A fire tornado blazes near Curtin Springs, Australia, in a still of a recently released video.
Chris Tangey of Alice Springs Film and Television was filming a wildfire when a small twister touched down, "causing it to build into a spinning flame," according to Australia's WPTV.com. (Watch a video of the fire tornado.)
Also known as fire whirls, fire devils, or even firenados, these whirlwinds of flame are not really rare, just rarely documented, Jason Forthofer, a mechanical engineer at the U.S. Forest Services's Missoula Fire Sciences Laboratory in Montana, said in 2010. (Also see "Fire Tornado Seen Spinning Over Hungary.")
As Tangey told Northern Territory News, "It sounded like a jet fighter going by, yet there wasn't a breath of wind where we were."
—With reporting by Ker Than
Video still courtesy Chris Tangey, Alice Springs Film & TV
Burning Down the House
A fire tornado swirls near a chimney on the roof of a burning house in an unidentified location (file photo).
Fire tornadoes occur when intense heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can tighten into a tornado-like structure that sucks in burning debris and combustible gases, RMRC's Forthofer explained. A fire tornado consists of a core—the part that is actually on fire—and an invisible pocket of rotating air that feeds fresh oxygen to the core.
The core of a typical fire tornado is usually about 1 to 3 feet (0.3 to 0.9 meter) wide and 50 to 100 feet (15 to 30 meters) tall. But under the right conditions, very large fire tornadoes—several tens of feet wide and more than a thousand feet (300 meters) tall—can form, Forthofer said. (Related: "Giant 'Tornadoes' Seen Erupting From the Sun.")
"These really large-scale fire tornadoes occur at least once every year somewhere in the U.S.," he added.
Photograph by Nancy Greifenhagen
Vortex of Hot Ash
A wildfire-induced tornado of hot ash dances across a ridgetop near Rancho Santa Margarita, California, in May 2002.
"We're not totally sure about that, but it's one theory," he said. "It's like if you've ever seen anyone try to burn cooking flour: If you puff it up enough in the air, you can actually burn it. But as it sits compacted in a lump, it won't burn."
Photograph by David McNew, Getty Images
Fueling the Flames
A fire tornado rises from burning peat on a farm in Bangor, U.K., in 2008.
Combustible, carbon-rich gases released by burning vegetation on the ground are fuel for most fire tornadoes, Forthofer said. "The vegetation on the ground heats up enough to release gas, but some of the gas can't combust, because it doesn't have enough oxygen around it."
When sucked up by a whirl of air, this unburned gas travels up the core until it reaches a region where there is enough fresh, heated oxygen to set it ablaze. That's why the flames in a fire tornado's core look so tall and skinny, Forthofer said.
"The [gases] can't burn until they mix with enough oxygen, and that might not happen until way up above the ground."
Photograph by Simon Gray, My Shot
Finger of Fire
Visitors watch an artificial fire tornado created by several air-jet ventilators at the Phaeno Science Center in Wolfsburg, Germany, in August 2007.