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Wind is an important agent of Deposition and transportation. It's role as an Eroder remains questionable.

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Introduction

Wind is an important agent of Deposition and transportation. It's role as an Eroder remains questionable. No deserts are completely rainless although parts of the Libyan and Chilean deserts approach complete aridity. In such places erosion is extremely slow, although occasional showers can have sudden catastrophic effects. Trujillo in Peru received only 1.4 inches of rain between 1918 and 1925, but during March 1925 it received 15.5 inches, of which 8.9 inches fell in the three days 7-9 March. Such events apart, the present work of landscape development are controlled by the wind. (Outside the true deserts, vegetation prevents wind from being a significant agent or erosion), although it can carry enormous quantities of dust far beyond the deserts and can move sand and dust into characteristic depositional forms. It is certain that wind cannot be responsible for most of the eroded landforms of present day deserts, and it is also certain that many of the landscape features of the African and Asian deserts were produced in times of wetter climate. In the Sahara, for instance, there are numerous old lakebeds, which have been dry for a great length of time. ...read more.

Middle

Two of the largest hollows attributed to deflation by wind are the P'ang Kiang hollow in Mongolia which is 5 miles wide and 200 to 400 feet deep, and the Big Hollow in Wyoming, USA, which is 9 miles long, 3 miles wide, and 150 feet deep. It is probable that, although there is no general base-level of erosion for wind deflation, wind cannot be effective below the level of the water table so there is a local limit to the depth of deflation hollows. The main action of wind is not erosive, but in transport and deposition. Wind picks up dry dust and can carry it high into the atmosphere. Nearly a quarter of a million square miles of northern-eastern China are covered with Loess, or wind-borne dust, which has been carried out of the Gobi Desert by winds associated with the winter high pressure system. It was deposited in areas of the increased rainfall and bound by the growing steppe grasses. The grains of loess are often cemented together with calcium carbonate, and being very porous loess preserves steep slopes in the face of many cliffs where cave habitations have been cut. ...read more.

Conclusion

Seif dunes are long sand ridges of irregular shape and variable length. Many seifs in the Egyptian desert are up to 300 feet and 1800 feet wide; some are over 200 miles long. While these figures may represent the largest known, they do, at least indicate that seif dunes are very large features, especially when compared with the barchans. Seifs seem to be developed where there are dominant winds from a different direction from the prevailing ones, which have accumulated the sand. The figure below, shows the development of a barchan into a small seif by the action of wind from two directions. Both seifs and barchans tend to form in families, but the two types are seldom found in association with each other. In contrast with mobile barchans and seifs Bagnold recognised several other types of sand accumulation all of which are stationary. Whalebacks, or flat topped sand ridges extending parallel to the wind direction, occur particularly in Egypt where they may be 100 miles long, 2 miles wide and 150 feet high. Bagnold regarded whalebacks as remnants of seif dunes. Much smaller features are the sand-shadows, which accumulate in the lee of obstructions and are built up by wind is funnelled round them, as at the exits of Wadis. Both shadows and drifts are destroyed if they move downwind (see below) ; ...read more.

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