Olivier Gagliardini

Coupling of ice‐shelf melting and buttressing is a key process in ice‐sheets dynamics

[1]xa0Increase in ice-shelf melting is generally presumed to have triggered recent coastal ice-sheet thinning. Using a full-Stokes finite element model which includes a proper description of the grounding line dynamics, we investigate the impact of melting below ice shelves. We argue that the influence of ice-shelf melting on the ice-sheet dynamics induces a complex response, and the first naive view that melting inevitably leads to loss of grounded ice is erroneous. We demonstrate that melting acts directly on the magnitude of the buttressing force by modifying both the area experiencing lateral resistance and the ice-shelf velocity, indicating that the decrease of back stress imposed by the ice-shelf is the prevailing cause of inland dynamical thinning. We further show that feedback from melting and buttressing forces can lead to nontrivial results, as an increase in the average melt rate may lead to inland ice thickening and grounding line advance.

Ice microstructure and fabric: an up to date approach for measuring textures

Automatic c-axes analyzers have been developed over the past few years, leading to a large improvement in the data available for analysis of ice crystal texture. Such an increase in the quality and quantity of data allows for stricter statistical estimates. The current textural parameters, i.e. fabric (crystallographic orientations) and microstructure (grain-boundary networks), are presented. These parameters define the state of the polycrystal and give information about the deformation undergone by the ice. To reflect the findings from automatic measurements, some parameter definitions are updated and new parameters are proposed. Moreover, a MATLAB® toolbox has been developed to extract all the textural parameters. This toolbox, which can be downloaded online, is briefly described.

Estimating the risk of glacier cavity collapse during artificial drainage: The case of Tête Rousse Glacier

[1]xa0During the summer of 2010, the presence of a pressurized water-filled subglacial-cavity of at least 50,000 m3 was detected within the Tete Rousse Glacier (French Alps). Artificial drainage was started to avoid an uncontrolled rupture of the ice dam, but was interrupted soon after to evaluate the capacity of the cavity-roof to bear itself. The risk was that the release of pressure within the cavity during the artificial drainage would precipitate the collapse of the cavity roof and potentially flush out the remaining water flooding the valley below. An unprecedented modeling effort was deployed to answer the question of the cavity roof stability. We set up a model of the glacier with its water cavity, solved the three-dimensional full-Stokes problem, predicted the upper surface and cavity surface displacements for various drainage scenarios, and quantified the risk of the cavity failure during artificial drainage. We found that the maximum tensile stress in the cavity roof was below the rupture value, indicating a low risk of collapse. A post drainage survey of the glacier surface displacements has confirmed the accuracy of the model prediction. This practical application demonstrates that ice flow models have reached sufficient maturity to become operational and assist policy-makers when faced with glaciological hazards, thus opening new perspectives in risk management of glacier hazards in high mountain regions.

Constitutive Modelling and Flow Simulation of Anisotropic Polar Ice

The different approaches explored by the authors to model the visco-plastic anisotropic behaviour of polar ice associated with the formation and evolution of fabrics, are reviewed. In order to achieve ice rheological models which can significantly improve the simulations of the evolution of ice sheets under varying climatic conditions, these models aim at taking into account the physical mechanisms likely to be active under the conditions prevailing in an ice sheet. Since the destination of a constitutive model for polar ice is its implementation into a large scale ice-sheet model, which is to be run extensively to simulate various climatic scenarios, some compromises must be made to limit its complexity. A possible solution is to use a hierarchy of models of increasing complexity. In this respect the results from the different models are compared and discussed from the viewpoint of ice-sheet flow modelling.