Wind


WIND is the least effective of the erosional agents, but it does considerably shape the landscape in areas that are arid, flat, near shorelines, or have glacial deposition. Processes associated with wind erosion are term EOLIAN. As with the other agents of erosion, wind both erodes and deposits.

Wind erodes by ABRASION and DEFLATION. Wind picks up the finest materials and can carry them great distances. Larger materials, such as sand grains, are moved by saltation, the bouncing along the surface. The long term effect of eolian saltation may resemble sandblasting of the surface. Deflation is the removal of particles. Topographically, deflation may result in the wind excavating hollows or depressions called BLOWOUTS.

Wind deposits are more commonly recognized. Deposits of wind blown sand form dunes. Dunes are found in deserts, on plains and floodplains, and on beaches. Four important types of dunes are the barchan, parabolic dune, transverse dune, and longitudinal dune. The BARCHAN is crescent shaped and usually occurs as individual dunes in a group. The horns or points of the dune point downwind (in the direction the wind is going). The windward side (side hit by the wind) is convex, and the leeward side (back side, downwind side) is concave. Barchans are noted for their migration, slowly moving downwind as sand blows over the top and slips down the back face. When more sand is available, the dune type that forms is the TRANSVERSE DUNE. These resemble barchans, however, they form connected rows perpendicular to the wind. If vegetation is more abundant, the PARABOLIC DUNE is more commonly found. This shape of this dune is somewhat opposite of the barchan. The horns point upwind, and the cross section shows that the windward side is concave, and the leeward side is convex. The parabolic dunes are sometime called hairpin dunes, because their long horns and curved shape resemble French hairpins. The fourth type of dune is the LONGITUDINAL DUNE. It is a ridge of sand parallel to the wind.


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