LAST GLACIAL MAXIMUM EQUILIBRIUM-LINE ALTITUDES AND PALEOCLIMATE, NORTHEASTERN UTAH

SHAKUN, Jeremy D., Geology, Middlebury College, Bicentennial Hall, Middlebury, VT 05753, jshakun@middlebury.edu, MUNROE, Jeffrey S., Geology Department, Middlebury College, Bicentennial Hall, Middlebury, VT 05753, and LAABS, Benjamin J.C., Geology and Geophysics, Univ of Wisconsin, 1215 W. Dayton St, Madison, WI 53706

Thirty Last Glacial Maximum (LGM) valley glaciers from the Uinta and Wasatch Mountains of northeastern Utah were reconstructed. Their equilibrium-line altitudes (ELAs) were determined using four methods: accumulation-area ratio (of 0.65), toe-headwall altitude ratio (of 0.4), highest extent of lateral moraines, and the lowest cirque-floor elevation methods. The ELA estimates from each of these four methods were combined in a weighted average to yield an LGM ELA for each of these glaciers. LGM ELAs rose steadily eastward from 2460 m on the Wasatch Front to 3120 m at the eastern end of the Uintas. This significant westward ELA depression may have been due to pluvial Lake Bonneville-enhanced snow precipitating over the Wasatch Range and western Uintas, leaving areas further downwind (i.e., east) of Lake Bonneville progressively snow-starved. The ELA gradient also indicates that, in winter months, atmospheric circulation in northeastern Utah during the LGM was dominantly west to east.

LGM ELAs were also determined for five valley glaciers from the Stansbury Range of north-central Utah, and the East Humboldt Range and Ruby Mountains of northeastern Nevada, these latter two ranges having been just west of Lake Bonneville. ELAs in these ranges (2540 m to 2730 m) were somewhat higher than those in the Wasatch and western Uintas despite their relative proximity to the major moisture source of the Pacific Ocean; this may also reflect the influence of Lake Bonneville on ELAs in northeastern Utah.

LGM ELAs on the south slope of the Uintas were ~50 m lower than those on the north slope of the range, even though more ablation likely occurred on the south slope due to its aspect. This implies the south slope received significantly more winter precipitation than the north slope, which may have come in the form of Bonneville lake-effect snow derived from southwest of the Uintas.