QUIESCENT-PHASE EVOLUTION OF A SURGE-TYPE GLACIER - BLACK-RAPIDS GLACIER, ALASKA, USA

Black Rapids Glacier, a surge-type glacier in the Alaska Range, most r ecently surged in 1936-37 and is currently in its quiescent phase. Mas s balance, ice velocity and thickness change have been measured at thr ee to ten sites from 1972 to 1994. The annual speed has undergone cycl ical fluctuations of as much as 45% about the mean speed. Ice thicknes s and surface slope did nor change enough to cause the speed fluctuati ons through changes in ice deformation, which indicates that they are being driven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from th at of Variegated Glacier. another well-studied surge-type glacier in A laska. The present medial-moraine configuration of Black Rapids Glacie r indicates that a surge could occur al any time. However, ice velocit y data indicate that the next surge may not be imminent. We believe th at there is little chance that the next surge will cross and dam the D elta River.