EXTENT AND CLIMATIC IMPLICATIONS OF THE UPPER TRUCKEE GLACIER DURING THE TAHOE GLACIATION – ASSESSING CONFLICTING SCENARIOS

Late Pleistocene moraines in the Upper Truckee basin, central Sierra Nevada, California, are small and have proved difficult to map, particularly those related to the penultimate Tahoe Glaciation. Several conflicting concepts exist for the extent of the Tahoe glacier; 1) a glacier that reached into the south shore of Lake Tahoe, 2) a glacier that reached to within 5 km of the south shore, and 3) a glacier with a terminus 10-12km upvalley from the modern south shore of Lake Tahoe. Determining the extent of the glacier during the Tahoe Glaciation is critical for not only resolving these conflicting concepts, but also to assess the climatic conditions associated with the late Pleistocene glaciations in the central Sierra Nevada. We test the various models through a combination of detailed field mapping, equilibrium-line altitude (ELA) reconstructions, and glaciologic flow modeling. We reconstructed a glacier for each of the three models proposed using mapped ice limits. From these reconstructions, we estimated ELA’s for each using an accumulation area ratio of 0.65. The least extensive model for the Tahoe glacier suggests an ELA of ~2500 m. The most extensive model indicates an ELA of ~2070 m, and the intermediate model has an ELA of ~2250 m. Comparison to other, better defined Tahoe deposits in the area suggests that the ELA’s of the two more extensive reconstructions are too low for Tahoe, and thus may relate instead to moraines of an earlier advance, or to another origin (e.g. dropstones, outwash, etc.). Initial constraints from glaciologic flow-modeling also support this conclusion. Comparison of modern climate conditions at the paleo-ELA’s may help us further constrain climate change associated with these deposits.