How do mountain rainstorms trigger landslides?

Landslides become more likely on steep mountain slopes when rainwater infiltrates soil and fractured rock. The added water increases pore pressure, which weakens the forces that hold material in place and makes slopes less stable. When the resisting strength is overcome, debris, soil, or rock can fail suddenly and rush downslope. Earthquakes, deforestation, and wildfires can make landslides more likely by loosening the ground or removing vegetation. In mountain regions, landslides are a major hazard during intense storms and monsoon seasons.