MELTWATER CONTRIBUTION OF GLACIERS IN THE UINTA AND WASATCH MOUNTAINS TO PLUVIAL LAKE BONNEVILLE, UTAH, U.S.A

The watershed of Lake Bonneville, the largest of the Pleistocene paleolakes in the Great Basin, featured numerous glaciers in five mountain ranges in northern Utah. Recent updates to the Pleistocene glacial chronology of the Wasatch and western Uinta Mountains, which hosted the largest glaciers in the watershed, indicate that the timing of local glacier maxima closely coincided with the highstand of Lake Bonneville. However, the lake apparently maintained a positive hydrologic budget until after glaciers in these two ranges began retreating at 17 to 15 ka BP, despite widespread evidence of warming and drying of regional climate at this time. We estimate the contribution of melting glaciers in the Wasatch and western Uinta Mountains to the hydrologic budget of Lake Bonneville by simulating the known maximum ice extent in its drainage basin. Areal extents of mountain glaciers in the Wasatch and western Uinta Mountains that contributed meltwater to Lake Bonneville are determined from available mapping data and interpretations of 7.5-minute topographic maps, Google Earth images, and aerial photographs. Maximum ice extents in these areas are simulated by a two-dimensional mass/energy balance and ice flow model (of Plummer and Phillips, 2003). Results of modeling experiments indicate that the volume of ice in the Wasatch and Uinta Mountains is ca. 243 km³, less than three percent of the total volume of Lake Bonneville (ca. 9,500 km³). These findings indicate that the melting of glaciers in the Wasatch and western Uinta Mountains was a small component of the hydrologic budget of Lake Bonneville during the late Pleistocene and that the relatively late highstands of the lake were more likely sustained by a regional increase in effective precipitation. [Plummer, M.A., Phillips, F.M., 2003. A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. Quaternary Science Reviews 22, 1389–1406].