Airborne radar soundings of the ice sheet surface made in 1984-1985, together with elevations measured by oversnow transverse between 1957 and 1964 have been used to produce a surface elevation map of ice streams A, B, and C and much of the region around them. The flight positions and elevations were tied to many ground control stations whose positions in three dimensions were fixed by satellite tracking. Ice thicknesses were also measured along the flight lines but have not yet been mapped. The surfaces of active ice streams A and B exhibit a longitudinal ridgethrough topography of uncertain origin. Prominent surface valleys are associated with most, but not all, of their marginal shear zones. There is a deep glacial through beneath the grid north-eastern side of ice stream A that connects to the subglacial through beneath Reedy Glacier. The boundary between ice streams B1 and B2, to two tributaries of ice stream B, persists as a suture zone for 250 km downstream from their merger. Ice stream B1 overlies a relatively deep subglacial trough that continued under the corresponding part of ice stream B until it disappears close to the grounding line. Between ice streams B1 and B2 there is a complex zone containing several regions of undisturbed ice separated by bands of disturbed ice, which suggest to us that ''rafts'' of ice are being incorporated into the ice streams.

The previosly reported negative mass balance for the drainage system of ice stream B may arise from the expansion of the ice stream into the interior of the West Antarctic ice sheet. Crevasse bands at some places on ridge AB, together with high glacial velocities reported elsewhere, also suggest this expansion. Close to the Ross Ice Shelf, ice stream B widens into a nearly flat area where the mean surface slope is only 3.5¿10-4, and the surface elevations are only a few tens of meters above hydrostatic equilibrium. Inactive ice stream C differs from active ice streams A and B in surficial and basal characteristics. No elongated ridges and troughs are observed; instead, the ice stream surface exhibits several terraces, including some maxima and minima in elevation. Radar sounding reveals areas where basal echoes are strong and steady, indicating subglacial water, alternating with areas of weaker echoes with short fading lengths. Calculations indicate that the strong reflections require a water layer at least several centimeters to several meters thick, depending on the electrical conductivity of the water. Due to reversals in the surface slope, the hydrologic potential gradient changes sign several times along ice stream C, which implies that subglacial water should collect in some locations. ¿ American Geophysical Union 1987