Causes of Landslide

Geological causes
Weak materials
Sensitive materials
Weathered materials
Sheared materials
Jointed or fissured materials
Adversely orientated discontinuities
Permeability contrasts
Material contrasts
Rainfall and snow fall

Morphological causes
Slope angle
Uplift
Rebound
Fluvial erosion
Wave erosion
Glacial erosion
Erosion of lateral margins
Subterranean erosion
Slope loading
Vegetation change

Physical causes
Intense rainfall
Rapid snow melt
Prolonged precipitation
Rapid drawdown
Earthquake
Volcanic eruption
Thawing
Freeze-thaw
Shrink-swell
Ground water changes
Soil pore water pressure
Surface runoff
Seismic activity

Human causes
Excavation
Loading
Drawdown
Land use change
Water management
Mining
Quarrying
Vibration
Water leakage
Deforestation

http://en.wikipedia.org/wiki/Causes_of_landslides