Short notes on Depositional Land Forms (Sand Hills and Loess)

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The transported materials by wind are ultimately deposited when the velocity of the wind decreases. There are two distinct types of deposits; accumulation of sand forming sand hills and that of dust and silt particles known as loess. Besides the deserts and semideserts; the wind deposits are also formed along sea coast, stream courses and in glacial outwash plains.

(i) Sand Hills:

Different types of sand hills are formed due to accumulation of sand grains. Sand shadows and sand drifts occur on the lee side of the obstructions.

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Sand dunes are typical hills formed by sand accumulation. Commonly, they occur in groups. They are termed as dune colonies or dune complexes. They vary in shape, size and height. There are different types of dunes.

Transverse dunes extend transverse to the direction of wind; where as longitudinal dunes extend parallel to the wind direction. Parabolic dunes commonly occur along shore lines with the end points tapering towards wind ward direction. Barchans are the typical sand dunes characteristic of deserts and semi deserts.

There is crescent shaped. The two tapering end points along the directi of wind. All types of dunes are prone to migration along the directi of wind, unless they are held by obstructions.

(ii) Loess:

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The fine dust and clay particles carried by wind are ultimately deposited at a great distance from the place of the origin. The deposits are called loess. Unweathered loess is grey. But, commonly, the loess is buff coloured.

The fine dust and clay consist of angular to sub-angular particles of quartz, feldspar, calcite, dolomite and other minerals. Generally, they are calcareous, permeable and stand out in form of vertical walls. At times, the dust and clay particles are derived from glacial outwash plains and fluvial deposits.

In northen China, the great loess deposits almost cover an area of about 4,00,000 km2 with a thickness of more than 60 to 70 meters. In India, loess is seen in the foot hills of the western Himalays, in Himachal Pradesh and western U.P.

Besides the landforms described above which are aeolian in origin, a large number of landforms are found in deserts and semi-deserts due to combined action of wind and running water.

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In India, the desert land forms are seen in the Thar Desert west of the Aravallies.

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