Fire tornadoes, often depicted dramatically, are real phenomena. These swirling columns of flame form under specific environmental conditions during intense fires. Understanding their science helps demystify their existence and power.
Understanding Fire Tornadoes
A fire tornado, more accurately termed a fire whirl, is a spinning column of flame and ash induced by a fire. These phenomena are distinct from meteorological tornadoes, which descend from storm clouds. Fire whirls begin with swirling air, often made visible by smoke, forming when intense heat and turbulent wind conditions interact to form whirling eddies. Unlike traditional tornadoes, a fire whirl’s rotation comes from temperature-induced lifting and surface winds. While the public often uses “fire tornado,” scientists reserve it for the rarest, most intense fire vortices that exhibit true tornado-like characteristics, sometimes connecting to pyrocumulonimbus clouds.
The Science of Formation
Fire whirls form under specific conditions: an intense heat source, an unstable atmosphere, and wind patterns that introduce rotation. Intense heat from a fire causes the air above it to rise rapidly. This superheated air is less dense, creating a strong updraft, similar to a chimney effect. As hot air ascends, it forms a low-pressure zone, drawing in cooler air.
If this updraft encounters variable wind directions or uneven terrain, the rising air begins to spin. This shearing of winds introduces rotation into the air column. As the rotating column stretches vertically, it intensifies, much like a figure skater pulling in their arms to spin faster, due to angular momentum conservation. The vortex then draws in flames, smoke, and burning debris, becoming a visible, fiery column.
Real-World Occurrences and Characteristics
Fire whirls have been observed in various settings, from small bonfires to large-scale wildfires and industrial conflagrations. Most fire whirls are relatively small, typically 10 to 50 meters (33 to 164 feet) tall and a few meters wide, lasting only a few minutes. These smaller whirls often appear during intense wildfire events, especially when temperatures are high and vegetation is dry.
However, some fire whirls can grow to much larger, more destructive proportions. Exceptional cases have been recorded at over 1 kilometer (0.6 miles) tall, with wind speeds exceeding 200 kilometers per hour (120 mph), and persisting for more than 20 minutes. The Carr Fire in California in 2018 produced a devastating fire tornado, classified as an EF-3 on the Enhanced Fujita Scale, with estimated wind speeds of 143 mph and a rotating column reaching up to 17,000 feet. These larger phenomena can uproot trees 15 meters or taller and hurl burning embers, aiding rapid fire spread by igniting new blazes far from the main fire line.