Free essay on the concept of Glacial Movement

In mountainous regions where the amount of snowfall is in excess of snow melted during a year, there is a yearly accumulation of snow, which due to overlying pressure and surface melting undergoes a change.

As described above, the snow is metamorphosed into glacier ice. Alpine glaciers generally originate in a cirque or corrie positioned at the mountain top.

If the cirque, the basin of accumulation, is quite large and there is a continued addition of ne’ve’, a tongue-like mass of glacier ice moves out and down from the edge of the snow-field.

Glaciers move gradually downhill from the cirque. They follow the line of least resistance. In other words, they move along the course of a former (pre-existing) river valley.

It is to be noted that the upper portion of the glacier is the zone of accumulation which receives more snow than is lost by the process of sublimation or melting.

The lower portion of the glacier is the zone of ablation where the losses through melting and ablation exceed snowfall. The glacier terminates at a point where ablation exceeds accumulation of snow.

The terminus of a glacier is called Snout. It represents a point where the loss of snow by ablation is equalled by the supply of snow brought down by the glacier.

It is said that the actual mechanism of glacier flow or its movement is very complex and difficult to understand fully. The glacier appears to behave like a viscous liquid, yet it is, in fact, crystalline solid.

It is most probable that the movement of the glacier is controlled by a number of processes such as sliding on the rock floor, plastic deformation, regelation, laminar flow etc.

It has been proved by glaciologist that under certain condition the ice more or less becomes plastic as a result of intermolecular and inter-granular movement. It is to be borne in mind that it is the gravity that is the most important factor for the movement of a glacier.

The term glacial flows’ covers the complex mechanism of down-slope movement of an icy body. The glacial movement involves a combination of different processes such as regelation, granular translation, plastic deformation and laminar flow.

Regelation is the result of pressure within the glacier because of which the melting point of ice is slightly reduced. This liberates molecules of water within the ice-mass. The liberated particles of water form lubricating film helping the ice-grains to move relative to one another.

It results in the downhill movement of the glacier. Granular translation views ice-grains behaving as mechanical units which slide over each other. The glacier which moves rapidly has a lot of such mobile molecules within its crystalline mass.

This results because of the greater supply of ne’ve’ from the upper portion of the glacier or because of the steepness of the slope. This leads to the increase of the strains within the mass. Similarly, the narrowing of the rock-bed which encloses the glacier increases the rate of glacial flow.

The plastic deformation or inter-granular yielding involves intermolecular movement. It does not disturb the solidity of the ice. It also does not change the ice-crystal’s internal atomic structure. This mechanism of glacial flow is considered as the most important.

Laminar flow involves the glacial movement that is the result of a definite thrust along the line of slope. This is the result of solidity of ice and the weight of ice from above.

The base of the glacier creeps and slides along the glide planes (fracture planes) varying its speed with temperature and the presence of any lubricates water beneath the ice.

This is called basal slip which is much less rapid than the internal plastic flow referred to above. Remember that because of this mechanism the upper portion of the glacier flows ahead of the lower portion.

It is to be borne in mind that the unevenness of the valley floor beneath the ice mass may vary the pressure, melting some of the basal ice by compression at one moment, only to have it refreeze later.

This process is thought to be an important factor in the glacial downhill movement. It may be pointed out that because of melting and refreezing a lot of rock debris is incorporated into the glacier.

It is in this way that the basal ice layer has much greater debris content than the ice above (the surface layer). Remember that the surface of a glacier forms a crust which has no flow within its own mass. However, this is carried along above the deeper moving ice.

Despite the various processes which help the glacial flow, each process involves to a certain extent the force of gravity. Therefore all the processes of the complex mechanism of glacial flow may be commonly grouped as gravity flow.