Deserts and Winds

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Traditional Aboriginal Knowledge

Deserts and Winds

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Wind as a Geologic Agent
Sediment Transportation by Wind
Wind Erosion
Wind Deposits:
Sand Dunes:
Surface Processes in Deserts

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University

Wind as a Geologic Agent Wind is common in arid desert regions because:

Sediment Transportation by Wind

Wind transports sediment near the surface by saltation. Just as in the bed load of streams, saltation refers to short jumps of grains dislodged from the surface and jumping a short distance. As the grains fall back to the surface they may dislodge other grains that then get carried by wind until they collide with ground to dislodge other particles. Smaller particles can become suspended in the wind and may travel for longer distances.


Sand Ripples - Occur as a result of larger grains accumulating as smaller grains are transported away. Ripples form in lines perpendicular to wind direction. Wind blown dust - Sand sized particles generally do not travel very far in the wind, but smaller sized fragments can be suspended in the wind for much larger distances.

Wind Erosion Wind

can be effective agent of erosion anywhere that it is strong enough to act. Wind can erode by deflation and abrasion. Deflation is the lowering of the land surface due to removal of fine-grained particles by the wind. Deflation concentrates the coarser grained particles at the surface, eventually resulting in a surface composed only of the coarser grained fragments that cannot be transported by the wind. Such a surface is called desert pavement



Ventifacts are any bedrock surface or stone that has been abraded or shaped by wind-blown sediment in a process similar to sand blasting.


Yardangs are streamlined wind-eroded ridges commonly found in deserts


Wind Deposits

Wind can deposit sediment when its velocity decreases to the point where the particles can no longer be transported. This can happen when topographic barriers slow the wind velocity on the downwind side of the barrier. As the air moves over the top of the barrier, streamlines converge and the velocity increases. After passing over the barrier, the streamlines diverge and the velocity decreases. As the velocity decreases, some of the sediment in suspension can no longer be held in suspension, and thus drops out to form a deposit. Topographic barriers can be such things as rocks, vegetation, and human made structures that protrude above the land surface.



Sand Dunes - Sand dunes form when there is (1) a ready supply of sand, (2) a steady wind, and (3) some kind of obstacle such as vegetation, rocks, or fences, to trap some of the sand. Sand dunes form when moving air slows down on the downwind side of an obstacle. The sand grains drop out and form a mound that becomes a dune.
Sand dunes are asymmetrical mounds with a gentle slope in the upwind direction and steep slope called a slip face on the downwind side. Dunes migrate by erosion of sand by wind (saltation) on the gentle upwind slope, and deposition and sliding on the slip face, and thus are cross-bedded deposits.


Dunes may cover large areas and reach heights up to 500m.

Barchan Dunes

Barchan Dunes - are crescent-shaped dunes with the points of the crescents pointing in the downwind direction, and a curved slip face on the downwind side of the dune. They form in areas where there is a hard ground surface, a moderate supply of sand, and a constant wind direction.


Transverse Dunes

Transverse dunes - are large fields of dunes that resemble sand ripples on a large scale. They consist of ridges of sand with a steep face in the downwind side, and form in areas where there is abundant supply of sand and a constant wind direction. Barchan dunes merge into transverse dunes if the supply of sand increases.


Linear Dunes

Linear Dunes - are long straight dunes that form in areas with a limited sand supply and converging wind directions.


Parabolic (Blowout) Dunes

Parabolic (also called blowout) Dunes - are "U" shaped dunes with an open end facing upwind. They are usually stabilized by vegetation, and occur where there is abundant vegetation, a constant wind direction, and an abundant sand supply. They are common in coastal areas.


Star Dunes

Star Dunes - are dunes with several arms and variable slip face directions that form in areas where there is abundant sand and variable wind directions.



Deserts are areas where rainfall is less than 250 mm (10 in.)/year, or where evaporation exceeds precipitation. Thus, deserts are areas that we think of as arid. Origin of Deserts Deserts originate by several different mechanisms that result in several different types of deserts.

Surface Processes

Surface Processes in Deserts The same geologic processes operate in deserts as in other more humid climates. The difference is the intensity to which the processes act.
Streams and Fluvial Landforms
Surface Waters
Surface waters are rare in deserts. Streams that do flow in deserts usually originate at higher elevations and supply enough water for the stream to pass through the desert region. Streams in deserts tend to be intermittent, that is they flow only during rains. For this reason, flash floods and braided streams are common.

Inselbergs - The word inselberg means island mountain in German. Inselbergs are steep sided hills that rise above a surrounding relatively flat plain. They appear to form because the rock making up the inselberg is more resistant to erosion than the rocks that once made up the surrounding plain. Once an inselberg forms, it sheds water due to its steep slopes, and its steep slopes tend to not develop soil. The surrounding less resistant rock collects this water and is subjected to more rapid rates of chemical weathering. Thus as the surrounding plain is reduced by stream erosion and weathering faster than the more resistant rock. Inselbergs are common in desert regions, although they can also occur in other areas where differential erosion takes place.


Desertification Desertification occurs as a result of climatic changes, such as changing positions of the continents, or changes in ocean and air circulation patterns. Human impacts, such as overgrazing, draining of land, and lowering of the groundwater table, can also contribute to desertification. As vegetation dies out, the soil is more easily eroded and may be lost so that other vegetation becomes destabilized. Since soil can hold moisture, if the soil erodes, the area may become arid, and the desert expands.