Monitoring unstable parts in the ice-covered Weissmies northwest face

Lukas E Preiswerk, Fabian Walter, Sridhar Anandakrishnan, Giulia Barfucci, Jan Beutel, Peter G Burkett, Pierre Dalban Canassy, Martin Funk, Philippe Limpach, Emanuele Marchetti, Lorenz Meier and Fabian Neyer

The glacierized northwest face of Weissmies in the Saas valley (Switzerland) recently became unstable due to climate-induced glacier thinning of the supporting Triftgletscher below. In the case of a large break-off of ice, human infrastructure in the Saas valley is exposed to the danger of an ice/snow avalanche. A monitoring campaign was initiated with the goal of detecting precursory signals to the break-off. Interferometric and Doppler radar, optical imaging as well as GPS sensors provide measurements of surface displacements. Infrasound and seismometer arrays monitor acoustic and seismic emissions of ice avalanches and englacial fracture development. Here we discuss the monitoring methods and the results obtained so far. The unstable glacier mass did not undergo a large-scale break-off event, in fact it decelerated during the unusually warm summer months. An explanation remains elusive but likely involves subglacial processes and bedrock topography. Nevertheless, our results allow us to draw important conclusions regarding the suitability of different approaches to monitoring unstable glaciers.

2016/1 434-443