Multiple dust devils and fire whirls formed in the Burning Man bonfire last weekend. They grew to over 100 feet tall and drifted across the Black Rock Desert with rapidly whirling winds. They picked up debris and plowed through the burners downwind of the fire.

Over and over the fire birthed these dust devils — I counted at least a dozen in one video — and some of them were actually still on fire as they peeled away from the flames.

The weather needs to be pretty boring for this to work. Think clear skies and light wind. Dust devils form when a pocket of hot air rises rapidly through the cooler surrounding air. The velocity of this rising motion causes the air column to stretch vertically, and it begins to spin thanks to the conservation of angular momentum. This is the same reason figure skaters spin faster when they pull their arms in toward their bodies.

In this case, the bonfire heated the air around it and it rose rapidly, stretched and began to spin. A very light wind must have been present, since the whirls drifted away from the bonfire. In some cases, debris and ash were still on fire inside the whirl, which obviously poses a significant risk to the crowd downwind if they don’t get out of the way.