Wind Action in Deserts: Wind Transport and Deposition

• Wind is able to transport (move) sand and dust particles depending on its speed and flow.
• The effectiveness of wind erosion and transport depend on a number of factors:
• Aeolian movement is greatest where the winds are strong (20km/hr or more), turbulent, come from a constant direction and blows steadily for a length of time.
• The effectiveness and nature of wind transport also depends on the nature of the regolith ( weathered material).
• It is also more effective in areas where there is less vegetation cover which tend to act as wind breaks by absorbing some of the wind’s energy.
• It also depends on the material being transported for example if the material is dry and unconsolidated it can better be transported.
• Optimum wind erosion and transportation occurs in semi-arid parts of deserts.

Wind transport

• Wind moves material by three processes:
• Suspension, saltation and surface creep.
• It is important to note that each of these methods of transportation do not happen in isolation but, often all three take place simultaneous at any given time.

Suspension

• Happens when materials are very fine i.e. less than 0.15 mm in diameter.
• This means that they can be easily picked up by the wind,
• They are then raised to considerable height and carried, in the air, for great distances.
• Sand particles have been on occasion carried from the Sahara desert and deposited in Britain a great distance away.
• Suspension creates dust storms that often reduce visibility in deserts to less than a kilometer.

Saltation

• When wind speeds exceed the threshhold velocity (that is the speed required to move grain particles),
• fine and coarse-grained sand particles are lifted and rise almost vertically for several centimeters before falling again to the ground.
• When they return to the ground they follow a flat trajectory that sees them fall a short distance from where they were picked up but not in the same place.
• The particles are moved by the wind in a leap-frogging and bouncing manner.
• Even in the most severe storms the particles are rarely lifted to more than 2 meters in height thus differentiating this method of wind transportation from suspension.

Surface creep

• As particles are transported by saltation and suspension they may dislodge and push forward larger particles (i.e. those that are more than 0.25 mm in diameter).
• These are too heavy to be lifted from the ground by the wind’s energy.
• However due to continued bombardment by the smaller particles being transport by the other modes of transport they roll and gradually move over the surface of the desert.

Deposition

• Due to the occurrence of obstacles and impediments suchs as vegetation, rocks, dead animal carcases and settlements
• Materials transported by wind are eventually deposited.
• Deposition can also occur due to a reduction in wind energy.
• Wind deposition forms landforms such as barchan and seif dunes.

To access more topics go to the Geography Notes page.