Glacio-Fluvial Deposits

10. Landform by the Action of Wind

(Also called Aeolian=Wind )

Wind is also an important agent of denudation. Wind action is mostly limited to arid and semi- arid areas of the world, where the absence of vegetation cover and the presence of extensive desolate rocks, help in erosional, transportation and depositional processes.

There is a definite pattern to the location of world deserts. Almost all the deserts are confined within the 15° to 30° north and south latitudinal belts, also known as the trade wind belts.

♤ Aridity is the result of lack of water, which is dependent on the mean annual rainfall.

♤ These areas are affected by cold currents. These cold currents ensure that there is little moisture available to condense and form clouds. The coasts of western North and South America and Africa display such conditions.

♤ Continetiality is also a major reason for the development of arid and semi-arid conditions. Air descending from mountainous areas warms and dries by compression, little rainfall forms and it results in aridity. Central areas of continents are also dry because air moving over landmasses does not absorb large amounts of water vapour.

About one-third of the land surface of the world can be classified as arid, semi- arid or dry. The major deserts regions of the world include the Sahara desert, Arabian Desert, Kalahari, Namib, Atacama deserts, Great Australian desert, desert of the south-west U.S.A and Mexico.

The combined effect of the erosional activity of wind and water in the arid and semi-arid regions give rise to the following types of surfaces.

♤ Erg (Sandy or True Desert): The erg in the Sahara and Saudi Arabia, and koum in Turkmenistan are the true sandy deserts. They consist of vast, almost horizontal, sand sheets or of regular dune lines, or of an undulating sand sea.

♤ Stony Desert: In a stony desert, horizontal sheets of smoothly angular gravel cover the surface. This is known as the reg in Algeria and serir in Libya and Egypt.

♤ Badland: Badland is any landscape characterised by deep dissection, ravines, gullies, and sharp- edged ridges. The name has been given after the arid area in South Dakota, U.SA.

♤ Hamada or Rocky Desert: It consists of large areas of sand and dust, with patches of bare rock. These bare rocks are perfectly smoothened and polished. This type of deserts in Sahara is known as Hamada.

♤ Mountain Desert: Some deserts are found in the highlands, mountain ranges and the plateau areas. The Ahaggar Mountain and Tibesti mountain of Sahara are examples of these deserts.