Late Quaternary glaciation and equilibrium line altitude variations of the McKinley River region, central Alaska Range

Glacial deposits and landforms produced by the Muldrow and Peters glaciers in the McKinley River region of Alaska were examined using geomorphic and ¹⁰Be terrestrial cosmogenic nuclide (TCN) surface exposure dating (SED) methods to assess the timing and nature of late Quaternary glaciation and moraine stabilization. In addition to the oldest glacial deposits (McLeod Creek Drift), a group of four late Pleistocene moraines (MP-I, II, III and IV) and three late Holocene till deposits ('X', 'Y' and 'Z' drifts) are present in the region, representing at least eight glacial advances. The ¹⁰Be TCN ages for the MP-I moraine ranged from 2.5 kyr to 146 kyr, which highlights the problems of defining the ages of late Quaternary moraines using SED methods in central Alaska. The Muldrow 'X' drift has a ¹⁰Be TCN age of ∼0.54 kyr, which is ∼1.3 kyr younger than the independent minimum lichen age of ∼1.8 kyr. This age difference probably represents the minimum time between formation and early stabilization of the moraine. Contemporary and former equilibrium line altitudes (ELAs) were determined. The ELA depressions for the Muldrow glacial system were 560, 400, 350 and 190 m and for the Peters glacial system 560, 360, 150 and 10 m, based on MP-I through MP-IV moraines, respectively. The difference between ELA depressions for the Muldrow and Peters glaciers likely reflects differences in supraglacial debris-cover, glacier hypsometry and topographic controls on glacier mass balance.