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. 2021 May 11;12(1):2701.
doi: 10.1038/s41467-021-23070-7.

Marine ice-cliff instability modeling shows mixed-mode ice-cliff failure and yields calving rate parameterization

Anna J Crawford  1 , Douglas I Benn  2 , Joe Todd  3 , Jan A Åström  4 , Jeremy N Bassis  5 , Thomas Zwinger  4
Affiliations

Marine ice-cliff instability modeling shows mixed-mode ice-cliff failure and yields calving rate parameterization

Anna J Crawford et al. Nat Commun. .

Abstract

Marine ice-cliff instability could accelerate ice loss from Antarctica, and according to some model predictions could potentially contribute >1 m of global mean sea level rise by 2100 at current emission rates. Regions with over-deepening basins >1 km in depth (e.g., the West Antarctic Ice Sheet) are particularly susceptible to this instability, as retreat could expose increasingly tall cliffs that could exceed ice stability thresholds. Here, we use a suite of high-fidelity glacier models to improve understanding of the modes through which ice cliffs can structurally fail and derive a conservative ice-cliff failure retreat rate parameterization for ice-sheet models. Our results highlight the respective roles of viscous deformation, shear-band formation, and brittle-tensile failure within marine ice-cliff instability. Calving rates increase non-linearly with cliff height, but runaway ice-cliff retreat can be inhibited by viscous flow and back force from iceberg mélange.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Mode of structural failure in which tensile failure follows viscous deformation.
a Viscous deformation of a glacier geometry as modeled in Elmer/Ice. The Cauchy shear stress tensor component aligned with flow direction (σyz) shows a maximum at the base and waterline of the calving face. b The geometry and σyz field shown in (a) prior to viscous deformation. c The brittle-elastic version of the Helsinki Discrete Element Model (HiDEMbe) domain initialized with the output geometry of the Elmer/Ice simulation in a. d An example of brittle failure in HiDEMbe caused by tensile stress at the glacier surface leading to surface crevassing and calving via forward block rotation. H = calving face thickness; Hc = ice-cliff height.
Fig. 2
Fig. 2. Retreat rates resulting from ice-cliff failure as a function of glacier thickness or cliff height.
Points represent results from the Elmer/Ice–HiDEMbe (the brittle-elastic version of the Helsinki Discrete Element Model) simulation series, which considers the interaction of viscous deformation and brittle failure. Scenarios with varying ice temperatures (Tice) and bed conditions (Bn, Bf and Bh representing normal, approaching frozen and high-slip conditions, respectively) are colour coded as follows: Tice = −20 °C, Bn (blue); Tice = −20 °C, Bf (purple); Tice = −20 °C, Bh (pink); Tice = −10 °C, Bn (black); Tice = −5 °C, Bn (red). Solid lines represent the fitted power-law relationships as per Eq. (1). The dashed line represents retreat rates implemented in DeConto and Pollard, with the light grey dashes denoting the maximum retreat rate implemented. Inset: Residuals of power-law fit to retreat rates associated with simulated ice-cliff failure events, with color coding the same as the main plot.
Fig. 3
Fig. 3. Modes of structural failure dominated by shear-band formation.
Shear localization is observed in HiDEMbe (the brittle-elastic version of the Helsinki Discrete Element Model) simulations if, given ice-cliff height (Hc), inter-particle beam widths are sufficiently narrow (a) or the ice is sufficiently weak and damaged (b). Damage is represented by porosity (the percentage of pre-broken bonds). c Surface slumping and waterline bulging resulting from visco-elastic deformation simulated in the viscous mode of HiDEMve. d Vertical crevasses and calving via outward buoyant block rotation at a relatively thin glacier with substantial sliding (f = 10−5), as simulated using the intermediate elastic-brittle and viscous mode of HiDEMve. e Crevassing, shear bands, slumping and mélange growth were observed as thickness and friction increased (f = 10−4) using the same intermediate mode of HiDEMve as in d). Details on f are included in Supplementary Note 7. H = calving face thickness. Blue and white transparent planes represent the waterline.
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