A dust devil in Arizona – By NASA (NASA web page & source file) [Public domain], via Wikimedia Commons
A dust devil is a strong relatively long-lived whirlwind, ranging from half a meter wide and a few meters tall to more than 10 meters wide and more than 1000 meters tall. Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property. Dust devils form when hot air near the surface rises quickly through a small pocket of cooler, low-pressure air above it. A fully formed dust devil is a funnel-like chimney through which hot air moves, both upwards and in a circle. As the hot air rises, it cools, loses its buoyancy and eventually ceases to rise.
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