BASAL FRICTION OF ICE-STREAM-E, WEST ANTARCTICA

We use surface velocity derived from sequential Landsat imagery and a control method to estimate the basal-friction distribution of a major West Aatarctic ice stream. The area-averaged basal stress is approximately 1.4 x 10(4) Pa, or about 29% of the area-averaged driving stress of 4.9 x 10(4) Pa. Uncertainty of the derived area-averaged basal stress is difficult to assess and depends primarily on spatial variation of the flow-law rate factor in the constitutive law. Spatial variation associated with depth-averaged temperature variation gives an uncertainty of approximately +/-10(3) Pa. Approximately 60% of the ice stream has a basal-stress magnitude less than 10(4) Pa, and approximately 30% has less than 10(3) Pa. These characteristics suggest the presence of a mechanically weak, water-charged subglacial till. Small-scale sticky spots where basal friction exceeds the area-averaged driving stress are scattered irregularly across the subglacial regime and comprise approximately 15% of the ice-stream area. Sticky spots cluster in regions where Landsat imagery suggests structural features in the underlying bedrock.