Slliding of Glaciers and Subglacial water pressure – SAUSSURE

Glacier basal sliding largely sets glacier dynamics, and thus the advection of ice towards warmer areas with faster melt. Our lack of knowledge on the physics of basal sliding is such that we are unable to discriminate which physical law to use in large scale models, which causes large uncertainties in predictions of glacier retreat and sea level rise. Numerous studies have pointed out that our knowledge on basal sliding physics is mainly limited by lacking subglacial observations. The objective of the SAUSSURE project is to acquire key observations of subglacial physical processes and develop dedicated modelling frameworks in order to evaluate, improve, propose and validate friction laws in a natural, geophysical scale configuration.

To reach our goal, we will proceed in two steps. First, we will elaborate an advanced field measurement methodology on the Argentière Glacier (Mont Blanc area, France) in which we will overcome traditional observational difficulties and measure, simultaneously and at relevant spatio-temporal scales the key physical variables of interest. The Argentière Glacier is particularly suited for this investigation because it offers unique instrumentation possibilities thanks to easy access and to subglacial tunnels drilled into bedrock allowing acquiring observations with unique spatio-temporal coverage and definition (from the meso-scale of meters to tens of meters up to the glacier scale of hundreds of meters to few kilometers). This newly acquired dataset is ideally completed by a unique multi-decade-long dataset covering a time period of large changes in basal shear stress conditions that are crucial for fully testing basal friction laws.
Second, we will elaborate a thorough theoretical and modelling strategy to quantitatively test existing and if needed propose new basal friction laws based on our observations. The control of each physical process and parameters on basal sliding will be evaluated at multiple temporal scales (hours to decades), on one hand at the meso spatial scale at which friction laws are defined, and on the other hand at the glacier scale using large scale observational constraints on subglacial hydrology and long term observational constraints on glacier dynamics and mass balance.

In fine we anticipate demonstrating, we believe for the first time, whether and to which extent theoretical descriptions generally applied to a wide range of glaciers worldwide hold in a real setting. We are aware that our scientific findings obtained for a hard bedrock of an Alpine glacier will by construction not be generic, and thus not necessarily directly applicable to all glaciers around the world. Nevertheless, this work will provide evidences as to why and in which context certain types of glacier basal friction theories and formulations hold or not, giving the scientific community new clues about which friction laws are best suited to be applied globally for sea level rise and/or natural risk applications.

The SAUSSURE consortium possesses a strong experience in field measurements on glaciers, data analysis and ice flow modelling with the open-source finite-element model Elmer/Ice. The SAUSSURE project will provide a dataset which will be made available in a comprehensive form for the international community through relevant depositories, and will give the opportunity for the consortium to, in future projects, export the herein proposed innovative field measurement methods to other glaciers.