Small-scale topographically-controlled glacier flow switching in an expanding proglacial lake at Breiðamerkurjökull, SE Iceland

Winsborrow and others (2012) reviewed the literature and proposed five mechanisms that may control flow switching: (1) accumulation of sediment causing accommodation space to be filled (Dowdeswell and others, 2006); (2) variations in bathymetry causing asynchronous response of ice flow (Stokes and others, 2009); (3) variations in basal thermal regime (Ó Cofaigh and others, 2010); (4) variations in subglacial meltwater routing and sticky spot location (Anandakrishnan and Alley, 1997); and (5) large-scale changes in mass balance (Payne and Dongelmans, 1997). Analysis of the terrestrial component of the 2015 DEM reveals that it is horizontally offset from the 1998 and 2007 DEMs by 7 m. It is systematically vertically offset by ~68 m, varying by a range of ~2 m either side of this value. [...]to measure surface changes, all DEMs were resampled to 50 m horizontal resolution, to conservatively remove any artefact of error in georeferencing. Rates of ice-surface lowering increased after 2007. Since 1985, Breiðamerkurjökull has undergone asynchronous retreat, with the fastest retreat occurring over the deepest parts of the Jökulsárlón trench (Fig. 1b; Supplementary animation), coincident with the loci of ice-surface lowering. [...]detailed knowledge of bed topography, and its influence on ice dynamics, is an essential source of information for predicting the fate of water-terminating ice in any setting.