Buoyant forces promote tidewater glacier iceberg calving through large basal stress concentrations
Iceberg calving parameterisations currently implemented in ice
sheet models do not reproduce the full observed range of calving behaviours.
For example, though buoyant forces at the ice front are known to trigger
full-depth calving events on major Greenland outlet glaciers, a multi-stage
iceberg calving event at Jakobshavn Isbræ is unexplained by existing
models. To explain this and similar events, we propose a notch-triggered
rotation mechanism, whereby a relatively small subaerial calving event
triggers a larger full-depth calving event due to the abrupt increase in
buoyant load and the associated stresses generated at the ice–bed interface.
We investigate the notch-triggered rotation mechanism by applying a
geometric perturbation to the subaerial section of the calving front in a
diagnostic flow-line model of an idealised glacier snout, using the
full-Stokes, finite element method code Elmer/Ice. Different sliding laws
and water pressure boundary conditions are applied at the ice–bed interface.
Water pressure has a big influence on the likelihood of calving, and stress
concentrations large enough to open crevasses were generated in basal ice.
Significantly, the location of stress concentrations produced calving events
of approximately the size observed, providing support for future application
of the notch-triggered rotation mechanism in ice-sheet models.
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