Abstract
Abstract. There are on average 35 fatal mountaineering accidents per summer in France. On average, since 1990, 3.7 of them have occurred every summer in the Grand Couloir du Goûter, on the classic route up Mont Blanc (4809 m a.s.l.). Rockfall is one of the main factors that explain this high accident rate and contribute to making it one of the most accident-prone areas in the Alps for mountaineers. In this particular context, the objective of this study is to document the rockfall activity and its triggering factors in the Grand Couloir du Goûter in order to disseminate the results to mountaineers and favour their adaptation to the local rockfall hazard. Using a multi-method monitoring system (five seismic sensors, an automatic digital camera, three rock subsurface temperature sensors, a traffic sensor, a high-resolution topographical survey, two weather stations and a rain gauge), we acquired a continuous database on rockfalls during a period of 68 d in 2019 and some of their potential triggering factors (precipitation, ground and air temperatures, snow cover, frequentation by climbers). At the seasonal scale, our results confirm previous studies showing that rockfalls are most frequent during the snowmelt period in permafrost-affected rockwalls. Furthermore, the unprecedented time precision and completeness of our rockfall database at high elevation thanks to seismic sensors allowed us to investigate the factors triggering rockfalls. We found a clear correlation between rockfall frequency and air temperature, with a 2 h delay between peak air temperature and peak rockfall activity. A small number of rockfalls seem to be triggered by mountaineers. Our data set shows that climbers are not aware of the variations in rockfall frequency and/or cannot/will not adapt their behaviour to this hazard. These results should help to define an adaptation strategy for climbers. Therefore, we disseminated our results within the mountaineering community thanks to the full integration of our results into the management of the route by local actors. Knowledge built during this experiment has already been used for the definition and implementation of management measures for the attendance in summer 2020.
Highlights
Despite a growing body of scientific literature, several international entities such as the World Meteorological Organization (WMO), the Intergovernmental Panel on Climate Change (IPCC) and the Mountain Research Initiative (MRI) agree that there is a profound lack of knowledge of the vulnerability of socio-economic activities to climate change in Published by Copernicus Publications on behalf of the European Geosciences Union.J
We found a clear correlation between rockfall frequency and air temperature, with a 2 h delay between peak air temperature and peak rockfall activity
Period 1 covers the first half of the season (29 June to 30 July, i.e. 32 d), which is characterised by the highest rockfall frequency (1916 events, i.e. 1 rockfall every 24 min)
Summary
Despite a growing body of scientific literature, several international entities such as the World Meteorological Organization (WMO), the Intergovernmental Panel on Climate Change (IPCC) and the Mountain Research Initiative (MRI) agree that there is a profound lack of knowledge of the vulnerability of socio-economic activities to climate change in Published by Copernicus Publications on behalf of the European Geosciences Union.J. The climbing parameters – technical difficulty, level of exposure to natural hazards and optimal periods for climbing – of the classic mountaineering route up Mont Blanc (4809 m a.s.l., Mont Blanc massif – MBM – France), undoubtedly one of the most popular in the world (200 000 passages per year; Mourey and Ravanel, 2017), have significantly changed because of the effects of climate change (Mourey et al, 2019) This evolution is mostly related to an increasing number of rockfalls on the west face of the Aiguille du Goûter (3863 m a.s.l.), which includes the crossing of the Grand Couloir du Goûter and the ascent of the Goûter rock ridge (“arête du Goûter”) leading to the Goûter refuge located at 3835 m a.s.l. According to Magnin et al (2015), this sector is located in a context of permafrost – any lithospheric material with a temperature remaining below or at 0 ◦C for at least 2 years (NRCC, 1988; Van Everdingen, 1998; Fig. 1)
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