Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica

We present conventional and swath altimetry data from Cryosat-2 revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica. Much of the 10 drainage happened in less than six months, with an apparent connection between three lakes spanning more than 130 km. Hydropotential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed large-scale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events, suggesting that there are important limitations in the ability of hydropotential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests 15 that lake drainages of this type should take place every 20-80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier.