Preprints
https://doi.org/10.5194/egusphere-2024-3067
https://doi.org/10.5194/egusphere-2024-3067
18 Oct 2024
 | 18 Oct 2024
Status: this preprint is open for discussion.

A comparative study of fabric evolution models and anisotropic rheologies

Daniel H. Richards, Elisa Mantelli, Samuel S. Pegler, and Sandra Piazolo

Abstract. Ice is anisotropic, with its viscosity varying by an order of magnitude in different directions when ice crystals align. However, how this variation affects ice flow is not well understood. This is because of a lack of a) models for fabric (the collective distribution of crystal orientations) evolution accurate enough to reproduce observations, and b) knowledge of which anisotropic rheology is most appropriate. Here we address both these problems. First, we review a range of previous models for fabric evolution and show they can be combined into a common differential equation. This incorporates a handful of parameters and an anisotropic rheology, which can be freely chosen. We apply this model, with a range of different anisotropic rheologies, to both an ice stream and an ice divide. For each rheology we choose the parameters to give the best possible fit to observations. We find these parameters are significantly different from those used previously. Best results come from assuming the grains rotate due to stress rather than deformation, with the stress calculated through an anisotropic rheology. By including grain rotation primarily due to stress, combined with a diffusion of the fabric, we can reproduce observations at both an ice divide and, for the first time, at an ice stream. We also compare and rank a range of anisotropic rheologies based on the accuracy of their fabric predictions. The rheologies which give the closest fit to observations have a tensor description of the anisotropy and assume that neighbouring ice grains experience approximately the the same stress.

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Daniel H. Richards, Elisa Mantelli, Samuel S. Pegler, and Sandra Piazolo

Status: open (until 29 Nov 2024)

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Daniel H. Richards, Elisa Mantelli, Samuel S. Pegler, and Sandra Piazolo
Daniel H. Richards, Elisa Mantelli, Samuel S. Pegler, and Sandra Piazolo

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Short summary
Ice behaves differently depending on its crystal orientation, but how this affects its flow is unclear. We combine a range of previous models into a common equation to better understand crystal alignment. We tested a range of previous models on ice streams and divides, discovering that the best fit to observations comes from a) assuming neighbouring crystals have the same stress, and b) through describing the effect of crystal orientation on the flow in a way that allows directional variation.