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# Work of Wind The movement of air over the earth’s surface is known as **wind**. It is almost horizontal, although there is a small vertical component. Wind picks up loose debris like sand and pebbles and transports as well as deposits them in another location. Wind can lift and carry sand grains a...

# Work of Wind The movement of air over the earth’s surface is known as **wind**. It is almost horizontal, although there is a small vertical component. Wind picks up loose debris like sand and pebbles and transports as well as deposits them in another location. Wind can lift and carry sand grains away. When the speed of the wind slows down, the sediments brought by wind begin to drop on the ground. If this process continues, it results in a huge expanse of sand known as deserts. ## Action of Winds The wind is the most effective agent of erosion, transportation and deposition, in arid regions. Since there is little vegetation or moisture to bind the loose surface materials, the effects of wind erosion are more pronounced in the desert region. **Wind erosion is operative in the following ways:** 1. **Deflation Hollows:** Deflation involves the lifting as well as the blowing away of loose materials from the ground. The sands and pebbles are carried in the air or driven along the ground. The finer dust and sands may be deposited even outside the desert margins. Deflation results in the lowering of the land surface to create depressions called **deflation hollows**. The Qattara Depression of the Sahara Desert which lies almost **450 feet** below sea level is a good example of deposition. 2. **Sand Dunes:** Dunes are called hills of sand. They are formed by the movement of winds. Such hillocks may be active dunes, constantly on the move. They may also be inactive fixed dunes, rooted with vegetation. Dunes are found in deserts where the sand is being continuously moved, reshaped and redeposited. **Shape and Size**: Dunes have heights ranging from a few meters to about **150 meters**. In desert regions of the Sahara, Thar, and West Australia, there are many sand dunes. They are in different shapes and sizes. In fact, their shape and size depend upon factors such as: * The direction and force of wind * The speed of sand particles * The nature and direction of the wind * Water features close-by * The nature of the ground * The nature of the formation of dunes **The following types of dunes are found in the tropical deserts:** * **Barchan Dunes:** They are crescent-shaped dunes that are usually formed in areas of sparse vegetation and limited sand supply. They are also commonly known as **crescent dunes**. * **Transverse Dunes:** These dunes are formed perpendicular or at a right angle to the prevailing wind direction. They are large, long, and typically occur in areas with abundant sand supply. * **Longitudinal Dunes:** They are formed parallel to the prevailing wind direction. They are also often found in areas of sparse vegetation. * **Star Dunes:** They are formed in areas with strong, multi-directional winds which cause the dunes to take on a star shape. * **Parabolic Dunes:** These are shaped like a crescent moon, but with the points facing upwind. They are typically formed in areas that are semi-arid with some vegetation cover. They are a type of dune that can be seen across the world’s deserts. * **Complex Dunes:** These are often formed when the prevailing wind direction changes over time. They can be a combination of any of the above dune types, resulting in complex shapes and patterns.