NEW AND IMPROVED DETERMINATIONS OF VELOCITY OF ICE STREAM-B AND ICE STREAM-C, WEST ANTARCTICA

Measurements of velocity have been made on and next to Ice Streams B a nd C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velociti es are used to describe the confluence of flow into the ice streams an d the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier i nto the major ice streams. For those inter-stream ridges that have bee n studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is ach ieved through reduced drag at the glacier base and increased resistanc e associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to thos e at the head of Ice Stream B.