A landslide includes a wide range of ground movements, such as rock falls, deep failure of slopes and shallow debris flows.
The biggest reason for a landslide is that there is a slope and material goes down the slope because of gravity.
But other things also contribute to landslides:
- erosion by rivers, glaciers, or ocean waves makes slopes too steep
- rock and soil slopes made weak through saturation by snowmelt or heavy rains
- earthquakes that make weak slopes fail or crack the rocks that will eventually fall down
- volcanic eruptions produce loose ash deposits, heavy rain, and debris flows
- vibrations from machinery, traffic, blasting and even thunder may trigger failure of weak slopes
- weight from much rain or snow, stockpiling of rock or ore, from waste piles, or from buildings may stress weak slopes to failure and other structures
- groundwater pressure making the slope unstable
- in shallow soils, the removal of deep-rooted plants that bind the colluvium to bedrock
