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 potential hazards posed by landslides produced from burned watersheds.

Post-fire landslide hazards include fast-moving, highly destructive debris flows that can occur in the years immediately after wildfires in response to high intensity rainfall events, and those flows that are generated over longer time periods accompanied by root decay and loss of soil strength. Post-fire debris flows are particularly hazardous because they can occur with little warning, can exert great impulsive loads on objects in their paths, and can strip vegetation, block drainage ways, damage structures, and endanger human life. Wildfires could potentially result in the destabilization of pre-existing deep-seated landslides over long time periods.

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How do landslides cause tsunamis?

Tsunamis are large, potentially deadly and destructive sea waves, most of which are formed as a result of submarine earthquakes. They can also result from the eruption or collapse of island or coastal volcanoes and from giant landslides on marine margins. These landslides, in turn, are often triggered by earthquakes. Tsunamis can be generated on...

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...

Do human activities cause landslides?

Yes, in some cases human activities can be a contributing factor in causing landslides. Many human-caused landslides can be avoided or mitigated. They are commonly a result of building roads and structures without adequate grading of slopes, poorly planned alteration of drainage patterns, and disturbing old landslides. Detailed on-site...

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...

What is a landslide and what causes one?

A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct influence of gravity. The term "landslide" encompasses five modes of slope movement: falls, topples, slides, spreads, and flows. These are further...
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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: 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: September 13, 2019

Fast Fire Facts from USGS


You’ve got questions about USGS fire science. We’ve got answers.

Date published: May 27, 2017

USGS helping to monitor and assess huge Big Sur landslide

USGS is collecting and analyzing air photos to help monitor a huge landslide that occurred May 20 on California’s Big Sur coast.

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.

Date published: November 4, 2016

Imagery Reveals More Landslides in Western Columbia Gorge

New mapping in the western portion of the Columbia Gorge in Skamania County, Washington, shows previously unrecognized landslides beneath dense forest cover.

Date published: October 6, 2009

Debris Flows May Affect Southern California Communities

Rainstorms this year in the area burned by the Station Fire have the potential to trigger debris flows that may impact neighborhoods at the base of the San Gabriel Mountains as well as areas in Big Tujunga Canyon, Pacoima Canyon, Arroyo Seco, West Fork of the San Gabriel River, and Devils Canyon, according to an assessment released today by the U.S. Geological Survey.

Date published: November 7, 2007

NOAA, USGS Warning System to Help Protect Southern Californians from Debris Flows and Flash Floods

A debris flow and flash flood warning system developed jointly by NOAA's National Weather Service and the U.S. Geological Survey will help protect Southern Californians from potentially devastating debris flows-commonly known as mud slides- and flash floods in and around burn areas created by the recent wildfires.

Date published: December 30, 2004

Post-Fire Debris Flow Hazards Shown on New USGS Maps

The U.S. Geological Survey (USGS) has posted new maps on the Internet showing basins with the greatest potential for producing mudslides as a result of the devastating October fires in Southern California. 

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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
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

Image: Debris Flow Damage in California
February 8, 2010

Debris Flow Damage in California

House damaged by debris flows generated in Mullally Canyon in response to a rainstorm on February 6, 2010. The drainage basin above this home was burned the previous summer by the Station Fire, the largest fire in the history of Los Angeles County.

Attribution: Natural Hazards
Image: Debris Flow Damage
February 8, 2010

Debris Flow Damage

House engulfed by debris flows generated in response to a rainstorm on February 6, 2010. This house was west of Briar Wood Canyon in southern California. The small, but steep and rugged drainage basin above this home was burned the previous summer by the Station Fire, the largest fire in the history of Los Angeles County.

Attribution: Natural Hazards
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. 

January 24, 2010

Debris Flow Danger Follows Storms in Southern California

The powerful storms that swept through Southern California dumped a lot of rain in that region, leaving behind the danger of debris flows.

Sue Cannon, USGS research geologist, explains the hazardous situation facing residents in and near the San Gabriel Mountains, how people in the area can respond to these hazards, and what the USGS is doing to respond.

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.

USGS CoreCast
December 3, 2007

The Fire's Out, but Danger Remains: Post-Wildfire Debris Flows

After the smoke from wildfires clears, debris flows can become a big problem. USGS Research Geologist Sue Cannon talks about how.

Image: Debris Flow from 2006 Floods in Southern Arizona
September 1, 2006

Debris Flow from 2006 Floods in Southern Arizona

This photograph shows the snout of a debris flow that stopped in the channel of Rattlesnake Creek during the floods of July 31, 2006. This snout is several miles upstream from the confluence of Rattlesnake and Sabino Creeks, and the large boulders are typical of the largest particles transported during debris flows in the southern Santa Catalina Mountains. Most of these

Attribution: Natural Hazards
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.