Quaternary History of Lake Tahoe, California-Nevada
Lake Tahoe, California-Nevada, occupies a graben near the crest of the Sierra Nevada. The lake basin was formed by faulting and volcanism about 2 m.y. ago and contains more than 400 m of sediments. Alternating layers of well-layered sediments and sediments displaying chaotic internal reflections characterize the seismic reflection stratigraphy of the central lake basin. During Pleistocene glaciations, valley glaciers dammed Truckee Canyon, the lake9s outlet, raising the lake level. Joklhlaups (floods through breached ice dams) rapidly lowered the elevated lake level to the present lake level. It is postulated that glacial outwash deltas prograded out along the western, northern, and southern shores of the lake at elevated lake levels and slumped into the lake basin during the periods of rapid lake level lowering. Evidence for the slumping is seen in the irregular topography at the base of the western sidewall and chaotically reflecting sediment layers extending into the central lake basin. The slump layers are covered and underlain by Holocene and interglacial well-layered sediments of turbidite and suspensate rain origin. Three possible periods of glacial progradations followed by massive slumping are proposed and are correlated with the Hobart, Donner Lake, and Tahoe glaciations of the drainage basin. The more recent Tioga glaciation was less extensive than the other glaciations and resulted in limited slumping.