Timing and extent of Late Pleistocene glaciation in the Chugach Mountains, Alaska

Geomorphic mapping, landform and sediment analysis, and cosmogenic Be-10 and Cl-36 ages from erratics, moraine boulders, and glacially polished bedrock help define the timing of the Wisconsinan glaciations in the Chugach Mountains of south-central Alaska. The maximum extent of glaciation in the Chugach Mountains during the last glacial period (marine isotope stages [MIS] 5d through 2) occurred at similar to 50 ka during MIS 3. In the Williwaw Lakes valley and Thompson Pass areas of the Chugach Mountains, moraines date to similar to 26.7 +/- 2.4, 25.4 +/- 2.4, 18.8 +/- 1.6, 19.3 +/- 1.7, and 17.3 +/- 1.5 ka, representing times of glacial retreat. These data suggest that glaciers retreated later in the Chugach Mountain than in other regions of Alaska. Reconstructed equilibrium-line altitude depressions range from 400 to 430 m for late Wisconsinan glacial advances in the Chugach Mountains, representing a possible temperature depression of 2.1-2.3 degrees C. These reconstructed temperature depressions suggest that climate was warmer in this part of Alaska than in many other regions throughout Alaska and elsewhere in the world during the global last glacial maximum.