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 provide a record of late Quaternary climate change. Periglacial features include a large compound tongue-shaped rock glacier on the cirque floor, as well as several smaller lobate rock glaciers and protalus ramparts located around the perimeter of the cirque. Three closely spaced terminal moraines are located on the valley floor immediately downvalley from the terminus of the tongue-shaped rock glacier. The uppermost of the three moraines is partly overlapped by the lower lobe of the compound rock glacier, while the middle and lower moraines enclose small fens on their upstream sides.

Rock-weathering and lichenometric data collected at 11 stations on the periglacial deposits record three episodes of periglacial activity in post-Altithermal time. The lower lobe of the large tongue-shaped rock glacier, which is clearly pre-Altithermal in age, is likely to be of glacigenic origin and probably formed as ice downwasted during retreat from the upper moraine. Soils on the three moraines have an A/Bw/Cox profile similar to Satanta Peak soil profiles found in the adjacent Front Range. A radiocarbon date of 11,595 ¹⁴C yr BP obtained from basal sediment in a core taken from the fen behind the middle moraine provides a close minimum age for the moraine and suggests that deposition of the moraine may have been coeval with the European Younger Dryas event. A 23-cm-thick peat layer in the midsection of the same core yielded a radiocarbon date of 6200 ¹⁴C yr BP, and reflects a period of warmer climate and a rise of treeline before renewed cooling and periglacial activity.