The impact of temperature and crystal orientation fabric on the dynamics of mountain glaciers and ice streams
In the first Elmer/Ice contribution from the University of Maine, M.S. student Kate Hruby explored how the strength, orientation, and distribution of temperature and crystallographic fabric in streaming ice affects the bulk volumetric flux. This work derives from a larger project, run by Chris Gerbi, Seth Campbell, Karl Kreutz, Peter Koons, and Bob Hawley, to measure fabric, temperature, and strain in the lateral margin of a glacier and relate the observed and model systems. Although shear margins have long been recognized as important mechanical factors in streaming ice flux, they have been the focus of very few rheological observations and model investigation.
This study uses the AIFlow solver plus new solvers written by Carlos Martín that permit node-scale control of temperature and fabric distribution. The main findings of the study are that flux is moderately to highly sensitive to both temperature and pressure and that the distribution of these parameters is as significant as their magnitude. Thus, calculating or predicting the fluxes to the precision we expect is needed in most studies will require that both temperature and fabric be incorporated into models. That, in turn, will require more extensive observations of natural systems.
The paper abstract is: Streaming ice accounts for a major fraction of global ice flux, yet we cannot yet fully explain the dominant controls on its kinematics. In this contribution, we use an anisotropic full-Stokes thermomechanical flow solver to characterize how mechanical anisotropy and temperature distribution affect ice flux. For the ice stream and glacier geometries we explored, we found that the ice flux increases 1–3% per °C temperature increase in the margin. Glaciers and ice streams with crystallographic fabric oriented approximately normal to the shear plane increase by comparable amounts: an otherwise isotropic ice stream containing a concentrated transverse single maximum fabric in the margin flows 15% faster than the reference case. Fabric and temperature variations independently impact ice flux, with slightly nonlinear interactions. We find that realistic variations in temperature and crystallographic fabric both affect ice flux to similar degrees, with the exact effect a function of the local fabric and temperature distributions. Given this sensitivity, direct field-based measurements and models incorporating additional factors, such as water content and temporal evolution, are essential for explaining and predicting streaming ice dynamics.
Read more: Hruby, K., C. Gerbi, P. Koons, S. Campbell, C. Martín and R. Hawley, 2020. The impact of temperature and crystal orientation fabric on the dynamics of mountain glaciers and ice streams, Journal of Glaciology, doi:10.1017/jog.2020.44
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