Fractures and Floods: Small-scale spatial and temporal processes driving change in a relic ice-shelf basal channel

Genevieve Sauret , Erin C Pettit, Karen Alley, Ken Zhao, Meghan Sharp, Michelle Maclennan, Christian Wild, Martin Truffer

Basal channels, which form beneath ice shelves due to localized warm or fast-moving water, may weaken ice shelves by localizing deformation that promotes crevasse formation. Here, we test this hypothesis and investigate the role of fracturing and melt generation in the evolution of an ice shelf basal channel. We use ground-based ice-penetrating radar imaging of change over 3 years for the prominent "relic'' basal channel in the vulnerable Thwaites Eastern Ice Shelf. We find an interplay of unsteady melt dynamics, ice deformation, and fracturing in a channel that is responding to the loss of connection to its subglacial discharge source. The channel exhibits an asymmetric ‘M’ shape that we infer results from local melt plumes on sidewalls under weak along-channel currents. Compression in the ice and wind-driven snow redistribution may be responsible for an offset between the channel and its associated surface depression. From observed basal fracture features, we deduce that the stress regime promoted fracturing from approximately 2010 through 2015. These crevasses likely act as sources (floods) or sinks of meltwater, generating locally variable channel geometry. The channel stress regime, however, inhibits crevasses from crossing the channel. These processes, key to ice-shelf stability, are largely muted in satellite analyses.