Landslide is the movement of rock, soil and debris down a hillside or slope. Landslides take lives, destroy homes, businesses, and public buildings, interrupt transportation, undermine bridges, derail train cars, cover marine habitat, and damage utilities.
The term landslide includes a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Ground failures that result in landslides occur when gravity overcomes the strength of a slope. While gravity is the primary reason for a landslide, there can be other contributing factors, including the following:
- Saturation, by snowmelt or heavy rains, that weaken rock or soils on slopes.
- Erosion by rivers, glaciers, or ocean waves that create over-steepened slopes.
- Topography of a slope – its shape, size, degree of slope and drainage.
- Stress from earthquakes magnitude 4.0 and greater can cause weak slopes to fail.
- Volcanic eruptions that produce loose ash deposits and debris flows.
- Excess weight, from accumulation of rain or snow, from stockpiling of rock or ore, from waste piles, or from manmade structures, may stress weak slopes to failure.
- Human action, such as construction, logging or road building that disturbs soils and slopes.
Idaho’s geology, landscape, climate, soils, and other factors are locally conducive to landslide activity and numerous landslides occur each year in Idaho. Significant landslide events that have resulted in disasters are rare, but several have been recorded in the state. Recent history has shown that since 1990 landslides have resulted in two Federally Declared Disasters and four State Disasters.