A dust devil is a relatively small, rapidly rotating wind that stirs up dust, sand, leaves, and other material as it moves across the ground. Dust devils are also known as whirlwinds or, especially in Australia, willywillys. In most cases, dust devils are no more than 10 ft (3 m) in width and less than 300 ft (100 m) in height.
Dust devils form most commonly on hot dry days in arid regions such as a desert. They originate when a layer of air lying just above the ground is heated and begins to rise. Cooler air then rushes in to fill the space vacated by the rising column of warm air.
At some point, the rising column of air begins to spin. Unlike much larger storms such as hurricanes and tornadoes, dust devils may rotate either cyclonically or anticyclonically. Their size is such that the earth's rotation appears to have no effect on their direction of spin, and each direction occurs with approximately equal frequency. The determining factor as to the direction any one dust devil takes appears to be the local topography in which the
storm is generated. The presence of a small hill, for example, might direct the storm in a cyclonically direction.
Some large and powerful dust devils have been known to cause property damage. In the vast majority of cases, however, such storms are too small to pose a threat to buildings or to human life.