Short essay on the Rate of glacier movement

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There is wide variance in the rate of movement (velocity) of different glaciers. Even in a particular glacier, there is differential movement in its different parts. The middle part of a glacier moves most rapidly, while its sides and bottom move rather slowly because of friction against its bed.

Investigation in this regard has shown that only the upper layer of a glacier is composed of fairly rigid ice. At deeper level stress differences may cause the ice to become more plastic.

So the lower plastic ice may move faster than the upper rigid ice. A row of stakes was driven in a straight line across a glacier and they (stakes) moved down the hill; but after a year or two it was found that the row of stakes became curved with convexity facing downwards.

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In case of Mer de Glace, J.D. Forbes found that in summer and autumn the rate of movement was 50-68 cm per day near the centre, while near the sides it was only about 24 cm. In Greenland the rate of movement was much more rapid.

In one case a rate of 30 m per day has been recorded. However, the average rate of movement in summer is about 18 m a day. In general, however, a meter or so per day is a more common rate.

The rate of glacial flow increases with the following: steepness of slope, thickness and temperature of the ice and the narrowness of the valley sides. Movement is retarded if there is a heavy load of debris in the ice.

It is also retarded by friction against rocky channel. It is thus clear that the glacial flow is controlled mainly by stress differences and temperature. It is undoubtedly true that contrary to the running water, ice can move uphill provided the ice is quite thick to give an adequate downward slope at the surface.

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There are sufficient proofs of this in North America and Scandinavia. To give one example, big blocks of rocks from the Swedish plains were carried by Pleistocene ice over mountains 1800 m high and then deposited again on the coastal plains of Norway. Similar examples are available in North America also.

The maximum velocity of the glacial movement is found in the case of Alpine glaciers. The velocity of the Rhone glacier is 97 m per year. In Alaska, some glaciers move about 60 m per day.

However, the Himalayan glaciers show wide variance in the rate of their movement. The Khumbu glacier in the Mt. Everest region moves with a velocity of 37 m per year, while the Baltoro glacier of the Karakoram has the distinction of moving at the rate of 720 m per year.

The most characteristic feature of the glacial movement is that, unlike rivers, glaciers move forward and backward (retreat). The retreat of the glacier is caused by ablation. In the past the glaciers had come down to Badrinath and Gangotri temples, but at present they have retreated.

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However, the term retreat does not imply the actual movement of the glacier in a reverse direction. It actually means that when the balance between the supply of snow and its loss is disturbed, and the conditions are not favourable, the ice-margin shrinks. Then, the glacier is said to be retreating.

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