With Elmer/Ice among a multitude of models, including surface energy balance and runoff, a simple basal hydrological model as well as a plume and a discrete element model, the authors investigate the influence of undercutting caused by plumes fed by runoff entering the glacier and released at certain outlets by basal hydrological flowpaths as well as sliding on calving rates at Kronebreen, Svalbard. The authors are able to show the influence of undercutting as well as basal sliding on calving rates of this fast flowing tidewater. Sliding coefficients have been obtained from a temporal and spatial high resolution satellite data-set. Those obtained friction coefficients - as well as the geometry obtained from the undercut model and Elmer/Ice are used in the discrete element model HIDEM to simulate the calving behaviour, which then are compared to measured front positions.
Read more: Vallot, D., J. Åström, T. Zwinger, R. Pettersson, A. Everett, D.I. Benn, A. Luckman, W.J.J. van Pelt, F. Nick, and J. Kohler, 2018. Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard. The Cryosphere, 12, 609-625, doi:10.5194/tc-12-609-2018
Determining calving in continuum models - such as Elmer/Ice - is a challenge. In this latest paper, the authors present a full 3D calving model developed in Elmer/Ice, based on the crevasse depth criterion, which states that calving occurs when surface and basal crevasses penetrate the full thickness of the glacier. Alongside, a new 3D rediscretization approach and a time-evolution scheme which allow the calving front to evolve realistically through time have been implemented. The model is applied to the Store Glacier, one of the largest outlet glaciers in West Greenland. Results reveal that the new model realistically simulates the seasonal advance and retreat when two principal environmental forcings, namely submarine melting and ice mélange buttressing, are applied. The sudy clearly links ice mélange buttressing to Store Glacier's seasonal advance and retreat. Distributed submarine melting prevents the glacier from forming a permanent floating tongue, while concentrated plume melting has a disproportionately large and potentially destabilizing effect on the calving front position. Results further highlight the importance of basal topography, which exerts a strong control on calving. This explains why Store Glacier has remained stable during a period when neighboring glaciers have undergone prolonged interannual retreat.
Read more: Todd, J., P. Christoffersen, T. Zwinger, P. Råback, N. Chauché, D. Benn, A. Luckman, J. Ryan, N. Toberg, D. Slater, and A. Hubbard, 2018. A Full-Stokes 3D Calving Model applied to a large Greenlandic Glacier. Journal of Geophysical Research: Earth Surface. doi:10.1002/2017JF004349
We used a finite element model to interpret anti-correlated pressure variations at the base of a glacier to demonstrate the importance of stress redistribution in the basal ice. We first investigated two pairs of load cells installed 20 m apart at the base of the 210 m thick Engabreen glacier in Northern Norway. The load cell data for July 2003 showed that pressurisation of a subglacial channel located over one load cell pair led to anti-correlation in pressure between the two pairs. To investigate the cause of this anti-correlation, we used a full Stokes 3D model of a 210 m thick and 25–200 m wide glacier with a pressurised subglacial channel represented as a pressure boundary condition. The model reproduced the anti-correlated pressure response at the glacier bed and variations in pressure of the same order of magnitude as the load cell observations. The anti-correlation pattern was shown to depend on the bed/surface slope. On a flat bed with laterally constrained cross-section, the resulting bridging effect diverted some of the normal forces acting on the bed to the sides. The anti-correlated pressure variations were then reproduced at a distance >10–20 m from the channel. In contrast, when the bed was inclined, the channel support of the overlying ice was vertical only, causing a reduction of the normal stress on the bed. With a bed slope of 5 degrees, the anti-correlation occurred within 10 m of the channel. The model thus showed that the effect of stress redistribution can lead to an opposite response in pressure at the same distance from the channel and that anti-correlation in pressure is reproduced without invoking cavity expansion caused by sliding.
More information: Lefeuvre P.-M., T. Zwinger, M. Jackson, O. Gagliardini, G. Lappegard and J.O. Hagen, 2018. Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations. Front. Earth Sci. 5:110. doi:10.3389/feart.2017.00110