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002792 2.0 LANDSLIDE PROCESSES AND PREDICTION The term "landslide" is often used to describe a wide variety of processes that result in the downward and outward movement of slope-forming materials composed of rocks, soils, artificial fill, or a combination of these. The materials may move in any of the following ways: falling, toppling, sliding, spreading, or flowing (USGS, 1981). The various types of landslides can be differentiated by the kind of material involved and the method of movement. An example of a classi- fication system based on these parameters is shown in figure __' Other classifi- cation systems also incorporate such variables as the rate of movement and the water, air, or ice content. Different types of landslides are described below. TYPES OF LANDSLIDES Rockfalls and Other Earthfalls Falls are abrupt movements of rock masses which become detached from steep slopes or cliffs. Rock separation occurs along a surface on which little or no shear displacement takes place and movement occurs through free-fall. bouncing, and rolling (Varnes, 1978). Rockfalls (figure __) consist of detached masses of bedrock and are strongly influenced by the presence of fractures, joints, and bedding planes. Falls composed of other types of earth materials result in soil-falls, debris- falls, earth-falls, boulder-falls, and so on. All types of falls are promoted by undercutting, differential weathering, excavation, or stream erosion. Topples Toppling failures (figure ) are distinguished by "...the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the action of gravity and forces exerted by adjacent units or by fluids in cracks. It is tilting without collapse." (Varnes, 1978). Sl ides Althou9h many types of mass movement are included in the general term "1 ands 1 ide", the more restri ct ive use of the term refers to on ly "... those mass - 6 -