LANDSLIDE

also called Landslip, downward mass movement of earth or rock on unstable slopes, including a number of forms that result from differences in rock structure, coherence of material involved, degree of slope, amount of included water, extent of natural or artificial undercutting at the base of the slope, relative rate of movement, and relative quantity of material involved. Many terms cover these variations; creep, earthflow, mudflow, solifluction, and debris avalanche are related forms in which mass movement is achieved by flowage. If shearing movement occurs on a surface on consolidated rock, the dislocated mass is a debris slide. Cliffs may become so steepened through undercutting by rivers, glaciers, or waves that masses of rock will fall freely and constitute a rockfall type of landslide.