The 2006 Collapse of the Berard Rock Glacier (Southern French Alps)

In the Mediterranean French Alps, the Berard rock glacier suddenly collapsed during the summer of 2006; this was a rarely documented event in the world, exceptional for the amount of disturbed material (estimated at 250 000-500 000 m(3)). Located near the lower limit of permafrost, the Berard rock glacier collapse might exemplify the possible consequences of the degradation of ice-rich mountain permafrost. The causes of the collapse may include long-term atmospheric warming, recent air temperature anomalies, niveo-meteorological conditions prior to the collapse, geological settings and topographical context. Geomorphological interpretations and analysis of climatic data-sets allow us to specify the different stages of the collapse and discuss the respective roles of the geological and hydro-climatic factors and unfrozen water in the ground which could have led to the collapse. Geophysical measurements and ice observations in the scarp reveal that the internal structure of the intact part of the rock glacier is composed of both ice-cemented and massive-ice layers. The rock glacier also contains a high proportion of fine material (essentially silt and clay), which could have played an important role in the collapse. Geodetic measurements repeated since 2007 show that, with the exception of the upper part, the whole rock glacier was still experiencing destabilisation in 2010, with very high deformation rates exceeding 30 m in 3 years. The continuous monitoring of surface displacement carried out during the summer of 2007 has not shown any clear meteorological control on the post-collapse rock glacier dynamics. Copyright (c) 2016 John Wiley & Sons, Ltd.