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ENGEO INCORPORATE D • Falls are abrupt free-falls of earth materials from cliffs, steep cuts, or steep stream banks, • Earthflows are mass movements of earth materials in which the type of movement is one of flowing. When composed of soil finer than gravel size, _ the flowing material is commonly called a mudflow. • Debris flow/debris avalanches are composed of natural earth materials, _ ~ artificial fill, and/or organic debris which flow downslope with speed. Most of the material is transported away from the area of initial ground failure. __ • Soil creep is the slow, often imperceptible, deformation of slope materials under low stress levels. It normally affects the shallow portion of the slopes, - but can be deep seated when a weak zone of soil or bedrock exists. It results from gravitational and seepage forces and may be indicative of conditions -- favorable for other types of landsliding. Creep can be caused by wetting and drying of clays, by solution and crystallization of salts, by the growth of roots, - by burrowing animals and by down-slope movement of saturated ground. • Colluvium refers to the mantle of loose soil and bedrock debris that progress J- down hillsides by creep. _ Landslides can consist of mass movements of earth materials which are primarily intact, and occur along discrete shear surfaces. These surfaces (shear or slip planes) can be rotational (conchoidal or concave), such as for earth slumps, or planar, as for translational earth slide or bedrock block glides. Most landslides are "complex landslides," sliding, falling and flowing with more than one type of movement and/or material. 6. Erosion: The process by which earth materials are loosened and removed by running water on the ground surface or in the subsurface. 4291-W2 July 17, 1997 _ Revised October 9, 1997 Revised October 22, 1997 8