Sandstorm is a wind storm that carries sand through the air. The wind-driven sand forms a low cloud near the ground. Most of the sand particles do not rise higher than 10 feet (3 meters), but some grains rise up to 50 feet (15 meters). The grains average from 1/170 to 1/85 inch (0.15 to 0.30 millimeter) in diameter. During sandstorms, wind speeds exceed 10 miles (16 kilometers) per hour. The storms may last three to five hours. They tend to form during the day and die out at night.
Most sandstorms occur in the sandy areas of deserts. Some occur on beaches; dry riverbeds; or deposits of gravel, sand, and silt called alluvial fans. Sandstorms reduce visibility and thus endanger motorists on desert roads. They also damage crops. In the United States, a sandstorm is reported when blowing sand reduces visibility below 5/8 mile (1 kilometer).
During a sandstorm, most of the sand moves by a jumping or bouncing motion called saltation. When the wind gains speed, grains of sand roll forward and collide with other grains, causing many of them to bounce upward. Some of these grains fall and then bounce up again after striking a pebble or rock.
