Latest Pleistocene and Holocene glacier fluctuations in Mount Rainier National Park, Washington, USA

The timing of glacier fluctuations on Mount Rainier, in Washington State, USA, is examined using evidence from lateral moraines and lacustrine sediments. Radiocarbon ages of wood from paleosurfaces within lateral moraines of Nisqually, Emmons, Carbon and South Tahoma glaciers show that glaciers were depositing tills on lateral moraine flanks from ca. AD 130 and 530, and also after ca. AD 1300. Geochemical and petrographic analyses were conducted on tephra layer O (Mazama) and an unidentified tephra (layer GRY), retrieved from a Tipsoo Lake sediment core. A macrofossil from the core provides a minimum age of 8905 +/- 20 14C yr BP for layer GRY and underlying glacigenic sediments. Deglaciation of the cirque above Tipsoo Lake occurred ca. 10,900 - 10,600 14C yr BP, based on estimated lacustrine sedimentation rates. Results show that the timing of glacier fluctuations on Mount Rainier is consistent with chronologies from elsewhere in the Central North American Cordillera in the early and latest Holocene.