Landslides occur when the slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone. Natural causes of landslides include:
groundwater (pore water) pressure acting to destabilize the slope
loss or absence of vertical vegetative structure, soil nutrients, and soil structure (e.g. after a wildfire - a fire in forests lasting for 3–4 days)
erosion of the toe of a slope by rivers or ocean waves
weakening of a slope through saturation by snow melt, glaciers melting, or heavy rains
earthquakes adding loads to barely stable slope
volcanic eruptions
Landslides by human activities, such as
deforestation, cultivation and construction, which destabilize the already fragile slopes.
vibrations from machinery or traffic
blasting
earthwork which alters the shape of a slope, or which imposes new loads on an existing slope
in shallow soils, the removal of deep-rooted vegetation
construction, agricultural or forestry activities which change the amount of water infiltrating the soil.