FAQ's about Landslides

A landslide is defined as, the movement of a mass of rock, debris, or earth down a slope. (Cruden, 1991). 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 events such as rock falls, topples, slides, spreads, and flows (Varnes, 1996). Landslides can be initiated by rainfall, earthquakes, volcanic activity, changes in groundwater, disturbance and change of a slope by man-made construction activities, or any combination of these factors. Landslides can also occur underwater, causing tidal waves and damage to coastal areas. These landslides are called submarine landslides.

Failure of a slope occurs when the force that is pulling the slope downward (gravity) exceeds the strength of the earth materials that compose the slope. They can move slowly, (millimeters per year) or can move quickly and disastrously, as is the case with debris-flows. Debris-flows can travel down a hillside of speeds up to 200 miles per hour (more commonly, 30 – 50 miles per hour), depending on the slope angle, water content, and type of earth and debris in the flow. These flows are initiated by heavy, usually sustained, periods of rainfall, but sometimes can happen as a result of short bursts of concentrated rainfall in susceptible areas. Burned areas charred by wildfires are particularly susceptible to debris flows, given certain soil characteristics and slope conditions. More information can be found in USGS Fact Sheet numbers FS-071-00, Landslide Hazards (English Version), and FS-072-00, Peligros de Deslizamientos (Spanish Version).

Information on debris flows can be found in our Publications section.

Sources of Information for this FAQ:

(1). Cruden, D.M., 1991. A Simple Definition of a Landslide. Bulletin of the
International Association of Engineering Geology, No. 43, pp. 27-29.

(2). Varnes, D.J., 1996. Landslide Types and Processes, in Turner, A. K., and R.L. Schuster, Landslides: Investigation and Mitigation, Transportation Research Board Special Report 247, National Research Council, Wasington, D.C.: National Academy Press.

Go to the Natural Hazards Gateway, which includes:

• Earthquakes
• Floods
• Geomagnetism (solar flares, etc.)
• Hurricanes
• Landslides
• Seismic Zone Mapping
• Sinkholes
• Tsunamis
• Volcanoes
• Wildfires

Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. Liquefaction occurring beneath buildings and other structures can cause major damage during earthquakes. For example, the 1964 Niigata earthquake caused widespread liquefaction in Niigata, Japan which destroyed many buildings. Also, during the 1989 Loma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco.

For further information, see:

Earthquake Effects FAQ section
Soil Liquefaction Website - Univ. of Washington
California Geological Survey Seismic Hazards Maps

Although Mount Rainier (Washington) has not produced a significant eruption in the past 500 years, it is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Mount Rainier has 26 glaciers containing more than five times as much snow and ice as all the other Cascade volcanoes combined. If only a small part of this ice were melted by volcanic activity, it would yield enough water to trigger enormous lahars. Mount Rainier's potential for generating destructive mudflows is enhanced by its great height above surrounding valleys. -- From: Scott, et.al., 1990, Sedimentology, Behavior, and Hazards of Debris Flows at Mount Rainier, Washington: USGS Open-File Report 90-385, and Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.

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 km³.

The world's biggest prehistoric landslide, discovered so far, is in southwestern Iran, and is named the Saidmarreh landslide. The landslide is located on the Kabir Kuh anticline in Southwest Iran at 33 degrees N, 47.65 degrees E. The landslide has a volume of about 20 cubic kilometers, a depth of 300 m, a travel distance of 14 km and a width of 5 km. This means that about 50 billion tons of rock moved in this single event! For a current aerial view of the landslide, please see: http://daveslandslideblog.blogspot.com/2009/07/landslide-of-them-all-saidmareh-iran.html

