Defining basal geometry and force balance at Columbia Glacier, Alaska

Basal geometry and internal stress patterns are unknown in the Eastern Trunk region of the Columbia Glacier, Alaska. Direct physical measurements are difficult due to the highly broken and hazardous glacial surface. A continuity model is used to estimate basal topography over this region using surface velocity data derived from aerial photographs taken in 2004. A breakdown in the continuity model, related to anomalous extensional strain rates near the terminus, is observed and inspected. A correction is made to improve the continuity results. A statistical method is implemented to characterize the marginal topography where continuity produces poor results due to high shear rates. Force balance analysis is used to define the internal stress patterns as they existed in 2004. Driving stresses are balanced with resistive stresses derived from the observed surface strain rates. These forces are useful in inferring the future behavior of the retreat.