What is a debris flow?

Debris flows are fast-moving landslides that are particularly dangerous to life and property because they move quickly, destroy objects in their paths, and often strike without warning. They occur in a wide variety of environments throughout the world, including all 50 states and U.S. Territories. Debris flows generally occur during periods of intense rainfall or rapid snowmelt and usually start on hillsides or mountains. Debris flows can travel at speeds up to and exceeding 35 mph and can carry large items such as boulders, trees, and cars. If a debris flows enters a steep stream channel, they can travel for several miles, impacting areas unaware of the hazard. Areas recently burned by a forest fire are especially susceptible to debris flows, including the areas downslope and outside of the burned area. Debris flows are a type of landslide and are sometimes referred to as mudslides, mudflows, lahars, or debris avalanche.

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What should I know about wildfires and debris flows?

Wildland fires are inevitable in the western United States. Expansion of human development into forested areas has created a situation where wildfires can adversely affect lives and property, as can the flooding and landslides that occur in the aftermath of the fires. There is a need to develop tools and methods to identify and quantify the...

Can major landslides and debris flows happen in all areas of the U.S.?

Landslides can and do occur in every state and territory of the U.S.; however, the type, severity, and frequency of landslide activity varies from place to place, depending on the terrain, geology, and climate. Major storms have caused major or widespread landslides in Washington state, Oregon, California, Colorado, Idaho, Hawaii, Virginia, Ohio,...

What is the difference between a landslide advisory, a landslide watch, and a landslide warning?

An advisory is a general statement about the potential of landslide activity in a given region relative to developing rainfall predictions. An advisory may include general statements about rainfall conditions that can lead to debris-flow activity, and list precautions to be taken in the event of heavy rainfall. A watch means that landslide-...

How many deaths result from landslides each year?

An average of 25-50 people are killed by landslides each year in the United States. The worldwide death toll per year due to landslides is in the thousands. Most landslide fatalities are from rock falls, debris flows, or volcanic debris flows (called lahars). Twenty-three people were killed, at least 167 injured, and more than 400 homes were...

Why study landslides?

Landslides are a serious geologic hazard common to almost every State in the United States. As people move into new areas of hilly or mountainous terrain, it is important to understand the nature of their potential exposure to landslide hazards, and how cities, towns, and counties can plan for land-use, engineering of new construction and...
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Date published: January 7, 2021

Post-Wildfire Debris Flow Awareness

Post-wildfire hazards in Colorado can be as dangerous as the fires themselves.

Date published: February 6, 2020

New Landslide Guidebook for Puerto Rico Residents

A new landslide guidebook released February 5 is now available for Puerto Rico residents to learn more about the landslide hazards that can impact the island.

Date published: October 9, 2019

Landslide Risks Highlighted in New Online Tool

The U.S. Geological Survey today unveiled a new web-based interactive map that marks an important step toward mapping areas that could be at higher risk for future landslides. In collaboration with state geological surveys and other federal agencies, USGS has compiled much of the existing landslide data into a searchable, web-based interactive map called the U.S. Landslide Inventory Map.

Date published: January 5, 2017

Predicting Postfire Debris Flows Saves Lives

When wildfires spread and scorch the earth, people like Penny Luehring have to act fast. Secondary impacts such as debris flows can be devastating to nearby communities.

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October 25, 2018

PubTalk 10/2018 — Post-fire debris flow early warning

Title: Post-Fire Debris-Flow Early Warning: The case for forecast-based warning systems

  • Post-fire debris flows can initiate after only a few minutes of intense rain, and during the first storm following wildfire.
  • Early warning systems must provide sufficient time to make informed decisions and take reasonable preventative action.
  • If you're
Montecito after debris flow
January 14, 2018

Montecito after debris flow

The Dec. 4, 2017 Thomas fire, Southern California's largest wildfire on record, burned more than 280,000 acres across Ventura and Santa Barbara counties for nearly a month.

January 20, 2017

Post-wildfire debris flow: 2016 Fish Fire, Las Lomas Canyon

The June 2016 Fish Fire burned over 12 km^2 in Los Angeles County, California. After the fire, the USGS installed an automated rain-triggered camera to monitor post-wildfire flooding and debris flow in a small canyon above the Las Lomas debris basin in Duarte. This video shows the peak flow triggered by an intense rainstorm on January 20, 2017.
 

Predicting Postfire Debris Flows Saves Lives
January 4, 2017

Predicting Postfire Debris Flows Saves Lives

Predicting Postfire Debris Flows Saves Lives

July 19, 2015

Post-wildfire Flood and Debris Flow: 2014 Silverado Fire

In 2014, the Silverado Fire burned approximately 4 km^2 in Orange County, California. After the fire, the USGS installed an automated rain-triggered camera to monitor post-wildfire flooding and debris flow at the outlet of a small 0.6 km^2 basin within the burn area. This video shows the initial surge and peak flow triggered by an intense rainstorm on July 19, 2015. The

May 9, 2012

Volcano Web Shorts 2: Debris Flows

Debris flows are hazardous flows of rock, sediment and water that surge down mountain slopes and into adjacent valleys. Hydrologist Richard Iverson describes the nature of debris-flow research and explains how debris flow experiments are conducted at the USGS Debris Flow Flume, west of Eugene, Oregon. Spectacular debris flow footage, recorded by Franck Lavigne of the

Downstream impacts of a post-fire debris-flow in Mullally Canyon
February 6, 2010

LS Post Fire Debris Flow

Downstream impacts of a post-fire debris-flow in Mullally Canyon on February 6, 2010, near La Canada-Flintridge, California. Debris flow was generated during a burst of high-intensity rainfall over the area burned by the September 2009 Station Fire. 

Landslide monitoring station equipment with slight debris flow
December 31, 2009

Landslide monitoring equipment with debris flow

Debris-flow monitoring station at the Arroyo Seco monitoring site established after the 2009 Station Fire, CA.

video thumbnail: USGS and California Wildfires: Post Fire Debris Flow (part 2)
December 30, 2007

USGS and California Wildfires: Post Fire Debris Flow (part 2)

Jim Bowers, USGS, California Hydrologic Monitoring Program Chief talks about the potential for debris flows in central Orange County, Modjeska Canyon, as a result of the 2007 fires.

video thumbnail: USGS and California Wildfires: Post Fire Debris Flow (part 1)
December 30, 2007

USGS and California Wildfires: Post Fire Debris Flow (part 1)

Jim Bowers, USGS, California Hydrologic Monitoring Program Chief, talks about an historic streamflow site that was buried by debris flows as a result of the 2003 fires.

rocks, boulder, broken furniture, fallen trees, and other debris surround trees and cover the ground in Cable Canyon
January 9, 2004

Post-fire Debris Flow

Debris Flow in Cable Canyon following the 2003 Old Fire in the San Bernardino Mountains, California.

Comet Falls with the 2001 Van Trump Creek debris flow, which origin...
August 15, 2001

Comet Falls with the 2001 Van Trump Creek debris flow, which origin...

Comet Falls with the 2001 Van Trump Creek debris flow, which originated at Kautz Glacier on Mount Rainier, Washington.