The triggering of sub-glacial lake drainage during the rapid glacier drawdown: Crane Glacier, Antarctic Peninsula

Ice surface altimetry from ICESat-1 and NASA aircraft altimeter overflights spanning 2002– 09 indicate that a region of lower Crane Glacier, Antarctic Peninsula, shows an unusual temporal pattern of elevation loss: a period of very rapid drawdown ( 91ma between September 2004 and September 2005) bounded by periods of large but more moderate rates (23ma until September 2004; 12ma after September 2005). The region of increased drawdown is 4.5 km 2.2 km based on satellite (ASTER and SPOT-5) stereo-image digital elevation model (DEM) differencing spanning the event. In a later differential DEM the anomalous drawdown feature is not seen. Bathymetry in Crane Glacier fjord reveals a series of flat-lying, formerly subglacial deeps interpreted as lake sediment basins. We conclude that the elevation-change feature resulted from drainage of a small, deep subglacial lake. We infer that the drainage event was induced by hydraulic forcing of subglacial water past a downstream obstruction. However, only a fraction of Crane Glacier’s increase in flow speed that occurred near the time of lake drainage (derived from image feature tracking) appears to be directly attributable to the event; instead, retreat of the ice front off a subglacial ridge 6 km downstream of the lake is likely the dominant cause of renewed fast flow and more negative mass balance in the