Postfire debris flow hazards—Tips to keep you safe

Abstract

Often referred to as “mudflows,” debris flows are a type of landslide made up of a rapidly moving mixture of dirt, rocks, trees, and water (and sometimes ash) that start on a hillside and travel downvalley. They can easily overflow channels and severely damage houses, vehicles, or other structures. Areas burned by wildfires are especially susceptible to these hazards, which can be triggered by storms occurring days to years after a fire. Debris flows in burned areas can start on a dry slope after only a few minutes of heavy rainfall—about half an inch an hour or more. They can also threaten unsuspecting areas downstream, as debris flows can travel many miles and affect places that were neither burned nor received any rain. The tips provided in this Fact Sheet can help to keep you safe in a potential debris flow danger area.