Notes on-Wind as an agent of Gradation (2 pages long)
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Answer:
Wind is an active agent of gradation mainly in the desert. It blows unchecked due to lack of vegetation. The sand and dust particles are carried over greater distance. These get deposited when the wind velocity reduces or when there is an obstruction in the path of the wind. Wind does erosion, transportation and deposition, similar to other agents of gradation and forms the following features (a) Mushroom rock, (b) Sand dunes.
(a) Mushroom rock when the wind blows, particles of sand strike the rock a little above the surface. Since the sand particles are heavier, the sand blasting effect is restricted to a particular height. The centre of the rock is eroded faster than the upper part of the rock forming a feature resembling a mushroom or an umbrella. Mushroom rock has a narrow trunk and is broad at the top and base.
(b) Sand dunes when there is an obstruction in the path of the wind, the wind velocity reduces and the sand particles and dust are deposited forming a mound or a heap of sand. Ripples in the sand show the direction in which the wind is blowing. The dunes are of different shapes and sizes like (tail dune, pin dune. Crescent-shaped dune is known as barchans. It is formed when an obstruction like a bush or a rock may come in the path of the wind.
Dust particles may be deposited hundreds of kilometer away. This wind blown soil is known as loess. The plains of China have a thick deposit of desert soil.