Repeated Hydrofracture of a Supraglacial Lake above the Grounding Zone of Amery Ice Shelf, East Antarctica

Abstract:

Surface meltwater lakes can destabilize ice shelves through the process of hydrofracture, thereby reducing their buttressing effects and subsequently causing sea level to rise. Here, we present remotely sensed observations of repeated, rapid drainages of a ~4.3 km² supraglacial lake above the grounding zone of Amery ice shelf. We describe lake morphology evolution from 2013 to 2020 using a combination of Landsat 8, WorldView (~0.5 m resolution) optical imagery, and digital elevation models. Appearance of a 0.6 km linear crevasse along the drained lakebed in combination with several large uplifted ice blocks provide evidence of rapid lake drainage via vertical hydrofracture. We calculate lake volume variations over this time period using two methods: via classification of water presence and depth from Landsat 8 multispectral imagery, and by automated extraction of shoreline elevations and filling of a 2 m WorldView digital elevation model where the lake has drained. Optical imagery is supplemented with Sentinel-1 synthetic aperture radar observations to assess the ability of radar backscatter variations in capturing lake drainage events. Comparison of lake volumes with snowmelt simulated over the lake’s watershed by the regional climate model RACMO2.3p2 suggests interannual variability in meltwater production is reasonably captured in the model. Combined, these datasets suggest lake drainage and hydrofracture is not forced by a threshold lake volume, but potentially by tidally forced ice flexure near the grounding zone. Our observations, along with other lake drainage events observed and reported in similar settings, suggests accumulation of meltwater on ice shelves may be inhibited by drainage prior to flowing onto the ice shelf, thus representing a stabilizing mechanism despite enhanced meltwater production common to ice shelf grounding zones.