HELENA — Despite the already active Horse Gulch wildfire, a peculiar event was observed in the burn scar recently.
What appeared to be a dark tornado was actually a dust devil, or as some may refer to it, a soot devil.
These swirling columns of dust are generated by intense surface heating and are typically smaller and less powerful than tornadoes, though sometimes they can be quite strong.
Dust devils can reach internal wind speeds of up to 100 mph, with diameters ranging from a few feet to as wide as 300 feet. They can reach heights of up to 500 to 1,000 feet, resembling tornadoes. A dust devil can persist for an hour or longer.
Despite their smaller size compared to tornadoes, dust devils can still cause damage by lifting dust and debris into the air. Strong dust devils have been known to damage or destroy small structures.
Dust devils form under conditions of strong surface heating, usually in clear skies and light winds that allow the ground to heat the air to temperatures significantly higher than the surrounding air.
The heated air near the surface rises rapidly, creating an updraft that leads to a spinning motion caused by a vacuum of air at the base.
This particular dust devil emerged over the hot, charred ash from the Horse Gulch fire, lifting soot several hundred feet into the air. Wind speeds in this event may have reached 40-50 mph.
