Write a brief note on Valley Glacier

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Valley Glacier is a major type of glacier. It is a body of ice occurring in a valley fed by ice accumulating in higher regions on peaks and ridges.

One can imagine a mass of ice on a land surface. If the surface is steeply sloping the ice mass will move quickly and come down as an avalanche. If the surface is moderately or slightly sloping even then the ice mass will move. The movement may be very slow or imperceptible. In solifluction the soil mass moves down the slope by the lubricating function of water and other physical laws.

Similarly, whatever the physics and mechanics of movement, glaciers move down. Their movement can be measured by driving pegs on the surface of the glacier and watching their position in course of time. The daily movement of the Himalayan glaciers ranges from 8 to 15 cm at the sides and 20 to 30 cm in the middle, but at the terminal end the advance of the glacier is inhibited by melting, fall as avalanche and evaporation. This is the position where accumulation of ice is balanced by what is known as ablation, i.e., loss of ice during the year by the above-mentioned processes.

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As the ice moves as a huge solid body exerting enormous pressure on the ground and the sides of the valley it has great power of rubbing, scratching, breaking, plucking, incorporation the broken material, and transporting. Plucking also described as quarrying generally means the breaking away of the pieces of jointed rocks. The melt water wherever it occurs due to high pressure in the glacier enters the joints and after freezing causes expansion of the joints, fractures or bedding planes. Thus, fragments of the bedrocks are loosened and liberated. If such blocks are projected from the general rock surface, they are more easily plucked. Because of its gigantic mass and power, the broken fragments are incorporated in the body of the ice and carried downstream.

Snow and Neve:

Nearer the sources of the glacier the snow is loose un-compacted or powdery. There is air between the frozen particles. Further down the mass increases in dimensions but it may still be semi-crystalline mass, called neve.

The French term neve (firn in German) is applied to snow when its density is .6 to .82. The density of freshly precipitated snow may be less than .1. It gradually increases with the accumulation of snow. The conversion of snow into neve may take several decades. By further compaction, expulsion of interstitial air and crystallization neve becomes glacial ice when the density is more than .82. With further compaction, the density may become .91 when the glacier is called blue glacier.

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