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## The Effects of Wind on Deserts The effects of wind on deserts can be seen in the following: - The speed of wind, carrying the dust and sand particles. - The nature and amount of sand brought by the wind. - Water features like lakes, streams, etc. in the close-by area. - The nature of vegetati...

## The Effects of Wind on Deserts The effects of wind on deserts can be seen in the following: - The speed of wind, carrying the dust and sand particles. - The nature and amount of sand brought by the wind. - Water features like lakes, streams, etc. in the close-by area. - The nature of vegetation on the land. - The nature of the surface, where the formation of a sand dune takes place. ### Shifting or Migration of Sand Dunes - Sand dunes often move in the direction of the wind. - The dunes of Trade Wind deserts take definite forms, moving in a definite direction. - *Migratory sand dunes* are uncertain and dangerous. - When they migrate with the wind, they damage towns and villages. - The shifting of a sand dune can be checked by the growth of vegetation on the wind-ward slope. - Dunes are found in the tropical deserts of Asia and Africa. ### Types of Dunes The following two types of sand dunes are seen in the tropical deserts: - **Barchan:** These are moon-shaped dunes which advance steadily before winds that blow from a particular direction. They are found in the deserts in the Sahara. Barchans are initially formed by an accumulation of sand at an obstacle, such as a heap of rocks. They occur transversely to the wind, so that their horns thin out and become lower in the direction of the wind. The windward side is convex and gently-sloping while the leeward side (being sheltered) is concave and steep. The crest of the sand dune moves forward as more sand is accumulated. - **Longitudinal Dunes or Seifs:** These are long and narrow sand-ridges which grow parallel to the direction of the prevailing wind. They are found in the interior parts of deserts. In the Libyan desert, they are known as Seifs (means 'sword' in Arabic). In the Thar Desert they are confined to the western margin, where the force of south-west monsoon influences their formation. An important feature of such a dune is that in its crest line there are rise and fall patterns. Seifs are found in the Sahara, Iran, Thar Desert (India) and West Australia. *** ***Figure 10.9: Barchan*** - The migration of the barchans is a threat to desert life. - They sometimes encroach on an oasis, burying palm trees or houses. - Long-rooted trees and sand-holding grasses are planted to halt the advance of the dunes in order to prevent the fertile land from being devastated. *** ***Figure 10.10: Longitudinal sand dunes***