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Physical processes controlling the rifting of Larsen C Ice Shelf, Antarctica, prior to the calving of iceberg A68 in 2017

Rignot, Eric1; Larour, Eric2; Scheuchl, Bernd1; Poinelli, Mattia3

Published Aug 30, 2021 on Dryad. https://doi.org/10.7280/D1TX1F

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Abstract

The sudden propagation of a major pre-existing rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica lead to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remainder of the ice shelf. As for other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated.  Here, we model the response of the ice shelf stress balance to ice shelf thinning and to thinning of the ice mélange encased in pre-existing rifts. We find that  ice shelf thinning does not re-activate the rifts; it heals them. In contrast, thinning of the mélange directly controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that a thinning of the ice mélange by 10-20 m is a sufficient condition to re-activate the rifts and trigger a large calving event, thereby establishing a direct link between climate forcing and ice shelf retreat that has not been used in ice sheet models. Rift activation may explain the early initiation of ice shelf retreat many years prior to hydro-fracture caused by the ponding of melt water at the ice shelf surface, hence for a smaller amount of climate warming.