LONGITUDINAL TRENDS OF LATE PLEISTOCENE EQUILIBRIUM-LINE ALTITUDES ACROSS THE COLORADO ROCKY MOUNTAINS: IMPLICATIONS FOR CLIMATE DURING THE LAST GLACIAL MAXIMUM

Recent mapping and analyses of topographic maps, aerial photographs, and digital elevation models allowed for the reconstruction of fifteen paleoglaciers in the West Elk Mountains at their last glacial maximum (LGM) extent. Equilibrium-line altitudes (ELAs) for the glaciers were determined using the accumulation-area method. These values, combined with previous ELA estimates similarly determined for paleoglaciers in the Elk Mountains and Sawatch Range (n = 40), document regional climate during the LGM. Along a transect spanning 120 km (corresponding to 2.5° of longitude) ELAs decrease eastwardly from about 3400 m to a low of 3050 m in the interior of the West Elks and then rise to as high as 3550 m in the Sawatch Range. Based on degree-day modeling, a regionally consistent LGM temperature decrease of about 7 °C is inferred from the ELAs and temperature depression appears to be the dominant driver of glaciation. ELA trends closely follow those in modern precipitation (expressed as residuals from the regional trend) in that they increase in drier, and decrease in wetter areas. Given the apparent strength of temperature forcing, this suggests that LGM precipitation, and more significantly that moisture transport, were not too dissimilar to today.