Rock falls in high-alpine rock walls quantified by terrestrial lidar measurements : A case study in the Mont Blanc area

International audience; The global warming observed in recent decades and its future increase may affect permafrost distribution on high-mountain faces with consequences for their stability. In this paper, we show that rock falls from high-alpine rock walls can be computed with a decimetre-resolution using lidar measurements. A laser scanner was used to create point clouds and triangulated irregular network models on the east face of the Tour Ronde at 3792 m asl (Mont Blanc massif). Comparison of the models realised from measurements of July 2005 and July 2006 enabled quantification of rock falls with reduced uncertainty. The volume of rock fall reached a total of 536 m3 in the scanned area, which matches an erosion rate of 8.4 mm yr−1. This rate slightly higher to the ones reported in former studies enable to assume that this rock fall may be the consequence of the permafrost degradation in this rock face.