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 subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types.

Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope (mainly due to gravity) exceed the strength of the earth materials that compose the slope. Causes include factors that increase the effects of down-slope forces and factors that contribute to low or reduced strength. Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors. Earthquake shaking and other factors can also induce landslides underwater. These landslides are called submarine landslides. Submarine landslides sometimes cause tsunamis that damage coastal areas. 

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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

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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 may also result from the eruption or collapse of island or coastal volcanoes and the formation of giant landslides on marine margins. These landslides, in turn, are often triggered by

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Under what circumstances do U.S. Geological Survey landslide personnel conduct field work in landslide prone areas?

USGS landslide researchers have ongoing field projects in several areas of the U.S., including parts of the Pacific coastal ranges, Rocky Mountains, and the Appalachians. USGS scientists also respond to major landslide events, including some that result in federally-declared disasters, and in some cases, foreign countries

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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,

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What is a landslide hazard map?

Several kinds of maps are used to depict danger from landslides. These maps may be as simple as a map that uses the locations of old landslides to indicate potential instability, or as complex as a quantitative map incorporating probabilities based on variables such as rainfall, slope angle, soil type, and levels of

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Is there a list of the largest landslides in the world?

See the list of  worldwide catastrophic landslides of the 20th century.

The five largest Worldwide Landslides are:

  • 1911 - Tadzhik Republic - 2,000,000,000 cubic meters of material - 54 killed
  • 1919 - Indonesia - 185 square kilometers of
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What was the biggest landslide in the world?

The world's biggest historic landslide occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington, USA. The volume of material was 2.8 cubic kilometers (km).

The world's biggest prehistoric landslide, discovered so far on land, is in southwestern Iran,

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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

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When does the U.S. Geological Survey issue a landslide advisory, and under what conditions?

The U.S. Geological Survey derives its leadership role in landslide hazard-related work from the Disaster Relief Act of 1974 (the Stafford Act). The Director of the USGS has been delegated the responsibility to issue warnings for an earthquake, volcanic eruption, landslide, or other geologic catastrophe (1974 Disaster

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How many deaths result from landslides each year?

An average of between 25 and 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 fall, debris-flows, or volcanic debris flows (called lahars). Debris flows occurring in December, 2003, killed 16

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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, of poorly planned alteration of drainage patterns, and of disturbing old landslides

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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

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Date published: July 20, 2017

Landslide Assistance from the Air

The USGS uses cutting edge technologies to investigate and forecast landslides and other natural hazards.

Date published: July 11, 2017

Huge landslide on California’s Big Sur coast continues to change

The Mud Creek landslide on California’s Big Sur coast keeps eroding.

Date published: June 1, 2017

USGS maps, measures huge landslide on California's Big Sur coast

USGS scientists analyzing before-and-after air photos have calculated the size of the May 20 landslide on California’s Big Sur coast, about 140 miles south of San Francisco. 

Date published: September 16, 2016

EarthView–Landslide Spreads 6 Miles Across Glacier Bay National Park

Two snapshots from Landsat show the extent of a landslide in an Alaska National Park.

Date published: October 3, 1997

El Nino May Trigger Landslides... USGS Map Indicates Susceptibility and Incidence of Landslides

Floods, coastal erosion and heavy precipitation aren’t the only predicted consequences of the El Nino phenomena. Landslides and debris flows could happen in areas where intense rainfall occurs.

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Big Sur landslide on May 20, 2017 showing material across Highway 1.
May 27, 2017

USGS air photo of the Mud Creek landslide, taken on May 27, 2017.

Big Sur Landslide fly around animation
May 27, 2017

Big Sur Landslide fly around from May 27, 2017, a preliminary computer animation. The slide created roughly 13 acres of new California land. 

2014 Landslide in Washington State
January 4, 2017

Photograph from aerial survey showing the upper parts of the 2014 landslide in northwest Washington. Photograph credit: Jonathan Godt, USGS

New Zealand Landslides
2016 (approx.)

Photograph showing landslides covering State Route 1 near Ohau Point. The route was impacted my several landslides and is the main north-south highway on the eastern part of the South Island of New Zealand.

As many as 80,000 landslides occurred as the result of a magnitude 7.8 earthquake in New Zealand in November of 2016. The earthquake and landslides caused casualties and significant damage to communities, including homes and transportation infrastructure. The USGS is working with New Zealand’s GNS Science in assessing the area's stability and potential impacts of landslide dams blocking stream channels in this mountainous region. Understanding the factors that contributed to the severity and extent will improve and inform the development of models and near-real-time hazard assessments. An example is USGS PAGER, which provides fatality and economic loss impact estimates following significant earthquakes worldwide. These events provide a reference for domestic earthquakes in mountainous regions, such as southern California. Scientists will also use this as an opportunity to observe how landslide dams behave, ranging from impacts on downstream flooding to sediment accumulation over the next several years.

Image: 2005 Landslide in Conchita, CA
March 14, 2016

This landslide occurred at La Conchita, California in 2005. Ten people were killed.

Oso landslide. Huge swath of mountain missing.
2014 (approx.)

Oso landslide 2014

May 9, 2012

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 Universite Paris, makes clear the destructive power of these flows.

A person looking across the valley using a laser scanning the entire Cleveland Corral landslide.
2010 (approx.)

Laser scanning the entire Cleveland Corral landslide from across the valley during an active spring (2010).  Repeat scans are used to detect movement throughout the slide.

USGS
April 23, 2008

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depiction of the mechanics of a landslide
November 30, 2000

graphic illustration of the parts of a landslide

Aerial view of the Mill Creek landslide blocking Highway 50.
January 24, 1997

Photo 1: Aerial view of the Mill Creek landslide blocking Highway 50.