CLIMATE CHANGES DURING THE LAST PLEISTOCENE GLACIATION AND DEGLACIATION INFERRED FROM NUMERICAL MODELING OF GLACIER MASS BALANCE AND ICE FLOW, EASTERN RUBY MOUNTAINS, NORTHEASTERN NEVADA

During the last Pleistocene glaciation, numerous valley glaciers occupied the Ruby Mountains. The Overland Creek valley featured the largest east-flowing valley glacier in the Ruby Mountains, which deposited a well-preserved sequence of terminal and recessional moraines. The timing of changes in ice margin position represented by these moraines is known from cosmogenic ¹⁰Be exposure ages of moraines and glacially polished bedrock. Ice retreated from a terminal moraine at ca. 22.1 ± 0.5 ka, deposited a recessional moraine at 17.1 ± 0.8 ka and retreated into Overland Lake near the head of the valley by 16.0 ± 0.5 ka. To improve the understanding of the temperature and precipitation changes during intervals of moraine deposition, 2-D numerical modeling of glacier mass balance and ice flow is used to simulate the known maximum and recessional ice extents. Results of model experiments indicate that if precipitation was close to modern, then a temperature depression of ~9.2°C accompanied deposition of the terminal moraine. This finding is nearly identical to results of model applications to west-flowing glacial valleys in the Ruby Mountains, where the timing of glacier maxima was synchronous with that in Overland Creek valley. Deposition of the recessional moraine occurred when the glacier was at 80% of its maximum length and coincided with the highstand of Pluvial Lake Franklin in the neighboring valley. If the lake highstand was driven by greater-than-modern precipitation, then the corresponding temperature depression at 17 ka was ca. 8°C or less. Steady ice retreat occurred after 17 ka despite persistence of Lake Franklin near its highstand until 15 ka, suggesting a transition to warmer and wetter climate during this time.