• Please see the USGS Cascades Volcano Observatory website for more information on Mount St. Helens and other volcanoes: http://vulcan.wr.usgs.gov/home.html
• Schuster, Robert L., and Lynn M. Highland, 2001, Socioeconomic Impacts of Landslides in the Western Hemisphere, U.S. Geological Survey Open-file Report 01-9276. This publication is available on the web: http://pubs.usgs.gov/of/2001/ofr-01-0276/
• Harrison, J. V., and Falcon, N.L., 1938, An Ancient Landslip at Saidmarreh in Southwestern Iran, The Journal of Geology, Vol. 46, No. 3, Part I (Apr. - May, 1938), pp. 296-309 (article consists of 14 pages), The University of Chicago Press Stable URL: http://www.jstor.org/stable/30081302

Tsunamis are large, potentially destructive sea waves, most of which are formed as a result of submarine earthquakes, but which 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 earthquakes. Environmental damage by these tsunamis include coral reef destruction, contamination of wells and other sources of fresh water by salt water, denudation of trees and other types of dry-land vegetation, accelerated beach erosion, and fish and other marine life fatalities due to abnormal wave action. The flooding and powerful wave action of the tsunami may potentially cause damage to man-made containment vessels of petroleum products, chemicals, and garbage landfills, resulting in toxic leakage, which in turn has the potential to pollute both coastal land and ocean environment.

Tsunami waves can be generated from displacements of water resulting from rock falls, icefalls and sudden submarine landslides or slumps. Major earthquakes are suspected to cause many underwater landslides, which may contribute significantly to tsunami generation. For example, many scientists believe that the 1998 tsunami, which killed thousands of people and destroyed coastal villages along the northern coast of Papua-New Guinea, was generated by a large underwater slump of sediments, triggered by an earthquake.

The 1964 Alaska earthquake caused 115 deaths in Alaska alone, with 106 of those due to tsunamis generated by tectonic uplift of the sea floor, and by localized subareal and submarine landslides. The earthquake shaking caused at least 5 local slide-generated tsunamis within minutes after the shaking began. For an eyewitness account of the tsunami caused by the movement and landslides of the 1964 Alaska earthquake, please see: http://www.npr.org/templates/story/story.php?storyId=5007860

Current research in the Canary Islands concludes that there have been at least five massive volcano landslides that occurred in the past, and that these same large events may occur in the future. These giant landslides have the potential of generating large tsunami waves, at close and also very great distances and would have the potential to devastate large areas of coastal land, as far away as the eastern seaboard of North America.

Rock falls and rock avalanches in coastal inlets, such as those that have occurred in the past at Tidal Inlet, Glacier Bay National Park, Alaska have the potential to cause regional tsunamis that pose a hazard to coastal ecosystems and human settlements. On July 9, 1958, a magnitude M 7.9 earthquake on the Fairweather Fault triggered a rock avalanche at the head of Lituya Bay, Alaska. The landslide generated a wave that ran up 524 m on the opposite shore and sent a 30-m high wave through Lituya Bay, sinking two of three fishing boats and killing two persons.

Source of Information:

Geist, E. L., 1998, Source characteristics of the July 17, 1998 Papua New Guinea tsunami: EOS, Transactions of the American Geophysical Union, v. 79 (supplement), p. 571.

Committee on the Alaska Earthquake of Division of Earth Sciences, National Research Council, Seismology and Geodesy, 1972,Plafker, George, USGS, U.S. Geological Survey Professional Paper. 543-I. Tectonics of the March 27, 1964, Alaska Earthquake.

Siebert, Lee, 2004, Landslides resulting from structural failure of volcanoes, Catastrophic Landslides:  Effects, Occurrence and mechanisms, Evans, Stephen G., and Jerome V. DeGraff, eds., Reviews in Engineering Geology, Volume XV, Geological Society of America, Boulder, Colorado USA.

Wieczorek, Gerald F., Jakob, Matthias, Motyka, Roman, Zirnheld, Sandra L., and Patricia Craw, 2003, Preliminary assessment of landslide-induced wave hazards:  Tidal Inlet, Glacier Bay National Park, Alaska, U.S. Geological Survey Open-file report 03-100.

