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Ekstrom Library

Government Resources: Public Safety: Landslides

What is a Landslide?

The term landslide includes a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity acting on an over-steepened slope is the primary reason for a landslide, there are other contributing factors:

•erosion by rivers, glaciers, or ocean waves create oversteepened slopes

•rock and soil slopes are weakened through saturation by snowmelt or heavy rains

•earthquakes create stresses that make weak slopes fail

•earthquakes of magnitude 4.0 and greater have been known to trigger landslides

•volcanic eruptions produce loose ash deposits, heavy rain, and debris flows

•excess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures

Slope material that become saturated with water may develop a debris flow or mud flow. The resulting slurry of rock and mud may pick up trees, houses, and cars, thus blocking bridges and tributaries causing flooding along its path.  Source: USGS

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