Landslides occur when ground or rock slides by gravity. Landslide hazards are greatest in areas where there are steep slopes (gravitational potential energy) and where heavy rains and/or earthquakes occur to trigger the movement.
Aerial view of the La Conchita Landslide in California (Ventura County). This landslide formed on the hillslopes above the residential community built on a narrow coastal plain along the Pacific Ocean between Santa Barbara and Ventura. The landslide formed in soft (poorly consolidated) sediments on the western slope of Rincon Mountain. On January 10, 2005, an earthflow (landslide) at La Conchita destroyed or seriously damaged 36 homes and killed 10 people. Another landslide occurred in the same vicinity in 1995 (without catastrophic results) and the hillslopes in the area display abundant evidence of landslide activity in the prehistoric past. Note the bowl-shaped character of the upper escarpment area and the lobe-shaped geometry of the landslide deposits at the base (or toe) of the landslide. (Photograph by R.L. Schuster, U.S. Geological Survey, 1995.)
