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How can heavy rainfall trigger a landslide?
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landslide
This 1995 landslide at La Conchita, a coastal town in California, swept away a hillside road and destroyed a number of houses.
Heavy rainfall triggers landslides by increasing shear stress and reducing the shear strength of slope materials.12
Rainfall contributes to slope failure through several mechanisms:
- Loading: The inflow of water adds significant weight to the slope, increasing the gravitational stress acting upon it.2
- Increased Pore Water Pressure: As water saturates the ground, it can increase pore water pressure, which reduces the internal friction that holds materials together.2
- Weakening Material: Water can weaken soil and rock by dissolving interparticle cements, hydrating clay minerals, and eliminating capillary tension that otherwise helps bind particles.2
- Short-term Stress: Intense rainstorms act as short-term triggers that can push a slope beyond its stability threshold, especially in areas with loose sediment fabric or steep gradients.12
When these factors cause the stress within a slope to exceed the material's resistance, the mass of rock, debris, or earth moves downslope.2