Filmmaker Chris Tangey recorded the above video of a fire whirl whisking through the Australian Outback near Alice Springs on September 11. Since then, the clip has swerved from news sites to blogs to social media around the world. In its wake came this simple explanation from New York State climatologist Mark Wysocki on how a fire devil forms, via Life's Little Mysteries:
Like the dust devils that spring up on clear, sunny days in the deserts of the Southwest, a fire devil is birthed when a disproportionately hot patch of ground sends up a plume of heated air. But while dust devils find their heat source in the sun, fire devils arise from hot spots in preexisting wildfires.
"These plumes form in a very small region over the land," Wysocki explained. "They start to rise very rapidly, and as things start to rise, they suck the surrounding air in like a vacuum. Then you get this twisting that begins to resemble a vortex."
As the vortex rises and sucks the blaze up with it, its diameter begins to shrink and, like an ice skater pulling in her limbs to gather speed in a spin, its rotation accelerates.
The Missoula Fire Sciences Laboratory page on fire whirls says they can be anywhere from a few feet to more than a mile in diameter, with winds capable of uprooting trees, picking up cars, and tearing the roofs off houses. They have formed everywhere from a field in Brazil to the slope of a volcano in Hawaii to a city in Japan. Studies offer an indication of just how much damage the spinning flames can cause. Burning in the devil's path may increase by more than seven times and flaming debris shot out of its plume can dramatically extend the range of a fire. The fire whirl that formed during the Chicago Fire of 1871 reportedly shot large boards more than 1,900 feet ahead of the main burn. On the same day, a fire whirl that formed in Peshtigo, Wisconsin, reportedly picked up a house and moved it more than 100 feet.
The laboratory encourages firefighters to use caution when in the vicinity of the flaming devils. At least a dozen firefighters from Japan to California have been injured after the spinning flames sprouted up and took off. The most deadly fire whirl on record occurred after a 1921 earthquake in Tokyo. It was believed to have killed 38,000 people in 15 minutes. A crowd had gathered in an area with low fuel, thinking they were safe, when the vortex swept over them. A fire whirl that formed in Hamburg, Germany, after bombing by the Unites States during World War II grew to more than a mile in diameter and extended three miles into the sky.
You can read more about the science behind fire whirls by reading "Fire Storms," from a 1994 issue of Discover magazine, and "Review of Vortices in Wildland Fire," published in 2011 in the Journal of Combustion.
If you want to watch fire whirls tearing up the landscape, or demonstrations of them being made in a lab, or a homemade video on how to build one in a trash can (not advised), YouTube has a channel just for that.