3-DIMENSIONAL DEFORMATION MEASURED IN AN ALASKAN GLACIER

Measurements of movement along 28 boreholes reveal the three-dimension al flow field in a 6 million cubic meter reach of Worthington Glacier, a temperate valley glacier Located in Alaska. Sliding at the bed acco unted for 60 to 70 percent of the glacier's surface motion. Strain rat es in the ice were low from the surface to a depth of about 120 meters , but then increased rapidly toward the bed. Ice deformation was not a ffected by temporal changes in the sliding rate. The three-dimensional pattern of motion indicates that plane strain, which is often assumed by models, is a poor approximation of this viscous flow.