A landslide hazard map indicates the possibility of landslides occurring throughout a given area. A hazard map 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 thresholds, slope angle, soil type, and levels of earthquake shaking. An ideal landslide hazard map shows not only the chances that a landslide may form at a particular place, but also the chance that it may travel downslope a given distance.

The Thistle, Utah, landslide cost in excess of $200 million dollars (1984 dollars) to fix. The landslide occurred during the spring of 1983, when unseasonably warm weather caused rapid snowmelt to saturate the slope. The landslide destroyed the railroad tracks of the Denver and Rio Grande Western Railway Company, and the adjacent Highway 89. It also flowed across the Spanish Fork River, forming a dam. The impounded river water inundated the small town of Thistle. The inhabitants of the town of Thistle, directly upstream from the landslide, were evacuated as the lake began to flood the town, and within a day the town was completely covered with water. Populations downstream from the dam were at risk because of the possible overtopping of the landslide by the lake. This could cause a catastrophic outburst of the dam with a massive flood downstream. Eventually, a drain system was engineered to drain the lake and avert the potential disaster.

Eventually the Thistle landslide reached a state of equilibrium across the valley, but fears of reactivation caused the railway to construct a tunnel through the bedrock around the slide zone at a cost of a million dollars. Also, the highway had to be realigned around the landslide. When the lake caused by the landslide was drained, the residual sediment partially buried the town and virtually no one returned to Thistle. This landslide is still moving, at present, although at a fairly slow rate. State officials continue to monitor this landslide.

Source:

University of Utah, 1984, Flooding and Landslides in Utah—an Economic Impact Analysis, University of Utah Bureau of Economic and Business, Utah Dept. of Community and Economic Development, and Utah Office of Planning and Budget, Salt Lake City, Utah, 123 p.

Debris flows pose the greatest hazard to people near Mount Rainier .  A debris flow is a mixture of mud and rock debris that looks and behaves like flowing concrete. Giant debris flows sometimes develop when large masses of weak, water-saturated rock slide from the volcano's flanks. Many of these debris flows cannot be predicted and may even occur independently of a volcanic eruption. Giant debris flows can also form during an eruption as hot rock fragments tumble down the volcano's slopes, eroding and melting snow and glacier ice. Although they happen infrequently, giant debris flows have the potential to inundate much of the southern Puget Sound lowland. Scientists estimate that debris flows can travel the distance between Mount Rainier and the Puget Sound lowland in as little as 30 minutes to a few hours. About 100,000 people now live in areas that have been buried by debris flows during the past few thousand years. -- From: Walder and Driedger, 1995, Living With a Volcano in Your Backyard - Volcanic Hazards at Mount Rainier: USGS Open-File Report 95-421.

Before May 18, 1980, Mount St. Helens' summit altitude of 9,677 feet made it only the fifth highest peak in Washington State. It stood out handsomely, however, from surrounding hills because it rose thousands of feet above them and had a perennial cover of ice and snow. The peak rose more than 5,000 feet above its base, where the lower flanks merge with adjacent ridges. On May 18, 1980, the volcano lost an estimated 3.4 billion cubic yards (0.63 cubic mile) of its cone (about 1,300 feet in height), leaving behind a horseshoe-shaped crater (open to the north), with the highest part of the crater rim on the southwestern side being at 8,365 feet elevation. -- From: Foxworthy and Hill, 1982, Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days: USGS Professional Paper 1249.

Yes.  The list is at: "Major Catastrophic Landslides of the 20th Century"

This type of maps ranks slope stability of an area into categories that range from stable to unstable. Susceptibility maps show where landslides may form. Many susceptibility maps use a color scheme that relates warm colors (red, orange, and yellow) to unstable and marginally unstable areas and cool colors (blue and green) to stable areas.

