SUBMARINE LANDSLIDES

Landslides are common on inclined areas of the seafloor, particularly in environments where weak geologic materials such as rapidly deposite d, fine-grained sediment or fractured rock are subjected to strong env ironmental stresses such as earthquakes, large storm waves, and high i nternal pore pressures. Submarine landslides can involve huge amounts of material and can move great distances: slide volumes as large as 20 ,000 km(3) and runout distances in excess of 140 km have been reported . They occur at locations where the downslope component of stress exce eds the resisting stress, causing movement along one or several concav e to planar rupture surfaces. Some recent slides that originated nears hore and retrogressed back across the shoreline were conspicuous by th eir direct impact on human life and activities. Most known slides, how ever, occurred far from land in prehistoric time and were discovered b y noting distinct to subtle characteristics, such as headwall scarps a nd displaced sediment or rock masses, on acoustic-reflection profiles and side-scan sonar images. Submarine landslides can be analyzed using the same mechanics principles as are used for occurrences on land. Ho wever, some loading mechanisms are unique, for example, storm waves, a nd some, such as earthquakes, can have greater impact. The potential f or limited-deformation landslides to transform into sediment flows tha t can travel exceedingly long distances is related to the density of t he slope-forming material and the amount of shear strength that is los t when the slope fails.