Elmer/Ice News

A new calving model in Elmer/Ice

krug2014

Calving of icebergs is a major negative component of polar ice-sheet mass balance. Here we present a new calving model relying on both continuum damage mechanics and linear elastic fracture mechanics. This combination accounts for both the slow sub-critical surface crevassing and the rapid propagation of crevasses when calving occurs. First, damage to the ice occurs over long timescales and enhances the viscous flow of ice. Then brittle fractures propagate downward, at very short timescales, when the ice body is considered as an elastic medium. The model was calibrated on Helheim Glacier, Southeast Greenland, a well-monitored glacier with fast-flowing outlet. This made it possible to identify sets of model parameters to enable a consistent response of the model and to produce a dynamic equilibrium in agreement with the observed stable position of the Helheim ice front between 1930 and today.

Krug, J., J. Weiss, O. Gagliardini and G. Durand, 2014. Combining damage and fracture mechanics to model calving, The Cryosphere, 8, 2101-2117, doi:10.5194/tc-8-2101-2014 [link to paper]

Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard

Various subglacial f06c noannonmechanisms have been suggested for fast flow but common to most of the suggested processes is the requirement of presence of liquid water, and thus temperate conditions. The authors  used  a  combination  of  modelling,  field,  and  remote observations in order to study links between different heat sources, the thermal  regime  and  basal  sliding  in fast  flowing areas on Vestfonna ice cap. Special focus was put on Franklinbreen, a fast flowing outlet glacier which has been observed to accelerate recently.  Elmer/Ice was utilized including a Weertman type sliding law and a Robin inverse  method  to  infer  basal  friction  parameters  from  observed surface velocities. Firn heating, i.e. latent heat release through percolation of melt water, is included in our model; its parameterisation is calibrated with the temperature record of a deep borehole. The authors found that strain heating is negligible, whereas friction heating is identified as one possible trigger for the onset of fast flow. Firn heating is a significant heat source in the central thick and slow flowing area of the ice cap and the essential driver behind the ongoing fast flow in all outlets.

Schäfer, M., Gillet-Chaulet, F., Gladstone, R., Pettersson, R., A. Pohjola, V., Strozzi, T., and Zwinger, T.: Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard, The Cryosphere, 8, 1951-1973, doi:10.5194/tc-8-1951-2014, 2014.

Elmer/Ice course in Hobart, Tasmania

Rupert Gladstone (This email address is being protected from spambots. You need JavaScript enabled to view it.) will be leading Elmer/Ice training at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) in Hobart from 12th to 14th November 2014.  This is primarily for Australian Antarctic Division (AAD) and University of Tasmania (UTas) staff, but guest places are available.  The course level will be introductory to intermediate, making use of material prepared by Thomas Zwinger, Olivier Gagliardini and Fabien Gillet-Chaulet for previous courses. For any further details, please contact Rupert.

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