COMPOSITE PLEISTOCENE SNOW LINE OF OLYMPIC MOUNTAINS AND CASCADE RANGE, WASHINGTON

A composite Pleistocene snow line for the Olympic and Cascade ranges, based on altitudes of lowest north-facing cirques, increases in altitude inland (east or northeast) in both ranges. In the Cascade Range of southern Washington the rate of inland rise of Pleistocene cirque floors approximately equals that of small alpine glaciers. This relationship suggests that lower temperature may have been the primary factor controlling depression of the snow line during glaciations in this region. In the northern Cascade Range and in the Olympic Mountains, however, the eastward rise of Pleistocene cirque floors is steeper than that of small modern glaciers suggesting that significant reduction in precipitation at glacial maxima in those two areas offset the effects of decreased temperature, and the snow line was depressed differentially. Very likely this reduction in precipitation resulted largely from strong local climatic influences exerted by the Puget Lobe of the Cordilleran Glacier Complex that extended into the lowland between the Olympic Mountains and Cascade Range during successive glaciations.