A Rock Glacier Characterization - Bellecombes, Deux Alpes, France

Global warming caused pronounced effects on glacier and permafrost (subsurface materiel remaining below 0°C for at least two year). Temperature changes imply changes in mechanical properties of the permafrost and could increase hazard in Alpine environments. As these mechanicals properties changes can often not be detected from the surface, the anticipation of this hazard is difficult. Therefore geophysical surveys were performed to investigate a rock glacier body, one of the main indicators of permafrost. This work has two objectives. Firstly determining the thickness of the permafrost to estimate the ice quantity and monitoring its variations. Knowning the bedrock depth is also a main issue to resolve geotechnical problems. Secondly, finding methodology to determine the thickness of the active layer which is highly unstable in case of high precipitations. Investigations were carried out on the Bellecombes rock glacier (Isère, France). They were composed of borehole, electrical tomography profiles, seismic profiles for surface-wave inversions, H/V measurements, which are fast and easy to perform in the field, in order to image wave contrasts, and ground penetrating radar measurements. Results show that geophysical investigations improve knowledge of internal structure of rock glacier when they are combined with preliminary geomorphological study and boreholes.