Sizes of Glaciers
It depends on the accumulation of the snow. This occurs when snow builds up and can get bigger with a higher density. It could also become smaller with a lower density by ablation which is the loss of the mass where the ice melts. Therefore because of these two factors glaciers can grow or shrink.
Overall there are three different types of processes in which glaciation affect the landscape Erosion, Transportation and Deposition.
Glacial Erosion
Within Glacial Erosion, there are three different processes within the term glacial erosion. Glaciers are poor at eroding rock unless it is already weakened beforehand. They are:
Abrasion: Abrasion is the scraping of a rock surface when rock frozen to the base and the back of the glacier scrapes the bed rock. The moving particles remove the loose and weak debris from the side of the rock. Plucked debris in basal ice grinds into the bedrock and this grinding leaves long grooves in the bedrock which are usually parallel called striations. This process can also be seen if there are small, curved scar made by vibratory chipping of a bedrock surface by rock which are called chattermarks. Abrasion requires a warm glacier bed.
Plucking/ quarrying there are two names for this process (plucking and quarrying). This is when some ice comes in contact with a joint and the friction on the ice melts some of the ice present. This ice then freezes to the rock and loosens the rock. As the ice moves down the valley it pulls the rock apart and is particularly effective where a glacier flows over rock that has are ready been weakened by frost weathering.
Meltwater Erosion The streams of meltwater that flow along the base of a glacier erode rock in the same way as surface streams. However, water at the base of a glacier is squeezed by the enormous weight of ice and this causes meltwater streams to flow much faster and therefore the erosive potential of meltwater streams is greater than surface rivers. The water flowing under the ice carries material which erodes the bedrock.
Glacial Transportation
By glaciation, many materials are moved such as debris, rocks and stones. Material can be transported at the middle of a glacier or at the surface of a glacier. By meltwater and suspension, smaller material is carried away. Glaciers move by two different processes.
Internal Flow this is the only type that occurs in polar glaciers and also in temperature glaciers. This is where crevasses occur, (the upper portions of glaciers are brittle, when the lower portion deforms by internal flow and the upper portions may fracture to form large cracks). Crevasses occur where the lower portion of a glacier flows over sudden change in topography.
Basal Sliding Meltwater reduces the friction and allows the glacier to slide more easily across the bed. Polar glaciers can’t undergo this method as they are usually frozen to their bed and therefore too cold for this to occur.
Glacial Deposition After eroding and transporting the material, it is deposited, the rock carried away is dropped and these piles are called moraines. There are different types of moraines.
TERMINAL MORAINES: these are found at the furthest point which is reached by glaciers.
LATERAL MORAINES: these are found deposited along the sides of the glaciers.
MEDIAL MORAINES: these are found at a junction of two glaciers
GROUND MORAINES: these are untidy piles which are of various shapes, sizes, and of different rock types.
DRUMLINS are long extended hills of glacial deposition. These would have once been part of the debris carried and then accumulated where more snow would have built up upon it. All glacial deposits are mixed up
Through the processes of glacial erosion, transportation and deposition, glaciers produce many different formations and change the landscape. For example, valleys are formed where there are slat floor with steep sides which are sometimes called glacial troughs, These are U shaped valleys. Glaciers sometimes have tributaries and these U shaped valleys with a water fall at the surface are called hanging valleys. Peaks and ridges are also formed. A knife- edge ridge such as an Arête is formed when two neighbouring corries run parallel and gradually move together closer. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower. A pyramidal peak is formed when corries and Arêtes meet. The glaciers carve away at the top of a mountain and create a very sharp pointed summit.
