Video: What is a fire tornado?
A fire tornado has swept through the Brazilian city of Aractuba after a three-month drought created perfect conditions for the rare phenomenon.
The rare event occurs when a fire is whipped up by strong, dry air currents to form a vertical whirl.
They can consist of a whirlwind of hot air around or within the flames or a vortex of fire itself.
Also known as “fire devils” or “fire whirls”, they can uproot trees up to 49 ft (15m).
Fire tornadoes are usually 30-200ft (10-50m) and a few meters wide, and last only a few minutes.
But some of the largest can be more than a half a mile tall, contain winds over 100mph, and persist for more than 20 minutes.
Most large fire tornadoes are formed when wildfire converges with a warm updraft of air, and a wildfires can contain a number of fire whirls of varying intensity, size and duration.
An extreme example is the 1923 Great Kant? earthquake in Japan which ignited a city-sized firestorm and produced an enormous fire whirl that killed 38,000 people in fifteen minutes.
A rash of large fire whirls developed after lightning struck an oil storage facility near San Luis Obispo, California on April 7, 1926, killing two.
Thousands of whirlwinds were produced by the four-day-long firestorm – the larger of which carried debris 3 miles away.