CLIMATE CHANGE DURING DEGLACIATION OF THE ANGEL LAKE VALLEY, EAST HUMBOLDT MOUNTAINS, NEVADA, U.S.A

The type local for the last Pleistocene glaciation in the Great Basin, the Angel Lake valley, affords an opportunity to reconstruct the pattern of ice retreat during deglaciation. Here, ages of a well preserved suite of moraines and an up valley bedrock surface are known from cosmogenic ¹⁰Be exposure dating, indicating that retreat from the terminal moraine commenced at 19.4 ± 0.7 ka, and then ice paused or readvanced to deposit moraines in recessional positions at 18.9 ± 1.0, 18.1 ± 0.5 and 16.6 ± 0.9 ka. The ice margin retreated to a position above Angel Lake by 14.2 ± 0.8 ka. We apply a two-dimensional numerical model of mass balance and ice flow to the valley to identify temperature and precipitation combinations accompanying three distinct recessional positions indicated by dated moraines. Results of modeling experiments indicate that temperature rose by a minimum of ~2°C while ice retreated from the terminal to the innermost moraine in the valley. The magnitude of warming was likely greater due an increase in effective precipitation that likely accompanied the expansion of nearby Pleistocene Lake Clover at 17 ka. Additional warming of 2°C or greater accompanied retreat of the ice margin from the innermost moraine that dams Angel Lake. This pattern agrees with deglacial chronologies and inferred warming from elsewhere in the Great Basin and from the Middle and Southern Rocky Mountains.