Wind Erosion and Deposition

Air is a form of fluid, albeit much less dense than water, and undergoes significant flow when heated and cooled. It readily expands, contracts, and moves horizontally and vertically. Despite the seeming ease through which we move through the air, it is composed of molecules and the molecules exert force when they are in motion. The force is enough to erode, transport, and deposit considerable amounts of materials. The landscape developments related to wind are corporately known as aeolian

processes (derived from Aeolius, the mythical Greek keeper of the winds). The force exerted by air depends on the air’s velocity and the force exerted is proportional to the square of the velocity. This means that as velocity increases,the force rapidly increases. For instance, a doubling in wind velocity from 10 kph to 20 kph quadruples the force of the wind so that seemingly small wind variations can sometimes make significant differences in the work the wind performs. Along land surfaces, wind is able to modify those surfaces by eroding soil and weathered rock material already in small enough pieces to be moved. Known as deflation, this is especially evident in arid areas where there is little vegetation to hold the material. Unlike water, air is not limited to channels and is frequently capable of transporting materials uphill.

Aeolian transport has three modes depending on wind speeds and sizes of materials. The first mode is creep. Traction is when pieces are pushed along on the landscape. The eddying nature of surface wind is able to concentrate energy onto the surface and move materials. The second mode of transport, saltation, is the “skipping” of somewhat smaller pieces over the landscape. The materials are repeatedly picked up and dropped by whirling eddies that cause parabolic “skips” ranging from a few meters to a few tens of meters. The third mode of transport is suspension. This is generally reserved for materials less than 100 micrometers across, and it is through this mechanism that wind can transport materials over very long distances. For instance, satellite imagery observes dust from the Sahara being blown to the Caribbean basin and Mongolian materials being transported eastward far over the Pacific. When the aeolian material is concentrated it becomes a dust storm, which can be hazardous to plants, animals, and people.  However, it has been found that aeolian materials deposited in the world’s oceans provide a source of nutrients for the oceanic food chain.