Supraglacial Lake Drainage Initiated by Tidally Induced Hydro-fracture on Amery Ice Shelf

Supraglacial lake drainage on marine ice sheets serves as an important link between surface melt and ice-shelf stability. Trusel et al. [2022] observe repeated supraglacial-lake drainage events at the Amery Ice Shelf grounding zone during the period 2014-2020. Evidence indicates that these drainage events occurred by hydro-fracture, typically triggered when the lake attains a critical volume of water [van der Veen, 2007]. However, the events coincide with periods of high tidal amplitude and variable lake volumes, leading Trusel et al. [2022] to hypothesise that hydro-fracture initiation is promoted by the stresses associated with tidal flexure.

Here, we quantify this hypothesis and test its relevance for the observations. Using the variational formulation of viscous grounding-zone dynamics in Stubblefield et al. [2021], we develop a model of viscoelastic tidal flexure. This is used to estimate the flexural-stress contribution to supraglacial drainage via hydro-fracture occurring in the grounding zone. Results show that downward tidal flexure can lead to significant tensile stress near the ice surface in a migrating grounding zone. Based on the model results, we derive a quantitative criterion for supraglacial-lake drainage events in the grounding zone and apply it to the observations on Amery Ice Shelf.

ReferencesAaron G Stubblefield, Marc Spiegelman, and Timothy T Creyts. Variational formulation of marine ice-sheet and subglacial-lake grounding-line dynamics. Journal of Fluid Mechanics, 919, 2021.Luke D Trusel, Zhuolai Pan, and Mahsa Moussavi. Repeated tidally induced hydrofracture of a supraglacial lake at the amery ice shelf grounding zone. Geophysical Research Letters, 49(7):e2021GL095661, 2022.C. J. van der Veen. Fracture propagation as means of rapidly transferring surface meltwater to the base of glaciers. Geophysical Research Letters, 34(1), 2007.