LA gets rain, but also risk of flooding and debris flows from wildfire burn scars – a geologist explains the threat
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Jen Pierce, Boise State University
(THE CONVERSATION) While firefighters work to extinguish the Los Angeles-area wildfires, city officials and emergency managers are also worried about what could come next.
Light rain began falling on Jan. 25, 2025, helping firefighters who have been battling fires for nearly three weeks, but rain can also trigger dangerous floods and debris flows on burned hillslopes. The National Weather Service issued a flood watch for the burned areas through Jan. 27.
Debris flows can move with the speed of a freight train, picking up or destroying anything in their path. They can move tons of sediment during a single storm, as Montecito, just up the coast from Los Angeles, saw in 2018.
What causes these debris flows, sometimes called mudflows, and why are they so common and dangerous after a fire? I am a geologist whose research focuses on pyrogeomorphology, which is how fire affects the land. Here’s what we know.
How debris flows begin
When...