Abstract
Abstract. High alpine rock wall permafrost is extremely sensitive to climate change. Its degradation has a strong impact on landscape evolution and can trigger rockfalls constituting an increasing threat to socio-economical activities of highly frequented areas; quantitative understanding of permafrost evolution is crucial for such communities. This study investigates the long-term evolution of permafrost in three vertical cross sections of rock wall sites between 3160 and 4300 m above sea level in the Mont Blanc massif, from the Little Ice Age (LIA) steady-state conditions to 2100. Simulations are forced with air temperature time series, including two contrasted air temperature scenarios for the 21st century representing possible lower and upper boundaries of future climate change according to the most recent models and climate change scenarios. The 2-D finite element model accounts for heat conduction and latent heat transfers, and the outputs for the current period (2010–2015) are evaluated against borehole temperature measurements and an electrical resistivity transect: permafrost conditions are remarkably well represented. Over the past two decades, permafrost has disappeared on faces with a southerly aspect up to 3300 m a.s.l. and possibly higher. Warm permafrost (i.e. > − 2 °C) has extended up to 3300 and 3850 m a.s.l. in N and S-exposed faces respectively. During the 21st century, warm permafrost is likely to extend at least up to 4300 m a.s.l. on S-exposed rock walls and up to 3850 m a.s.l. depth on the N-exposed faces. In the most pessimistic case, permafrost will disappear on the S-exposed rock walls at a depth of up to 4300 m a.s.l., whereas warm permafrost will extend at a depth of the N faces up to 3850 m a.s.l., but possibly disappearing at such elevation under the influence of a close S face. The results are site specific and extrapolation to other sites is limited by the imbrication of local topographical and transient effects.
Highlights
The IPCC Fifth Assessment Report (AR5) has drawn a global increase in permafrost temperature since the 1980s (IPCC, 2014)
This last model has been applied on a 4 mresolution DEM of the French part and of the Swiss and Italian borders of the Mont Blanc massif with local air temperature input data to map the mean annual rock surface temperature (MARST; Figs. 1 and 2, Magnin et al, 2015a)
We run the transient simulations in the commercial hydrogeological software DHIWASY FEFLOW version 7.0 by forcing the RST with climate time series from 1850 to 2100 and solving the heat conduction equation in 2-D with consideration of freeze and thaw processes in the bedrock interstices
Summary
The IPCC Fifth Assessment Report (AR5) has drawn a global increase in permafrost temperature since the 1980s (IPCC, 2014). Haeberli et al (1997) identified various types of high mountain slope instabilities that could be prepared or triggered by interactive processes between bedrock, permafrost and glaciers Such processed have been largely observed, especially with the increase in rockfall activity of high-elevation permafrost rock walls during the past two decades (Ravanel and Deline, 2011). The increasing amount of available RST time series in the European Alps has permitted the formulation of such statistical model for the entire Alpine range (Boeckli et al, 2012) This last model has been applied on a 4 mresolution DEM of the French part and of the Swiss and Italian borders of the Mont Blanc massif with local air temperature input data to map the mean annual rock surface temperature We run the transient simulations in the commercial hydrogeological software DHIWASY FEFLOW version 7.0 by forcing the RST with climate time series from 1850 to 2100 and solving the heat conduction equation in 2-D with consideration of freeze and thaw processes in the bedrock interstices
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
