CPP-05. Observed and modeled surface meltwater-induced flexure and fracture on north George VI Ice Shelf, Antarctica

Abstract
Global Navigation Satellite System (GNSS) observations and ground-based timelapse photography obtained over the record-high melt season of 2019/2020 are combined to characterize the flexure and fracture behavior of a mature (i.e., formed in years in the past) doline on north George VI Ice Shelf, Antarctica. The GNSS displacement timeseries shows a downward vertical displacement of the doline centre with respect to the doline rim of ~80 cm in response to loading from the development of a central meltwater lake. Viscous flexure modelling indicates that this vertical displacement likely generates flexure stresses of ~> 75 kPa. The GNSS data also shows a tens-of-days episode of rapid-onset, exponentially decaying horizontal displacement where the horizontal distance from the rim of the doline with respect to its center increases by ~70 cm. We interpret this event as the initiation and/or widening of a single fracture, possibly aided by the availability of surface meltwater. Our observations document for the first time the formation of a "ring fracture" on an ice shelf, equivalent to those fractures proposed to be part of the chain reaction lake drainage process involved in the breakup of Larsen B Ice Shelf in 2002.