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Wind erosion - Coggle Diagram
Wind erosion
Wind erosion
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An area with little plant cover can be severely affected by wind erosion because plant roots anchor sand and soil in place.
Deserts and coastlines that are made of fine, loose rock material and have little plant cover are shaped most dramatically by the wind.
Deflation
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When wind blows over the land, it picks up the smallest particles of sediment. This sediment is made of bits of clay and silt.
The stronger the wind, the larger the particles it can pick up. Slightly heavier particles, such as sand, might skip and bounce for a short distance. But sand soon falls back to the ground. Strong winds can even roll heavier sediment particles over the ground.
In deserts, deflation can sometimes remove the top layer of fine sediment or soil and leave rock fragments that are too heavy to be lifted by the wind. This hard, rocky surface, which consists of pebbles and small broken rocks, is called desert pavement.
Abrasion
When windblown sediment strikes rock, the surface of the rock gets scraped and worn away by a process called abrasion.
Winds bounce and blow sand grains along. These sand grains strike against rocks and break off small fragments. The rocks become pitted and are worn down eventually. If different parts of the rock are of unequal hardness, the softer parts are worn away more rapidly, leaving the harder parts standing out.
Dust storms
When soil is moist, it stays packed on the ground, but when it dries out, it can be eroded by wind.
Soil is composed largely of slit and clay–sized particles. Because these small particles weigh less than sand–sized particles of the same material, wind can move them higher into the air.
Silt and clay particles are small and stick together. A faster wind is needed to lift these fine particles of soil than is needed to lift grains of sand.
However, after they are airborne, the wind can carry them long distances. Where the land is dry, dust storms can cover hundreds of miles.
These storms blow topsoil from open fields, overgrazed areas, and places where vegetation has disappeared.
Sand storms
Even when the wind blows strongly, it seldom carries sand grains higher than a foot or two above the ground. However, sandstorms do occur.
When the wind blows forcefully in the sandy parts of the deserts, sand particles bounce along and hit other sand grains, causing more and more grains to rise into the air.
These windblown sand grains form a low cloud just above the ground. Most sandstorms occur in the desert, but they can occur in other dry regions.
Deposition by wind
Loess
Wind can deposit extremely fine material. Thick deposits of this windblown, fine–grained sediment are known as loess.
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Because wind carries fine–grained material much higher and farther than it carries sand, loess deposits are sometimes found far away from their source.
Dunes
When the wind hits an obstacle, such as a plant or a rock, the wind slows down.
As it slows, the wind deposits, or drops the heavier material. The material collects, which creates an additional obstacle. This obstacle causes even more material to be deposited, forming a mound.
Eventually, the original obstacle becomes buried. The mounds of wind–deposited sand are called dunes.
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Movement of Dunes
Dunes tend to move in the direction of strong winds. Different wind conditions produce dunes in various shapes and sizes.
The wind is constantly transporting material up this side of the dune. As sand moves over the crest, or peak, of the dune, it slides down the slip face, creating a steep slope.
A dune usually has a gently sloped side and a steeply sloped side, or slip face. In most cases, the gently sloped side faces the wind.
The rate of movement for a dune depends on the strength and frequency of wind, the constancy of wind direction, and the size of the dune.
Generally, the larger the dune, the more slowly it moves. Most dunes travel from about 3 to 65 feet per year, depending on their size and the amount of vegetation in the region.
Where strong winds blow regularly in the same direction, large dunes can override and bury whatever lies in their path. Farmland, forests, roads, buildings, and even entire villages may be overwhelmed.
Sooner or later, however, most dunes are anchored by vegetation.