Dynamic Recrystallization in Ice
Overview
Dynamic recrystallization is particularly activated in regions of rapid deformation (that is, in fast-flowing ice streams), though it is rarely explicitly considered in ice-flow modeling. I am interested in understanding the effect that these processes have on the flow and fracture of ice.
Figure 1
I develop a model for steady-state grain size to consider the effect that grain size evolution has on the flow and fracture of ice. (a) I find that in zones of rapid deformation, recrystallization results in large grain sizes. This is due to a mechanism called migration recrystallization, which causes grain boundaries to migrate outwards in response to the build-up of elastic strain energy (the upside-down T’s represent dislocations, and a build-up of dislocations increases strain energy). (b) When applied to an actual glacier, like Pine Island Glacier, this means that in the margins of glaciers, grain sizes are likely large. As grain sizes grow, the strength of a material decreases, and so the grain growth in Pine Island Glacier translates to a ~75% decrease in the strength of the glacial ice. This may explain the observation that many fractures initiate in the margins of glaciers and then propagate to cause large calving events. This work may help explain how glaciers in Antarctica are losing mass.
Figure 2
To accurately model the effect of deformation on ice flow, we must consider the importance of dynamic recrystallization. Here, I show a graphic of the energy conversions that occur when glaciers deform rapidly to show that, while traditionally only thermal energy is taken into account, elastic strain and surface energy may play a large role. This suggests that ice flow models are missing key mechanisms that may affect the speed of ice flow and may be overestimating the rate of thermal energy production by assuming that only thermal energy changes occur.
Related Publications
[1] Ranganathan, M., Minchew, B., Meyer, C., & Pec, M. Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves, accepted, doi:10.31223/X5W31W.
[2] Ranganathan, M., Minchew, B., Meyer, C., & Pec, M. Deformational energy partitioning in glacier shear zones, submitted, doi:10.1002/essoar.10507633.1.