Processes of Glacial Erosion
The processes associated with glacial erosion are: frost shattering, abrasion, plucking, rotational movement and extending and compressing flow.
Occurs mostly at the base of a glacier and to an extent at the side. It is most effective in jointed rocks or those weakened by freeze-thaw. As the ice moves, meltwater seeps into the joints and freezes onto the rocks, which is then ripped out by the moving glacier.
At its simpliest form, this processes involves the glacier freezing onto rock outcrops, after which ice movement pulls away masses of rock. In reality, as the strength of the bedrock is greater than that of ice, it would seem that only previously loosened material can be removed. Plucking generally creates a jagged-featured landscape.
This process produces much looser material which may fall from the valley sides on to the edges of the glacier to form lateral moraine, be covered by later snowfall, or plunge down crevasses to be transported as englacial debris. Some of this material may be added to rock loosened by frost action as the climate deteriorated to form basal debris.
Is where the debris carried by the glacier scrapes and scrathes the rock leaving striations. This is the sandpapering effect of angular material embedded in the glacier as it rubs against the valley sides and floor. It usually produces smoothened, gently sloping landforms.
Extending and Compressing Flow
This process causes differences in the rate of erosion at the base of a glacier. Maximum erosion occurs:
- where temperatures fluctuate around 0 degrees, allowing frequent freeze-thaw to operate;
- in areas of jointed rocks which can be more easily frost shattered;
- where two tributary glaciers join, or the valley narrows, giving an increased depth of ice; and
- in steep mountainous regions in temperate latitudes, where the velocity of the glacier is greatest.