During the past 10,000 years, about 60 giant debris flows from Mount Rainier have filled river valleys to a depth of hundreds of feet near the volcano, and have buried the land surface under many feet of mud and rock sixty miles downstream. Seven debris flows large enough to reach Puget Sound have occurred in the past 6,000 years. -- From: Walder and Driedger, 1995, Living With a Volcano in Your Backyard - Volcanic Hazards at Mount Rainier: USGS Open-File Report 95-421.

This type of map shows the expected annual cost of landslide damage throughout an area. Risk maps combine the probability information from a landslide hazard map with an analysis of all possible consequences (property damage, casualties, and loss of service).

Yes - USGS Circular 1325, "The Landslide Handbook - A Guide to Understanding Landslides", by Lynn Highland of the U.S. Geological Survey and Peter Bobrowsky of the Geological Survey of Canada. It is a resource to acquire knowledge about the geologic and climatic conditions which affect neighborhoods and communities.

A wide variety of additional information is available at "Links to More USGS Landslide Research and Information."

Each of our 50 states has a State Geological Survey. Most State Surveys have some landslide information. A link to your State Survey can be found on our website, http://geohazards.cr.usgs.gov, or by accessing: http://www.stategeologists.org/.

Also, your City and/or County may have a public works engineer and/or a geologist on staff, who would be best able to answer questions about landslides in your local area.

In the United States, it is estimated that the total dollar losses from landslides is between one and two billion dollars ($1.6 billion and $3.2 billion, year 2000 dollars). This figure is a conservative estimate, as there is no uniform method or overall agency that keeps track of or reports landslide losses. Landslides result in extremely high monetary losses in other countries, but there is no overall estimate as to the exact amount. The El Niño event in the San Francisco Bay Area caused landslide damage estimated to total approximately $140.9 million (1998 dollars; $154.4 million in 2003 dollars).

Sources of Information for FAQ #3:

• Committee on Ground Failure Hazards (1985) Reducing Losses from Landslides In the U.S., Commission on Engineering and Technological Systems, National Research Council, Washington, D.C., 41 p.
• Highland, Lynn M., Godt, Jonathan, Howell, David, and William Z. Savage (1998) U.S. Geological Survey Fact Sheet 089-98.

The most recent eruptive activity occurred at Lassen Peak (California) in 1914-1917 A.D. This eruptive episode began on May 30, 1914, when a small phreatic eruption occurred at a new vent near the summit of the peak. More than 150 explosions of various sizes occurred during the following year. By mid-May 1915, the eruption changed in character; lava appeared in the summit crater and subsequently flowed about 100 meters over the west and probably over the east crater walls. Disruption of the sticky lava on the upper east side of Lassen Peak on May 19 resulted in an avalanche of hot rock onto a snowfield. A lahar was generated that reached more than 18 kilometers down Lost Creek. On May 22, an explosive eruption produced a pyroclastic flow that devastated an area as far as 6 kilometers northeast of the summit. The eruption also generated lahars that traveled more than 20 kilometers down Lost Creek and floods that went down Hat Creek. A vertical eruption column resulting from the pyroclastic eruption rose to an altitude of more than 9 kilometers above the vent and deposited a lobe of pumiceous tephra that can be traced as far as 30 kilometers to the east-northeast. The fall of fine ash was reported as far away as Elko Nevada, more than 500 kilometers east of Lassen Peak. Intermittent eruptions of variable intensity continued until about the middle of 1917. -- From: Hoblitt, et.al., 1987, Volcanic Hazards with Regard to Siting Nuclear-Power Plants in the Pacific Northwest: USGS Open-File Report 87-297

Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by ground water circulating through them. As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces just get too big. If there is not enough support for the land above the spaces then a sudden collapse of the land surface can occur. These collapses can be small, as the picture below shows, or they can be huge and can occur where a house or road is on top.

The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. The picture below shows a sinkhole that quickly opened up in Florida, damaging a swimming pool, a road, and buildings.