Dust Devils

Dust Devil 1Admit it, sometime as a kid you spotted a dust devil full of spinning dust or leaves and tried to catch it and stand inside.  Heck I still do it, but I’m not as fast as I once was.  I had never thought about why dust devils occur until I read an article about them in an issue of Current Science, a classroom science magazine.

 

Dust devils occur on patches of open ground that’s warmer than the neighboring terrain, such as a field next to a forest.  The ground of the field gets warmed by the sun and heats the air above it, causing it to rise.  Cold air from the forest rushes in to replace it, creating a column of spinning air called a convective vortex, a dust devil lying on its side.  Along comes a mild 8-12 mph wind, which has enough force to flip the vortex into a vertical position, and there you have it.  Many times the spinning column is not visible, but when it picks up dust, dirt or flotsam (larger items such as leaves, paper, etc.) it looks like a Tasmanian devil cartoon.  There is a variation we call a fire devil that can form along the edge of a wildfire. They can carry a swirling column of burning leaves across containment lines and cause a break over and ruining your day.

 

Around here I’ve never seen a dust devil more than maybe 20 feet tall, but in desert conditions they can get to be over half a mile tall and strong enough to flip a small car.  I once worked on a wildfire at Mesa Verde National Park where one of the safety messages they gave us each morning was to watch out for dust devils.

 

It has been recently discovered that the swirling particles in big dust devils rub against each other and gather a static electrical charge, similar to the shock you get when shuffling your feet across a carpet.  Only think big, because there’s enough voltage in large dust devils to rival the electricity carried in high voltage lines.  All this research on Earthly dust devils originated from wanting to know more about Martian dust devils, which according to surveillance satellites are very common on the red planet.  Because of extreme temperature differences, low gravity, and thin atmosphere, Martian dust devils and can be monsters that are over 5 miles high and scoot across the ground at over 100 miles per hour.  Future astronauts beware.

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