The fire's second act.

Four months after the La Tuna Fire was declared contained, the first serious winter storm of 2018 rolled over Southern California. On Tuesday, January 9, the rain hit the fire-denuded slopes above the canyon and the hillsides gave way. Debris flows three feet deep poured down La Tuna Canyon Road. The fire was technically out, but it was not, in the way that matters, over.

Why a burned hillside becomes a river

Chaparral burns hot. After a fire like La Tuna, the topsoil can develop a hydrophobic layer — a thin crust of heat-baked organic compounds that repels water rather than absorbing it. Rain that would normally soak into the ground instead runs off the surface, carrying loose ash, gravel, scorched root mass, and everything else the fire loosened. On a 40-degree slope, the mixture accelerates. By the time it reaches the road below, it is moving fast enough to roll cars and strong enough to snap utility poles.

That is the conventional model. The less-conventional part, with the La Tuna Fire burn scar, is that the steep canyons of the Verdugo Mountains are extremely efficient at converting hillside debris into channelized flow. The side canyons of La Tuna Canyon Road function as natural sluices. Between September 2017 and the first January rains of 2018, Los Angeles County Public Works had identified roughly 300 Sun Valley homes that were at risk, and crews had been excavating debris basins above those homes, installing K-rails, and visiting residents to explain evacuation plans.

January 9, 2018

The first major storm of the water year arrived on Monday, January 8, and by the small hours of Tuesday morning it was dropping a sustained inch per hour on the burn scar. Mandatory evacuations had been issued the previous day for around 1,000 homes in the La Tuna Fire footprint. An additional 23 specific homes between 8300 and 8800 La Tuna Canyon Road — the stretch immediately downslope of the steepest burned drainages — were placed under narrow-band evacuation orders.

Around midday on Tuesday, the hillsides let go. La Tuna Canyon Road was buried in roughly three feet of debris at the peak of the flow, between Sunland Boulevard and the 210 Freeway. On the Burbank side of the ridge, a fast-moving river of mud came down Country Club Drive, sweeping away vehicles, trees, and utility poles, and rupturing a natural gas pipeline when a swept vehicle struck it. Forty to forty-five homes in that neighborhood were damaged.

"As you go up La Tuna Canyon, closer to the 210 Freeway, we've got about 36 inches deep of debris that came down from hillsides." — LAFD Battalion Chief Jamie Moore

Residents who stayed

Not everyone evacuated. Despite mandatory orders, a family of six chose to shelter in place at an address on the 8300 block of La Tuna Canyon Road. Their home was washed out; they became stranded. They were rescued after the water receded. No one in the canyon died in the January 9 flow — a combination of luck, preparation, and the fact that mudflows, for all their violence, move a little more slowly than wildfire and give people slightly more time to react.

LAFD crews launched drones to assess the hillsides above the neighborhood, on the reasonable theory that sending human crews up an unstable slope in active rain was a bad idea. Utility crews worked through the night in Burbank to restore power, gas, and water to approximately 40 homes on Country Club Drive. About two-thirds of those families chose to shelter in place through the disruption rather than go to the evacuation shelter at Sun Valley Recreation Center.

The long tail

The January 9, 2018 event was the worst of the post-fire mudflows, but not the only one. Additional debris flows and road closures hit La Tuna Canyon Road during the storms of March 2018 and again in December 2018. Each time, the same stretch between Sunland Boulevard and the 210 had to be bulldozed clear. Each time, voluntary or mandatory evacuation orders were issued for the vulnerable stretch, and each time a subset of residents chose to stay.

The hillsides took roughly three winters to re-vegetate enough that a normal storm would no longer trigger a debris flow. Even now, after major rain events, LA County Public Works occasionally issues a "Phase 2 debris flow forecast" for the old Land Fire burn area above the canyon, covering a specific box of streets between Horse Haven Street (north), Martindale Avenue (east), Penrose Street (south), and Ledge Avenue (west).