LATE PLEISTOCENE ALPINE GLACIAL OSCILLATIONS IN THE NORTH CASCADES, WA AND SAWTOOTH MTS., ID AND THEIR RELATIONSHIP TO GLOBAL CLIMATIC CHANGES

Late Pleistocene glacial oscillations in the Sawtooth Mts. of Idaho built multiple cirque moraines during and shortly following the LGM. The LGM at Redfish Lake is represented by a 16-moraine sequence near its maximum extent. Three successive episodes of moraine building occurred in cirques at altitudes of 7700-8400’ (2300-2550 m) in the upper Redfish Lake drainage.

Similar relations are seen in the North Cascades of Washington where construction of LGM moraines was followed by building of moraines well upvalley from the terminal zone in Icicle Creek, in cirques near Mt. Rainier, at Snoqualmie Pass, and on Mt. Baker. In the Icicle Creek drainage, multiple moraines in at least two tributary valleys suggest Younger Dryas (YD)¯Inter-Allerod Cold Period (IACP) events. Well upvalley from these moraines, younger moraines may represent early Holocene or very latest Pleistocene climatic changes. Cirque moraines near Mt. Rainier yield dates correlative with Younger Dryas and IACP climatic events. At Snoqualmie Pass, peat between post-LGM moraines suggests both YD and IACP glacial responses to climatic changes.

Two, well-dated, YD moraines were built by the Cordilleran Ice Sheet in the northern Puget Lowland 10,980-10,250 14C yrs B.P. and ~10,250-10,000 14C yrs B.P. Post LGM conditions in the North Cascade Range are more complicated. Disappearance of the Cordilleran Ice Sheet in the Cascades was followed by pre-YD, long, alpine valley glaciers, then smaller YD and early Holocene glaciers in the upper drainages.