CLIMATIC CONDITIONS OF THE WESTERN UINTA ICE FIELD, UINTA MOUNTAINS, UTAH DURING THE LAST GLACIAL MAXIMUM INFERRED FROM GLACIER MODELING

The Western Uinta Ice Field (WUIF) occupied the western sector of the Uinta Mountains during the last Pleistocene glaciation, forming the largest single ice mass in the range. The time when the WUIF was at its maximum size is known in several glacial valleys from cosmogenic ¹⁰Be exposure dating of moraines, which indicate that outlets of the ice field occupied moraines near the time of the Lake Bonneville highstand at ca. 18 ka. The reconstructed, west-to-east rise in glacier equilibrium-line altitudes across this area suggests a strong climatic gradient downwind of Pleistocene Lake Bonneville, possibly reflecting local effects of the lake on glacier mass balance. A two-dimensional numerical model of glacier mass balance and ice flow applied to this area in previous studies is reevaluated here using higher resolution topographic and meteorological models. The known ice thickness and area in glacial valleys occupied by the WUIF was modeled at steady state using a broad range of temperature and precipitation combinations. Model results indicate that lesser temperature and/or precipitation changes relative to modern are needed for ice to fill the eastern valleys occupied by the WUIF, whereas greater temperature or precipitation changes are needed for ice to fill the western valleys. These results are consistent with previous modeling studies and the local trend in equilibrium-line altitudes, further supporting the idea that the magnitude of climate change during the last glaciation was greatest in valleys nearest Lake Bonneville.