Mounds in Lake Tahoe, California-Nevada: A Model for Landslide Topography in the Subaqueous Environment

Abstract

Landslide movement of sediments is a significant mode of sediment transport in certain subaqueous environments. A detailed study of Lake Tahoe, California-Nevada has shown that a series of massive, basin-wide landslides deposited a large portion of the thick bottom sediments. The latest of these landslides was comparable in volume with the largest landslides ever recorded. Several large mounds occur on the floor of Lake Tahoe. It is postulated that these mounds were formed by landslides. At the base-of-slope environment, many mounds are well layered and rotated backward suggesting deposition as coherent slump blocks. Mounds further from the base of slope are circular or elliptical in area, have a pebbly mudstone sedimentary texture, display a disordered internal structure on seismic reflection profiles, and are located on an extensive layer of similarly disordered sediments. We suggest that such mounds formed along dewatering centers during the rapid deposition of an incoherent landslide mass. A subaqueous, landslide gradation exists between coherent slumps, partially fluidized, incoherent landslide masses, and fluidized turbidity currents depending on the amount of water that has been entrained. It is postulated that only the fluid flow does not form a characteristic mound topography.