Examine the factors influencing the movement of glaciers.

Temperate glaciers move mainly by basal sliding. If the basal temperature is at or above pressure melting point, a thin layer of meltwater will exist between the ice and the valley floor, therefore friction is reduced and enables the glacier to slide over the underlying land. The thickness of the ice influences this mechanism as the thicker the ice is, the lower the temperature at which it will melt and the higher the chance that some water will be available at the glacier base to enhance movement. Large parts of the West Antarctic ice sheet are at basal melting point, so there may be large areas underneath where a layer of water exists.

Basal sliding involves a combination of mechanisms. Slippage is where the ice slides over the valley floor as described above. Creep is affected by the surface over which the glacier slides. If there is an obstacle in the glaciers path, pressure increases and enables it to move as a plastic, either around or over the obstacle. When the pressure is reduced, the glacier then re-freezes. The lower the temperature, the greater the pressure needed to allow this mechanism to take place, which is why it is less likely to occur in cold glaciers. Bed deformation is another mechanism involved in basal sliding. This is when the ice is carried by saturated bed sediments moving beneath it. The factor influencing this is therefore the sediment on the surface over which the glacier moves and the pressure which it imposes on the glacier.

Polar glaciers cannot move by basal sliding as their temperature is below the pressure melting point. They move instead mainly by internal deformation where the ice deforms under its own weight because of gravity, due to the sum of tiny movements on the faces of the ice crystals making up the glacier. This mechanism has two elements. The first is intergranular flow when individual ice crystals re-orientate and move in relation to each other and the second being laminar flow, which is when there is a movement of individual layers within the glacier. This mechanism of movement is affected by, the thickness of the ice seeing as the thicker the ice is the faster the flow will be due to internal deformation, the temperature because the warmer the ice is the faster the flow will be and pressure because increased pressure on the ice mass will force it to move more quickly.

Another factor that influences glacial movement is the gradient. Where there is a reduction in the gradient on a slope, the ice will decelerate and become thicker. This is compressing flow. Where there is an increase in the gradient the ice will accelerate and become thinner, this being extending flow.

Occasionally some glaciers may surge forward about 100m per day. Factors influencing this movement are a steep gradient and a large input such as a snowfall. This is only likely to occur in temperate glaciers where the basal temperature is relatively high and the ice mass is not frozen to the underlying rock.

In conclusion, the velocity of ice flow varies considerably, depending on factors such as the thickness of the ice, the surface over which the glacier is advancing and the amount of meltwater available to lubricate the base of the glacier. Some glaciers creep so slowly that their movement can only be seen over a period of years, whereas other advance at several metres per day. Different factors influence the movement of glaciers depending on the basal temperature of the glacier as this determines the mechanism by which the glacier will move. Glaciers move most rapidly when the gradient is steep, when the ice is fairly thick and when basal temperatures are at or above the pressure melting point.

Emma Alexander U63