LATE PLEISTOCENE CLIMATE ON THE BLANCA MASSIF, SANGRE DE CRISTO RANGE, COLORADO

Late Pleistocene equilibrium-line altitudes (ELAs) were determined for seven reconstructed paleoglaciers on the Blanca Massif using the accumulation-area method. ELAs thus determined vary between 3415 and 3570 m, with a mean value of 3490 ± 55 m. ELAs on the eastern side of the massif are on average ~100 m lower than those on the western side, mirroring a trend observed over the entire length of the Colorado section of the Sangre de Cristo Range. This pattern suggests that southeasterly-derived moisture, which today disproportionately contributes to late winter-early spring precipitation on the eastern side of the range (especially significant at higher elevations), was similarly important for Late Pleistocene glacier mass balances. Degree-day modeling indicates that a temperature depression of ~7-8 °C is required to lower equilibrium lines to their Late Pleistocene altitudes on the Blanca Massif. The magnitude of this cooling is consistent with other estimates of late glacial climate change in the Southern and Central Rocky Mountain region. Modeling also implies that while precipitation enhancement on the eastern side of the massif due to southeasterly-derived moisture is apparently required to explain differences in paleo-ELAs, it need not have been substantially strengthened during the Late Pleistocene.