This award is for support for a three year program to study stress transmission at three ice stream shear margins. The objectives are to determine how much of the motion of the ice streams is controlled from the inter-stream ridges, to compare the magnitude of this lateral drag with the driving stress on the ice stream, and with ice stream width and to determine whether lateral drag support is associated with lateral migration of the margin. The net force per unit ice-stream length transmitted between ridge ice and ice-stream ice will be deduced from measurements of strain rate. Field work will entail Twin Otter installation of remote camps that will each be occupied for about 12 days during the first season and about 6 days during the second. The Support Office for Aerogeophysical Research in Antarctica (SOAR) facility will conduct aerial surveys to determine ice thickness on the inter-stream ridges, as well as the ice thickness and surface slope on the ice streams. The field measurements will be complemented by repeat SPOT imagery of Ice Stream E adjacent to the field site, to allow velocities in the ice-stream side of the margin to be determined. Comparing these velocities to those obtained from the strain-grid surveys will provide an estimate of the amount of softening of the ice in the margins.
