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It sounds like the title of a straight-to-DVD disaster movie, but no, a "firenado" is one of nature's own spectacles – albeit with a little rebranding. As the name suggests, a firenado is what can happen when a tornado-like weather phenomenon meets a ground fire. The result: roaring spouts of flame shooting 100ft into the sky.
Firenadoes – or "fire whirls" as they used to be known – typically only flare up for a few minutes, which explains why they have been relatively obscure until now. But camera-wielding citizens have begun to catch them on film around the world, from Denver, Colorado to Aracatuba, Brazil. On Monday, Janae Copelin became an Instagram sensation with her snap of a firenado caused by crop-burning in Missouri. "This had to be the coolest/scariest thing I've ever seen," she wrote. In 2012, cameraman Chris Tangey captured one on video in the Australian outback, which became a global news item.
Outback firenado-Australia from chris tangey on Vimeo.
Reading this on mobile? Click here to view the video
The chances of a firenado are not as slim as they look, though. A raging bush fire can create its own tornado-like conditions. Vortices, from hurricanes to dust-devils, typically form when two different conditions of air meet and one rapidly moves towards the other. Usually it's warm, moist air meeting cold dry air in the atmosphere, but the intense heat of a bush fire can create enough of a differential all by itself. As well as the actual flames, the vortex sucks up combustible gases released by the fire, which meet oxygen-rich air in the centre of the vortex and ignite. The resultant heat fuels the vortex even further, producing a jet engine of an inferno.
A firenado in Denver, ColoradoReading this on mobile? Click here to view the video
The results can be spectacular, even without an Instagram filter, but amateur film-makers had better not get too close. Firenadoes can be fantastically destructive. They can reignite ashes and spread burning debris for miles, and generate huge and dangerous wind speeds. Investigations into a catastrophic bush fire in Canberra in 2003, for example, found a 25km-long strip running through the middle of the burnt area where trees had been snapped off and cars lifted off the ground. The fire had, in fact, created a 250km/h tornado.
The phenomenon is now being retrospectively ascribed to previous "firestorms", such as historic earthquakes, bush fires and even aerial bombings.
We could be seeing more firenadoes in the future, too, with climate change judged to be increasing the likelihood of extreme weather, including both tornadoes and fires. Perhaps that disaster-movie scenario isn't so far fetched.
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