Contrary to what some people think, these are not “dirty tornadoes.” Whereas a tornado descends from a storm cloud, a dust devil forms from the ground up, and mostly on hot, clear days. The vortex becomes visible as it picks up dust and debris from the terrain.
Dust devils occur when the sun heats up one part of the ground faster than the ground around it. As the hot-spot air draws in surrounding cooler air, it causes a spiraling column that rises. Most grow to 10-30 feet tall with winds averaging 40 mph. But some grow much larger, moving at speeds exceeding 60 mph.
Occasionally, they inflict damage and make news. For example, in late May last year, a strong dust devil ripped shingles off an apartment complex in Spokane. In 2010, another one collapsed a tent at a bicycle swap meet in Seattle.
What’s fascinating is that on any given summer day, dust devils may occur in other parts of the country that no one can see. Because Eastern Washington is so dry in summer, loose dust and dirt is easily whisked into the air which allows us to see to the funnels so well. But not so in places like the Midwest, where high humidity levels keep dust and soil from going so easily aloft.
Following the eruption of Mount St. Helens in 1980, scientists discovered that dust devils are more common than was originally believed. After the weather turned hot and sunny, researchers witnessed hundreds of dust devils flicking about – made visible by the light, powdery volcanic ash.
Dust devils even kick up Martian dirt. In 2012, the Mars Reconnaissance Orbiter photographed one that was 12 miles high, its plume stretching, in the words of Buzz Lightyear, to infinity and beyond.
Nic Loyd is a meteorologist with Washington State University’s AgWeatherNet. Linda Weiford is a WSU news writer and weather geek. Contact: firstname.lastname@example.org or email@example.com.
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