The movement downslope of rock fragments and soil under the influence of gravity. The material concerned is not incorporated into water or ice, and moves of its own accord, but slides are often triggered by increase in water pressure on rocks and soil. Granular mass movements entail transport by large (> 0.06 mm) solid grains, mixed with less-dense intergranular liquid or gas, and include rock avalanches, debris flows, pyroclastic flows (Iverson and Vallance (2001) Geology 29, 2). See also Deplazes et al. (2007) Terra Nova 19, 4. A widely used classification of mass movement uses the combination of types of movement (falls, topples, slumps, slides, and flows) with the nature of the material (bedrock, debris, and fine soil); see R. Chorley et al. (1985). Many cases of mass movement include more than one type of movement.