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What is a landslide, and what causes them?

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Hello and welcome to CoreFacts, where we're always short on time and big on science. I'm Steve Sobieszczyk. Today we're going to be discussing landslides.

What is a landslide, and what causes them?

A landslide is defined as the movement 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 events such as rock falls, topples, slides, spreads, and flows. 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 also occur underwater, causing tsunamis that damage coastal areas. These landslides are called submarine landslides.

A landslide occurs when the force of gravity exceeds the strength of the earth materials that compose the slope. They can move slowly, (millimeters or inches per year) or can move quickly and disastrously, as is the case with debris-flows. Debris-flows can travel down a hillside of speeds of about 200 miles per hour (but 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.

And now you know. Join us every weekday for a new CoreFact. If you have a question you think we should answer on the air, email it to us at corefacts@usgs.gov or leave us a voicemail at 703-648-5600; long distance fees do apply.

The USGS CoreFacts is a product of the U.S. Geological Survey, Department of the Interior.

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Title: What is a landslide, and what causes them?

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Date Recorded: 4/24/2008


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