Landslide Hazards

Landslides include a wide range of phenomena involving downslope ground movement, such as rockfalls, deep slope failure, shallow debris flows, and avalanches. Gravity acting on a slope is the primary cause of landslides, but there are other important and dynamic factors that serve as triggers.

• Saturation of slopes by precipitation (rain or snowmelt) weakens soil and rock by reducing cohesion and increasing the pressure in pore spaces, pushing grains away from each other.
• Erosion and undercutting of slopes by streams, rivers, glaciers, or waves increase slope angles and decrease slope stability.
• Earthquakes create stresses that weaken slopes and physically cause slope movement.
• Perhaps most significant from a management perspective, the over weighting, and/or under cutting of slopes for facilities, roads, trails, mines, and other man-made structures change the natural slope equilibrium and cause slopes to fail.

Types of slope movement. Different categories of slope movement are defined by material type, nature of the movement, rate of movement, and moisture content.

Trista L. Thornberry-Ehrlich, Colorado State University modified from Varnes, D. J. 1978. Landslides: analysis and control.