Aeolian (Wind) Processes and Deserts

In the desert belts centered around 10 to 20 degrees north and south of the equator there is very little rainfall. Because of this there is only sparse vegetation. The soil is exposed. The soil is also dry, due to the lack of rain, so the particles have no cohesion as it does when moist. Because the soil and sediments are not protected by a covering of vegetation or held together by roots or held together by cohesion, the wind is free to pick up and carry sediments.

The wind can suspend fine clay and silt particles as windblown dust, perhaps as dust storms. If the dust settles back to the ground in the desert the wind may again pick it up and carry it further. The dust will eventually settle in an area adjacent to the desert in a more humid area with sufficient vegetation to protect sediments from further wind transport. Extensive downwind deposits of windblown dust are called loess.

sand dunes
The wind can bounce sand along the surface in a process called saltation. The sand grains tumble and bounce along the desert floor close to the ground or perhaps as high is several feet in a strong wind. Where they encounter an obstacle they may settle behind it or just in front of it, protected from the wind. Sand may build up here eventually forming a dune. Sand saltates up the gentle incline of the windward face of a sand dune. Sand builds up just over the lip of the dune until it becomes too steep (exceeds the angle of repose) and then it slides down the back side of the dune away from the wind. The steep back side is called the slip face. It lies at the angle of repose.

Over time, layers of sand dune deposits may be preserved as large scale cross-bedded sandstone.

Desert sands are typically well sorted and rounded. The sand grains appear frosted under a micoscope because of constant collisions with other grains during wind transport.

Gravel and rocks are not moved by the wind and remain behind as a desert pavement. The process of removing the clay, silt, and sand and leaving behind the rocks is called deflation.

Sandy deserts are called ergs. Rocky deserts are called regs.