LATE PLEISTOCENE EQUILIBRIUM–LINE ALTITUDES ON THE BLANCA MASSIF, SANGRE DE CRISTO RANGE, COLORADO

Field mapping and analyses of topographic maps, aerial photographs and digital elevation models were used to reconstruct the late-Pleistocene extent of glaciers in ten valleys that radiate from the high (>4200 m) peaks of the Blanca Massif. On the western flank of the massif, glaciers were constrained to flow in relatively straight, narrow valleys and were characterized by relatively thin ice (maximum ice thicknesses ~100 m). Typically these glaciers were sourced from a single cirque basin. In contrast, glaciers on the eastern and northern flanks were thicker (maximum ice thicknesses up to ~250 m) and wider, often fed by the accumulation in multiple cirques. The largest glacier, flowing northward from Blanca Peak via the Huerfano Valley, was ~12 km in length and covered an area of ~1.8 x 10⁷ m². Equilibrium-line altitudes (ELAs) for the reconstructed glaciers were determined using the accumulation-area ratio method (AAR = 0.65). ELAs vary between ~3440 to 3560 m, but tend to be lower by ~100 m on the northern, eastern, and possibly the southern sides of the massif. This trend of ELAs being lower on the eastern side is also apparent from the limited data available for the entire Sangre de Cristo Range in Colorado. Modern climate data are rather sparse, particular those needed to define vertical precipitation gradients and temperature lapse rates. Nevertheless, ELAs and ELA trends are used as the basis for inferring climate during the local last glacial maximum.