عنوان مقاله [English]
نویسنده [English]چکیده [English]
Wind deposits are caused by erosion, displacement and discharge of non-solid materials by wind. Sedimentary deposits are caused by major wind, sandy hills and clay deposits.
Sandstones include hills or sandy ridges that are caused by wind blowing. They are usually found where a sand source is available and the wind is strong enough to erode and carry sand particles of the same size, and where sand deposits on the surface of the earth. These conditions are usually found on inlands, through sandy beaches with coastal winds, close to creeks with exposed sandy floors during dry seasons, and in desert areas where sandstone and rocks’ breakdown create sand. In addition, the moraine-like washed sediments and areas of moraine sandy lake beds often provide a sandy source. Since wind speeds are rarely strong enough to lift sand grains more than 1 to 2 m above ground level, sand grains are displaced by the "gradual advance" process (3), so that the grains move in approximate range of 0.5 to 1 meter above the ground through collisions and jumps.
Sandy hills are slowly formed with an asymmetric cross-section with a slope of 5 to 10 degrees in the direction of wind and 30 to 40 degrees in the opposite direction of the wind. As long as sand hills are not stabilized by growth of plants, sand hills move along the wind direction because the sand grains of the hills fall from the direction that the wind blows towards the opposite direction (the side on which the sandy hill can not be threatened). The movement of sandy hills is usually less than 30 meters per year.