Modes of deformation in ice in dynamic regions: applications to basal crevasses and calving
Curry-Logan, Elizabeth Stacia
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Calving remains one of the most important yet unresolved aspects of glacier and ice sheet flow. Providing better constraints on global mean sea level rise will depend on our ability to simulate the dynamic flow of ice as it is discharged into the oceans. The work of this dissertation focuses on the important role basal crevasses play in the discharge of ice from glaciers and ice streams and how we can better model the formation and development of these features, particularly with regard to ice rheology during failure. First we make use of a large amount of ice penetrating radar data to image and understand the geometry and location of these features along the grounding line of the Siple Coast, in Antarctica. These data motivate the use of a thin-elastic beam approximation to the stresses that promote failure there, and the model is applied to all grounding lines across Antarctica, producing order-of-magnitude predictions where basal crevasses have already been observed. The simplicity of this model leads to the development of a more complex numerical model capable of visco-elasto-plastic simulation, DynEarthSol3D (DES), which performs the only time-dependent benchmark test designed for higher-order Stokes models. DES performs reasonably well against purely viscous numerical models and executes several experiments with idealized geometries exploring the roles that ice thickness and grounding line curvature play in the formation of basal crevasses in elastoplastic ice. Finally, with the implementation of a ductile-brittle transition zone based on longitudinal strain rate, we model the development of grounding line basal crevasses using visco-elasto-plastic rheology. Here we explore the roles that ice thickness and basal melting play in the formation and development of basal crevasses in ice as it is advected from resting on bedrock to floating in the ocean. We find that the inclusion of an extra measure of weakening to simulate the infiltration of buoyant ocean water in the basal crevasses is a crucial mechanism in developing the failure pattern seen in the floating portions of Thwaites Glacier and other glaciers around the world. The features that we simulate are truly semi-brittle, in that they require both viscous and elastic components of stress and a failure mechanism to develop.