The sudden downslope movement of rock, soil and debris under the force of gravity, triggered when a slope's material can no longer resist gravity's pull, commonly following heavy rainfall, an earthquake, volcanic activity or human alteration of a hillside. Landslides range from a slow, barely perceptible creep to a catastrophic, fast-moving collapse capable of burying entire communities within seconds, and they are among the most geographically widespread natural hazards, occurring on any sufficiently steep slope where the underlying material becomes unstable.
Facts
PeriodicityNot seasonal but event-triggered, commonly initiated by rainfall, snowmelt, changes in water level, stream erosion, changes in groundwater, earthquakes, volcanic activity or human disturbance. 2 ScaleThe largest landslide in Earth's recorded history on land occurred with the 1980 eruption of Mount St. Helens, with a volume of 2.8 cubic kilometers that traveled about 22.5 kilometers. 2 First DescribedGeologist David Varnes proposed a tighter classification scheme for landslides and other mass movements in 1978. 1 Identification
Distinguishing AppearanceThe term landslide encompasses five modes of slope movement: falls, topples, slides, spreads and flows. 1 Connections
Associated With
Earthquake-triggered landslides are one of the most common and destructive secondary hazards of strong seismic shaking on steep or saturated slopes.
A landslide entering a body of water, especially a submarine or coastal slide, can directly generate a tsunami by displacing a large volume of water, as documented at Lituya Bay in 1958.
Sources
1. Landslide, Wikipedia
Types section
In 1978, geologist David Varnes noted this imprecise usage and proposed a new, much tighter scheme for the classification of mass movements.
Types section [distinguishing-appearance]
The term 'landslide' encompasses five modes of slope movement: falls, topples, slides, spreads, and flows.
View the Source2. USGS FAQ, What is a landslide and what causes one
What causes landslides section
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.
Largest landslide section
That landslide had a volume of 2.8 cubic kilometers (0.67 cubic miles) of material and the landslide traveled about 22.5 kilometers (14 miles) down the North Fork Toutle River.
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