MASS WASTING The downslope movement of surface material under the direct influence of gravity is called "Mass Wasting." Rapid Movements Slow Movements Gravity operates vertically but has a component acting parallel to the slope - this helps cause instability. Angle of Repose Rapid Mass Movements Rockfalls - Produced by rocks falling from near vertical cliffs, the rockfall is the smallest, most common, and most rapid from of mass wasting. Rapid transport of mixture of soil, rock, and vegetation down a moderate to steep slope signifies a debris slide, avalanche, or flow. A debris slide is the driest, while a debris flow is the wettest. Mudflows are the most fluid, rapid flow of mud, usually mixed with rocks and other debris, downhill. They generally occur following heavy rainstorms in arid regions, and follow preexisting channels, such as streams or valleys. Earthflows are slow flowage of nearly saturated soils down moderate to steep slopes. Earth flows are more fluid, shallower,and smaller than slumps. SLUMP - The intermittent movement (slip) of a mass of earth or rock along a curved plane is a slump. A slump is most likely to occur after a heavy rain, on a steep slope with deep, clay- rich soils. CREEP - The slowest and least noticeable, but most widespread of the slow mass wasting categories is creep. Creep involves the entire hillside, and is characterized by very slow movement of soil or rock material over a period of several years. Solifluction - downslope movement when ice melts in the upper portion of the soil SHEAR STRENGTH is a measure of the ability to withstand a change in shape. slope material's strength and cohesion amount of internal friction between grains any external support of the slope