Viscoelastic mechanics of tidally induced lake drainage in the grounding zone

Abstract. Drainage of supraglacial lakes to the ice-sheet bed can occur when a hydrofracture propagates downward, driven by the weight of the water in the lake. For supraglacial lakes in the grounding zones of Antarctic glaciers, drainage mechanics are complicated by the glaciers' proximity to the grounding line. Recently, a series of supraglacial lake drainage events through hydrofractures were observed in the Amery Ice Shelf grounding zone, East Antarctica. The lake depth at drainage varied considerably between events, raising questions about the mechanisms that induce hydrofractures even at low lake depth. Here, we use a modelling approach to investigate the contribution of tidally driven flexure to hydrofracture propagation in the grounding zone. We model the viscoelastic response of a laterally unconfined marine ice sheet to tides, the tidally induced stress, and the contribution of this stress to hydrofracture propagation. A sensitivity analysis is used to explore the dependence of viscoelastic grounding-line dynamics on the material properties of ice and local bedrock bathymetry. We propose a model-based criterion that predicts hydrofracture and supraglacial lake drainage as a function of daily maximum tidal amplitude and pre-drainage lake depth in laterally unconfined grounding zones. Although lateral confinement may contribute to the dynamics of lake drainage at Amery, our model predictions are consistent with observations of hydrofracture events from this grounding zone.