The Blue Cut fire is the latest conflagration burning up drought-ridden California, and it’s truly massive. About 60 miles northeast of Los Angeles, it roared to life quickly, starting out at a mere five acres on Tuesday and expanding into an inferno that has surprised seasoned firefighters with its intensity. So far, it has charred 35,969 acres of land, forced more than 82,000 people to evacuate their homes, and blocked off major transportation corridors. The fire is currently 22 percent contained.
Photos from the scene, like images of many a severe wildfire, look like the four horsemen rode up to the hills around San Bernardino and decided to torch the place. But some photographers and news outlets have noticed a particularly striking phenomenon blossoming on the blaze’s fringes: firenadoes. Or, as more sedate researchers call them, fire whirls. They’re spinning columns of smoke and fire, caused by flowing wind interacting with the blaze itself–a complex mix of fire and fluid dynamics that makes them devilishly hard to study in the field.
To get a fire whirl, you need two things: a spinning tube of air, and a way to stretch that tube. Air is constantly spinning–wind might blow along a mountainside and form eddies. Or the fire itself can heat a plume of air above it and pull cool air in at its base, forming a rotating system that lies parallel to the ground. Then, the spinning air gets pushed up into the sky as heat from the flames rises, stretching the tube and making it spin faster and faster as it turns vertical. Et voila: A spinning, incandescent pillar of flames.
Craig Clements is a fire meteorologist at San Jose State University, and he’s one of the only researchers who studies fire whirls in the wild. Whenever there’s a wildfire blazing in California, his team rushes out to get measurements, packing up their pickup truck and scanning burning areas with LiDAR to find out wind speeds and directions. “You have to be at the right place at the right time,” he says.
Awe-inspiring as they are, firenadoes are actually fairly common, Clements says. They appear everywhere from small grass fires to thousand-acre blazes like Blue Cut, and they vary widely in size and intensity. “They might be very small things, not even a foot across, to the whole smoke column itself,” says Janice Coen, a wildfire modeler at the University Corporation for Atmospheric Research.
But even if they’re not big, firefighters count firenadoes as extreme fire behavior, because they’re unpredictable. The whirling columns can suck in embers and fling them out–which could spread the fire faster and in unexpected directions. Big ones can tip over trucks, tear off roofs, and rip out trees. They can even detach from their mother fire and move independently, says Coen. A 2002 fire in Colorado produced a firenado that went rogue and traveled across a dry lake bed by itself.
So how do firefighters tackle them? Well, they don’t. Usually, their strategy is to avoid firenadoes once they appear, and turn their efforts to less active, more stable areas instead. Much of how fire whirls form depends on the way the wind is flowing in that particular area, affected by the terrain and the fire itself–both of which are rapidly evolving as firefighters attack the flames. “We see them all the time, but we can’t forecast where they’re going to go,” says Clements. So it’s safer to just stay away.
That strategy won’t change any time soon. Researchers understand the basic dynamics that power them, but most of what they know about fire whirls comes from lab experiments (generating mini, controlled firenadoes), or from modeling, says Clements. His team’s goal is to detect vortices of air forming in real time, so they can warn firefighters about them before they turn into maverick fire whirls. Because, well, you can’t beat the firenado.