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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.
Under what circumstances do U.S. Geological Survey landslide personnel conduct field work in landslide-prone areas?
The Mud Creek landslide on California’s Big Sur coast keeps eroding.
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.
Two snapshots from Landsat show the extent of a landslide in an Alaska National Park.
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.
Photograph from aerial survey showing the upper parts of the 2014 landslide in northwest Washington. Photograph credit: Jonathan Godt, USGS
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...
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...
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.
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