BRUGGER, Keith A., Geology Discipline, University of Minnesota – Morris, Morris, MN  56267, bruggeka@mrs.umn.edu
MUNROE, Jeffrey S., Department of Geology and Geophysics, University of Wisconsin – Madison, Madison, WI  53706

Dated sequences of sediments exposed in moraines found in high cirque basins suggest that the Uinta Mountains remained ice free during the Holocene.  Equilibrium-line altitudes (ELAs) of the cirque glaciers responsible for deposition of these moraines are estimated to have been between ~3200 and 3500 m.  Two methodologies were used to determine the climate under which these glaciers could have existed.  The first compared modern temperatures and precipitation at paleo-ELAs with those found at ELAs of modern glaciers. The second method used degree-day modeling to determine those combinations of temperature and precipitation necessary to depress modern snowline to estimated paleo-ELAs.  Results of these analyses suggest that in the absence of significant changes in mean annual precipitation, mean summer temperatures required to maintain the glaciers would have been ~8 °C cooler than present.  Slightly wetter or drier conditions would have required, respectively, temperature depressions of about 7 and 9 °C.  Modest decreases in mean summer temperature (e.g. 3-4 °C) would have required concomitant increases in mean annual precipitation as much as 500 to 800% over modern values.  Such extremes in climate are inconsistent with the magnitude of regional variations in Holocene temperature and precipitation implied by other climate proxies, and thus support the contention that the Uinta Mountains were not glaciated during that interval of time.