Thursday, May 08, 2014

Fire Breathing Dust Devil Toys with Tumbleweeds

Combine a firestorm with some tumbleweeds and a dust devil and you get a massive vortex that’s unlike anything you’ve seen before. Watch as fire experts in Rocky Mountain, Arkansas come face-to-face with a smoky, debris-littered dust devil moving across a burning field.

Dust devils are not nearly as powerful or destructive as tornados, but that does not stop the cautious men in the video from keeping their distance. Dust devils form when hot air near the ground finds a section of low-pressure cool air above it. When this happens, the hot air quickly rises and under certain conditions it can start to rotate, forming a vertical column.

Usually, the air near the surface heats up due to radiation from the Sun. But it looks like what happened in this scenario is that the heat from the controlled fire initiated the vortex. And as the dust devil grew, it began collecting nearby tumbleweeds in the process – the large, black, floating clumps.

The more mass the dust devil picks up, the more that moves to the center of the vortex. As a result, the dust devil’s rotation velocity intensifies because angular momentum is conserved.

About 3 minutes into the video, the dust devil sweeps the fire up into its funnel. As a result, you get an example of what’s called a fire tornado. Fire can reach significantly greater heights when it is in a vertical, rotating funnel than it ever could on its own. This is because there is an updraft inside the column that coaxes the flames skyward.

Like dust devils, tornadoes can manipulate fire in a similar way. Because tornadoes are often more powerful than dust devils, real fire tornadoes are an incredible spectacle to behold. Here is one example:

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