Glacial and periglacial deposits of the Lake of the Clouds cirque, Never Summer Mountains, Colorado

Glacial and periglacial deposits within the Lake of the Clouds cirque in the Never Summer Mountains of Colorado record four episodes of late Quaternary climate cooling. Three closely spaced end moraines are located on the valley floor approximately 1.7 km from the cirque headwall. The outer and middle moraines enclose small fens on their upstream sides, while the inner moraine is partly overlapped by a large compound tongue-shaped rock glacier. Several smaller lobate rock glaciers and protalus ramparts are located around the perimeter of the cirque.;Close parallelism of the moraines, as well as similarities in weathering and soil development, indicates that all three moraines are of similar age. A radiocarbon date of 11,595 +/- 35 14C yr BP obtained from basal sediment in a core taken from the fen behind the middle moraine indicates that the moraines are pre-Altithermal in age, but soil development and distance from the valley head point to a post-Pinedale age. The moraines are correlated tentatively with Satanta Peak moraines in the adjacent Front Range, and may have formed during a cold period coeval, at least in part, with the European Younger Dryas event. The lower lobe of the large tongue-shaped rock glacier is likely to be of glacigenic origin and probably formed as ice downwasted during retreat from the inner moraine as a consequence of climate warming.;Maximum warming occurred during the Altithermal. A 23-cm-thick peat layer in the midsection of the same sediment core yielded a radiocarbon date of 6200 +/- 25 14C yr BP, and reflects a period of warmer climate and a rise of treeline before renewed cooling and periglacial activity.;Rock-weathering and lichenometric data collected at eleven stations on the periglacial deposits record three episodes of renewed cooling and periglacial activity in post-Altithermal time. The first of these episodes, an early Neoglacial event, reactivated the upper part of the large, tongue-shaped rock glacier, and produced two lobate rock glaciers higher on the cirque wall. A second episode, correlative with Audubon activity, led to expanded snow cover unaccompanied by rock glacier activity. During a final episode of cooling, coeval with the Arapaho Peak advances in the Front Range, a smaller tongue-shaped rock glacier formed above Lake of the Clouds and remains active today.