TIMING OF STAGNATION OF ICE STREAM-C, WEST ANTARCTICA, FROM SHORT-PULSE RADAR STUDIES OF BURIED SURFACE CREVASSES

Five short-pulse radar profiles were run across the edge of inactive I ce Stream C, one of the ''Ross'' ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from burie d crevasses, which we presume were at the surface of the ice stream wh en it was active, creates hyperbolae on the radar records. A density-d epth curve and local accumulation rates were used to convert the picke d travel times of the apices of the hyperbolae into stagnation ages fo r the ice stream. Stagnation ages are 130 +/- 25 year for the three pr ofiles farthest downstream and marginally less (100 +/- 30 year) for t he fourth. The profile farthest upstream shows a stagnation age of onl y approximately 30 year. We believe that these results indicate a ''wa ve'' of stagnation propagating at a diminishing speed upstream from th e mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.