Comparison of exposure ages and spectral properties of rock surfaces in steep, high alpine rock walls of Aiguille du Midi, France

Abstract

Among various factors, permafrost and frost-thaw cycles play an important role for the stability of steep rock slopes in high alpine regions. Climate change in general and local temperature and precipitation trends in particular are likely to influence permafrost and, consequently, also the stability of rock walls. As stress relief following deglaciation can be excluded at Aguille du Midi (France), rockfall activity is mainly related to changes in permafrost and frost-thaw cycles. To put modern observations of possible climate-induced rockfalls into perspective, information on past rockfall activity is required. In this study, we investigated a combination of surface exposure dating and spectrometry to derive a correlation between rock surface ages and their spectral properties in homogenous lithology. The surface ages found varied from less than 2,000 years to around 40,000 years, and showed a clear correlation with reflectance behavior in the range 380–580 nm. These results may be a first step towards the possible generation of spatial data fields of age distribution in steep rock walls. This may provide deeper insights into spatial and temporal rock-wall development of permafrost in high alpine permafrost environments.