NSFGEO-NERC: Ice-shelf Instability Caused by Active Surface Meltwater Production, Movement, Ponding and Hydrofracture

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The floating ice shelves around Antarctica provide a buffer against rapid ice flow from the continent's interior to the ocean. If that buffer is reduced or removed, there will be more rapid ice flow to the ocean contributing to sea level rise. Understanding the controls on ice shelf stability, therefore, is important for the assessment and prediction of possible ice shelf shrinkage or collapse. Evidence shows that one source of ice shelf instability comes from surface melting and the movement of the meltwater. The decade-long development of >2500 surface lakes on the Larsen B Ice Shelf, followed by their abrupt drainage, were the two most conspicuous precursors to the ice shelf's sudden collapse in 2002. This project will investigate how ice shelves fracture when subjected to strong surface melting using a suite of geophysical observations on the George VI Ice Shelf (GVIIS) of the Antarctic Peninsula. The leading processes to be observed are viscoelastic ice-shelf flexure and fracture in response to surface meltwater movement, loading, and unloading. The team's prior fieldwork provided the first direct measurements of these processes on the McMurdo Ice Shelf (McMIS). However, the results were somewhat limited in their application to other ice shelves due to a heterogeneous debris cover and therefore atypical ablation rates, sparsely-distributed ponds, and ice-flexure measurements made close to an active rift.Compared to the McMIS, the GVIIS provides a near-perfect opportunity to observe meltwater loading processes, as satellite imagery shows it hosts hundreds of lakes and displays features of viscoelastic rebound in response to lake drainage. Furthermore, GVIIS is thought not to be at risk of imminent breakup due to its compressive stress regime, making the ice shelf a safe working environment. The proposed 4-year project will conduct a 27-month period (November 2019 - January 2022) of measurements on the GVIIS. Seismometers, global positioning system (GPS), water pressure transducers, two automatic weather stations, and thermistor strings will be deployed to record fracture seismicity, ice shelf flexure, water depths, and surface and subsurface melting, respectively, in and around identified meltwater features. These instruments will be deployed in a 20 x 20 km field area immediately adjacent to BAS's Fossil Bluff Station. Field data will be used to validate and extend the team's existing approach to modelling ice-shelf flexure and stress that can lead to hydrofracture, drainage of surface water to the ocean below, and possible Larsen-B style ice-shelf instability.