Evidence for restricted ice extent during the last glacial maximum in the Koryak Mountains of Chukotka, far eastern Russia

Field evidence in the Koryak Mountains-Lake Mainitz region of far eastern R ussia supports three Pleistocene glacial advances. The early Wisconsinan an d pre-Wisconsinan glaciations are represented by broad lobate moraines exte nding as much as 30 km north of the Koryak Mountains. Field evidence demons trates that the terminal, lateral, and medial moraines, as well as meltwate r channels, dead ice topography, kettles, and other ash plains mark the ext ent of ice during the last glacial maximum (LGM), during which glaciers rea ched no more than 20 km beyond their present limits. Those emanating from t he southern Koryak Mountains may have reached the Bering Sea, Numerical and relative dating techniques support these results and test the theoretical models of the LGM in western Beringia, Erratics on moraines and glaciofluvi al terraces, common to all valleys at 13-13.8 m above river level, yield (C I)-C-36 exposure ages ranging from 10.08 to 25.78 ka, The Koryak Mountains- Lake Mainitz record of glaciation is spatially and temporally consistent wi th the glaciation pattern across central Beringia found in other terrestria l and marine records, Glacier growth in the Koryak Mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest Pacific region, Evidence from the northern Koryak Mountains ( lat 64 degrees"N, long 177 degrees E) indicates that the extent of ice in w estern Beringia was limited to mountain and valley glaciers during the LGM. This field-based research contradicts M.G. Grosswald's theoretical Beringi an ice sheet hypothesis.