Mass Wasting in Southern California
More mass movement occurs in southern California than in any other region of the United States. Multiple factors contribute to this slope instability. Some of these include the area's steep hillsides, weak bedrock materials, adverse geologic structures, and heavy episodic precipitation. Recent landslides in Pacific Palisades, Palos Verdes, San Clemente, and Anaheim Hills have caused millions of dollars in damage. Moreover, as development continues to expand, southern California's landslide problem is only expected to worsen.
Mass earth movements are highly variable. Typically, they occur within the following spectrum: e.g., from movements which are dependent upon some fluid, to those which are not. In subaerial environments, this spectrum comprises falls, slides, and flows (Blatt et al. 176). Rockfalls consist of detached masses moving down steep slopes. With such movements there is little or no shear displacement between the two original materials. Rockfalls typically result in piles of scree (Campbell et al. 1-27).
In contrast, landslides occur when a sediment mass overcomes its own cohesion and internal friction. Once detached, slides remain in constant contact with the underlying slope materials. Relative movement within the mass may take place on "discrete shear planes (Blatt et al. 176)." These planes divide the mass into subunits. In fact, the main resistance to slide mass movements consists of frictional forces acting at these shear planes. Among slides that move slowly over smooth basal slip surfaces, there may be relatively minor internal flow deformation. However, other slides can involve considerable flow disruption. Landslides may be subdivided into both slides and slumps. The two terms tend to be synonymous, both involve the movement of extremely variable block sizes ranging from large boulders to fine grains. Translational slides, however, commonly inv...