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How and why do glaciers erode?

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Introduction

How and why do glaciers erode? Glaciers are found where temperatures have stayed below 0?C for a period of time long enough that the snow from one winter survives the following summer. Then it will be covered with fresh snow in the winter. As the amount of snow falls it is compacted, and through partially melting and refreezing air is removed. Over time a glacier will form. Before an area is glaciated it will be affected by tundra conditions. These are extremely important, with regard to the later erosion processes, because they determine the amount of debris available for use in abrasion. The more joints in rocks that are exploited by freeze-thaw weathering then there will be an increase in the tools available for erosion when the glacier forms. If the area is tectonically active or the rocks are well jointed then the amount of glacial erosion may be increased (or continued) due to the increase in (or constant supply of) ...read more.

Middle

There are two main ways in which glaciers erode the bedrock that they are passing over, abrasion and plucking. Abrasion occurs when the debris being carried by the glacier moves to the base of the glacier and is carried across the bedrock. So long as the debris being carried is not sufficient to stop impede the movement of the glacier then there will be erosion of the bedrock by the debris. For there to be effective glacial erosion due to abrasion there must be a continuous flow of particles to the bed of the glacier, otherwise the debris becomes polished and ineffective. The second main form of glacial erosion is 'plucking' this involves two processes, deformation and regelation. In deformation the glacier passes over the bedrock and surrounds a particle on the surface of the bed, the tractive force of the glacier then overcomes the frictional force holding particle into the bedrock and 'plucks' it away from the rock. ...read more.

Conclusion

If the mass balance of the glacier is increased then the movement of the glacier will be increased proportionally. For there to be an increase in the mass balance then there must be more accumulation (inputs: e.g. direct precipitation or avalanches) than ablation (outputs: melting, evaporation, wind deflation or carving of ice from the glacier). In 1950 Shumski said that the mass balance of a glacier was 'the energy of glaciation', this can be seen (combined with Weertman's statement) to be the case by comparing the Franz Joseph and Meserve glaciers, where the higher mass balance of the Franz Joseph (due to the higher precipitation) leads to melting at the base because the glacier reaches the pressure melting point. This increased meltwater makes the glacier move faster, as does the increased size of the glacier, and so it erodes more than the cold based Antarctic glacier. There may also be seasonal differences within glaciers, where ablation or accumulation may increase or fall due to the seasonal change in weather conditions. ?? ?? ?? ?? Page 1 ...read more.

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