A dust devil is a strong, well-formed and relatively small, rapidly rotating whirlwind that stirs up dust, sand, leaves, and other material as it moves across the ground. They range in size from eighteen inches in width and a few yards in height to the rare and large ones that are over thirty feet in width and a thousand feet high. Typically they only last a few minutes but once in a while one can last as long as a few hours. In one form or another they rank second only to turbulent eddies as the most common form of a vortex on the planet.
Dust devils form on late mornings or afternoon on hot days after the sun has had time to warm up the ground and air. Any dry terrains such as deserts or cleared agricultural areas are prime dust devil breeding grounds. They form from the ground up, unlike tornadoes which form from the cloud down. A dust devil will form when a layer of air lying just above the ground is heated and this layer of heated air will begin to rise. Cooler air will then fill the space left by the rising warm air. At some point it will begin to spin. The speed of the spin depends on how fast the warm air rises. The faster the air rises, the faster the spin. It is not until the dust devil is spinning fast enough to pick up matter such as leaves, grains of sand, dust, etc. that it becomes visible, and while the speed of a dust devil doesn’t compare to a tornado, it will usually gain speed up to around twenty five miles per hour.
Unlike tornadoes or hurricanes, dust devils will rotate either clockwise or anti-clockwise. Due to their size, the earth’s rotation has no effect of the direction of the spin and each direction occurs with equal frequency although certain land features such as hills in the area can affect the which way the dust devil will spin.
These spinning vortexes are common the world over and at any given moment there are as many as ten dust devils dancing around. They are also known by many different names: whirlwinds, sand devils, willywillys, sand augers, desert devils or the dancing dervish. Among the Navajos, dust devils are known as “Chiindii” and are believed to be the ghosts or spirits of the dead. Chiindiis spinning counter clockwise are bad spirits and a Chiindii spinning clockwise is said to be a good spirit.
Generally speaking, dust devils are small and harmless, although the larger ones have been known to cause some damage to unsecured buildings and injure wild life and live stock. Also, they can cause respiratory distress especially for those who have allergies or problems breathing. If you live in an area that is prone to dust devils, it is advisable to always carry with you some form of protective mask. Fortunately dust devils are seasonal phenomena and around during the late spring and hot summer months only.