediment grains to ...

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