Velocity estimation of Grandes Jorasses glacier in the framework of GlaRiskAlp project

The Grandes Jorasses hanging glacier, located at 4100 m asl above a populated area, is monitored by Fondazione Montagna sicura since 2007, on account of the Geological Service of the Aosta Valley Autonomous Region. The serac dynamic shows a periodic trend of mass increasing, interrupted by a collapse: The collapse is preceded by an exponential acceleration that lasts few days, as revealed in 1997-98 by Prof. M Funk (ETH Zurich). By tracking the velocity of the ice mass it is therefore possible to forecast its breakdown. At the early stage of the project the native monitoring system consisted of poles with prisms placed on the glacier surface, monitored by an automatic total station (motorized total station) sited at the valley bottom. During bad weather conditions the system could loss measurements, so alternative monitoring systems were designed, installed and tested in the framework of the GlaRiskAlp project (Alcotra program). In particular the new monitoring systems consisted of a low cost, single frequency, GNSS wireless sensors network, able to trace continuously (H24) the receivers positions to measure the displacement in real time, and a seismometer at the top of the glacier was placed in order to follow the seismic activity (that is proportional to the velocity). Furthermore, in order to better characterize the mass evolution, photogrammetric activities were carried out to reconstruct the glacier surface. Prototypes, results and outlooks of these monitoring systems for Grandes Jorasses glacier will be presented.