Mudflow triggered by rain shuts down Pacific Coast Highway in Malibu area

Overnight rain led to mudflow on the Pacific Coast Highway, shutting down all lanes of the roadway between Malibu and the Santa Monica area Friday, authorities said. 

Forecasters had issued a flood advisory for that area of the coastline Thursday night, with National Weather Service Los Angeles warning of possible "mud flows and shallow debris flows" in areas left burn-scarred by the Palisades Fire. Caltrans officials said there was a slide in an area of the Pacific Coast Highway just north of Big Rock Drive in Malibu.

Lanes in both directions on the PCH were closed Friday morning between Carbon Beach Terrace in Malibu and Chautauqua Boulevard about 11 miles south, Caltrans said just before 9 a.m. The highway was just beginning to reopen after being fully closed for weeks due to the Palisades Fire and ongoing cleanup efforts. But rain forecasts led to more closures earlier this week. 

On Thursday night, rainfall measured 0.60 inches per hour in an area west of the Palisades Fire burn scar area. Drier conditions are expected this weekend through the beginning of next week, forecasters say.

Bulldozers had to remove about 10 truckloads of debris, Caltrans officials said, saying there was more debris drying out on the shoulder of the highway before being removed. The agency's geotechnical team is going to survey the closure area Friday to determine when the highway can reopen.

Video from overnight shows rain pouring down in the Pacific Palisades and nearby areas, mud dislodging from boulders along the PCH and spilling onto the roadway. With rain in the forecast this week, fears have arisen over possible mudslides and debris flows being triggered by the precipitation, particularly in areas where the fire left the terrain scorched barren. 

Crews led by Los Angeles County Public Works have been carrying out cleanup efforts and other preparations in recent weeks in areas burned by the Palisades and Eaton fires, working to clear out as much debris as possible before expected rainfall.

Debris flows are described by the National Weather Service as "fast-moving" landslides that can be potentially deadly, sometimes including what the agency calls "powerful mixtures of mud, rocks, boulders, entire trees," and sometimes, even vehicles or homes. 

"Debris flows occur most commonly during intense rain after wildfires," the National Weather Service reports. "A debris flow doesn't need a long rain or a saturated slope. It can start on a dry slope after only a few minutes of intense rain."