Morphology and processes in Lake Tahoe (California-Nevada)

Lake Tahoe was surveyed using a state-of-the-art, high-resolution, multibea m mapping system to provide an accurate base map for the myriad of ongoing environmental studies in and around the lake. The newly defined basin morph ology shows steep basin margins on the northern, eastern, and western sides and a gentle margin on the southern side. Two large, flat plateaus several kilometers wide extend from the shore to about 40 m water depth in the nor thern and northwestern sections of the basin. A series of ridges in the wes t and north are presumed traces of faults, some of which border the lake ba sin and some of which traverse across the northern section of the lake and converge in McKinney Bay, McKinney Bay is a large reentrant in the western margin that was created by. a failure of the western margin that occurred a bout 300 ka, The failure generated a major debris avalanche that carried la rge blocks, some more than 1000 In long and 80 m high, across the basin. Ap parently, the debris avalanche was deflected by the eastern margin of the b asin and flowed to the north and south. Small debris flows and slides have continued to occur in this area. Small debris aprons occur along the northe rn, western, and eastern margins, some apparently the remnants of collapsed terminal moraines formed in the basin from the 160 ka Tahoe Glaciation, wh ich reached the edge of the basin. Eroded plateaus and ridges occur on a gl acial outwash plain that covers the gentle southern margin. The plateaus an d ridges are inferred to be remnants of another large terminal moraine of t he Tahoe Glaciation.