Weather Words: Debris Flow

The West has been hammered with several atmospheric rivers in recent weeks, so it’s important to know terms such as debris flow. Debris flows are incredibly dangerous to life and property and occur after intense rainfall. This fast-moving rush of mud, rocks and debris quickly flow downhill and can sometimes come with little warning. They are many times triggered after an area has been burned from wildfires and the land isn’t anchored well by vegetation.

In August of 2020, The Cameron Peak Fire in Colorado quickly became the largest wildfire in Colorado history. It burned simultaneously with three other fires nearby that scorched more than 575 square miles of Colorado’s landscape that summer/fall. The following summer, July 2021, intense rainfall fell on the burned areas at rainfall rates up to 1-2 inches per hour. This resulted in several massive debris flows that destroyed several structures and resulted in four fatalities.

The National Weather Service and USGS operate a debris flow warning system that helps residents prepare for the possibility of debris flows. Make sure you are getting weather updates during rainy weather events that could possibly trigger debris flows.

J​ennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.