Easterbrook, Don J. Department of Geology, Western Washington University, Bellingham, Washington.
- Movement of particles by wind
- Eolian abrasion and erosion
- Sand dunes
- Links to Primary Literature
- Additional Readings
Topographic features formed mainly by wind in regions with much loose sand, silt, or clay. An estimated 500 million metric tons (556 million tons) of dust per year are transported by the wind. Airflow in wind can be either laminar or turbulent, but is mostly turbulent. Wind blowing across the land surface contains many swirls and eddies, some of which produce upward components of movement. Generally, the higher the mean wind velocity, the greater the amount of upward turbulence. The ratio of the velocity of upward turbulent gusts near the ground to mean wind velocity varies, but it averages about 1:5. Thus, particles whose settling velocities are lower than one-fifth of the mean wind velocity are likely to be conveyed upward by wind gusts and transported downwind. Larger particles remain mostly close to the ground until unusually high gusts lift them up. Small eddies occur under most atmospheric conditions, unless the air is unusually thermally stable. As wind velocity rises, corkscrew eddies develop with axes parallel to the mean wind direction; and larger, horizontal eddies, measured in hundreds of meters, are superimposed on the smaller, corkscrew eddies. See also: Clay; Dust storm; Laminar flow; Sand; Velocity; Wind
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