Willy willy, also known as a 'dust devil'
What is a willy willy or a dust devil? Find out more about how they form.
This phenomenon, most commonly known today as dust devils, is an upward spiralling, dust filled vortex of air that may vary in height from a few feet to over 1,000. They are usually several metres in diameter at the base, then narrowing for a short distance before expanding again. They mainly occur in desert and semi-arid areas, where the ground is dry and high surface temperatures produce strong updrafts.
The initial rotation may be caused by irregularities in the surface. Unlike tornadoes, dustg devils grow upwards from the ground, rather than down from clouds. In the stronger dust devils, a cumulous cloud can be seen at the top of the rising column of warm air. They only last a few minutes because cool air is sucked into the base of the rising vortex, cooling the ground and cutting off its heat supply.
Although they may resemble 'mini-tornadoes', dust devils are nowhere near as powerful or destructive. They travel across the ground and, besides dust, they may also carry other loose debris such as hay; as seen in the clip below.
On September 13th 2000 a dust devil formed at the Coconino County Fairgrounds and caused property damage and injuries. Winds were estimated as high as 75 mph. In another rare incident, three children in a bouncy castle were carried over 10 feet in east El Paso, Texas.