All of the West Antarctic ice sheet draining into the Ross Ice Shelf lies on bedrock which is below sea level. This is thought to make it especially senstitive to rapid decay which could be triggered by an increase in atmospheric CO2 levels, ice stream B, one of the main outlets of the West Antarctic Ice Sheet, is thinning, possibly in response to changes in climate. However, Ice Stream C, its neighbor, is thickening.

One of the most effective ways to study ice streams is by repeat aerial photogrammetry. Thousands of velocity values and elevations are available for Ice Stream B using this technique. Two sections of the ice stream have repeat photogrammetry with control. Maps of elevations, velocity components and velocity gradients have been produced following the methods of Brecher (1986).

The area considered here is a 40 by 30 km block across a part of the ice stream. The maps show that most of the increase in longitudinal velocity occurs within about 6 km of the ice-stream margin and reaches a maximum of 460 m a-1 in the center of the stream. Strain rates in the shear margins reach 0.12 a-;1 and are an order of magnitude less in the main body of the stream.

The elevation maps show ridges and troughs. These features appear to be related to transverse velocities.