We analyze data acquired by the CryoSat-2 interferometric radar altimeter and demonstrate its novel capability to track topographic features on the Antarctic Ice Sheet. We map the perimeter and depth of a 260km surface depression above an Antarctic subglacial lake (SGL) and, in combination with Ice, Cloud and land Elevation Satellite laser altimetry, chart decadal changes in SGL volume. During 2007-2008, between 4.9 and 6.4km of water drained from the SGL, and peak discharge exceeded 160ms. The flood was twice as large as any previously recorded and equivalent to~10% of the meltwater generated annually beneath the ice sheet. The ice surface has since uplifted at a rate of 5.6±2.8myr. Our study demonstrates the ability of CryoSat-2 to provide detailed maps of ice sheet topography, its potential to accurately measure SGL drainage events, and the contribution it can make to understanding water flow beneath Antarctica. Key Points: Assessment of novel CryoSat-2 interferometric altimetry over land ice Demonstration of interferometric capability to track off-nadir topography Mapping of largest Antarctic subglacial lake drainage event observed to date
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