Observation and analysis of ice flow in the largest Greenland ice stream

We have applied satellite radar interferometry methods to map the velocity field of the recently discovered Northeast Greenland Ice Stream. We have used these data in conjunction with ice thickness and accumulation data to determine that the ice stream is in balance within the measurement errors. We used control methods to invert a finite element model of ice sheet flow constrained by the data to infer the ice stream's basal shear stress distribution. Our results reveal that flow in a section of the downstream end has much in common with the streaming flow of the Ross Ice Streams of West Antarctica (e.g., a weak bed and fast flow in the presence of low driving stresses). For several hundred kilometers along the middle of the ice stream, the basal shear stress balances the driving stress. In the upstream area, where the ice stream is first visible in the velocity data, the bed appears to be weak, which may contribute to the initiation of the ice stream.