Mass Movements and Hazard Risk

Mass movement is the downslope movement of rock, soil, and debris under the influence of gravity. Although gravity is the driving force, mass movements are frequently triggered by geophysical events, which is why they belong in this unit. Earthquakes shake unstable slopes loose, volcanic eruptions produce lahars and debris avalanches, and heavy rainfall saturates the ground until it fails. Understanding these processes and how they interact with human settlement is central to assessing hazard risk.

Mass movements vary in speed and material. Rockfalls are the sudden free fall of rock fragments from steep cliffs. Landslides, or slides, involve the movement of a coherent block of material along a distinct slip surface, often lubricated by water. Slumps rotate along a curved surface, tilting t