In the present study we used the first rock glacier inventory for the entire French Alpsto model spatial permafrost distribution in the region. Climatic and topographic dataevaluated at the rock ...glacier locations were used as predictor variables in a GeneralizedLinearModel.Model performances are strong, suggesting that, in agreement with severalprevious studies, this methodology is able to model accurately rock glacier distribution. Amethodology to estimate model uncertainties is proposed, revealing that the subjectivityin the interpretation of rock glacier activity and contours may substantially bias the model.Themodel highlights a North-South trend in the regional pattern of permafrost distributionwhich is attributed to the climatic influences of the Atlantic and Mediterranean climates.Further analysis suggest that lower amounts of precipitation in the early winter and athinner snow cover, as typically found in the Mediterranean area, could contribute tothe existence of permafrost at higher temperatures compared to the Northern Alps. Acomparison with the Alpine Permafrost Index Map (APIM) shows no major differenceswith our model, highlighting the very good predictive power of the APIM despite itstendency to slightly overestimate permafrost extension with respect to our database. Theuse of rock glaciers as indicators of permafrost existence despite their time response toclimate change is discussed and an interpretation key is proposed in order to ensure theproper use of the model for research as well as for operational purposes.
Abstract Cryospheric long-term timeseries get increasingly important. To document climate-related effects on long-term viscous creep of ice-rich mountain permafrost, we investigated timeseries ...(1995–2022) of geodetically-derived Rock Glacier Velocity (RGV), i.e. spatially averaged interannual velocity timeseries related to a rock glacier (RG) unit or part of it. We considered 50 RGV from 43 RGs spatially covering the entire European Alps. Eight of these RGs are destabilized. Results show that RGV are distinctly variable ranging from 0.04 to 6.23 m a −1 . Acceleration and deceleration at many RGs are highly correlated with similar behaviour over 2.5 decades for 15 timeseries. In addition to a general long-term, warming-induced trend of increasing velocities, three main phases of distinct acceleration (2000–2004, 2008–2015, 2018–2020), interrupted by deceleration or steady state conditions, were identified. The evolution is attributed to climate forcing and underlines the significance of RGV as a product of the Essential Climate Variable (ECV) permafrost. We show that RGV data are valuable as climate indicators, but such data should always be assessed critically considering changing local factors (geomorphic, thermal, hydrologic) and monitoring approaches. To extract a climate signal, larger RGV ensembles should be analysed. Criteria for selecting new RGV-sites are proposed.
Alpine mountains are affected by significant geomorphological processes whose evolution is partly conditioned by permafrost warming: rockfalls of various volumes, destabilisation of rock glaciers, ...and cryokarst. These phenomena, because of their intensity, may generate risks for territories. This paper provides a synthesis of the knowledge about the current status of the mountain permafrost in the French Alps and its recent evolution. This state-of-the-art overview is based on research conducted over the past 10 years and the measurements collected within PermaFRANCE, the French network for long-term observation of the mountain permafrost. The analysis of the available data shows that for a rock wall located at 3800 m asl., the temperature is between -4.5 and -1.5°C at a depth of 10 m, according to the aspect, whereas it is close to the melting point in surficial deposits at 2800 m asl. on a northern slope. Since the beginning of these measurements at depth in 2010, a trend of increasing temperature has been discernible, as found in other alpine boreholes. As clearly shown by the surface measurements conducted since 2003, the thermal regime is influenced by snow, particularly in surficial deposits and to a much lesser extent in rock walls. This inter-annual variability is combined with longer-term trends, which probably induce the observed changes in geomorphological dynamics associated with alpine permafrost: an increased frequency of gravitational processes such as rockfalls and fluctuation in rock glacier velocities. The possible increase in extreme events, such as rock avalanches or the destabilisation of rock glaciers, in the coming decades could create new or increased risks, to which territories must thus adapt.
In this study, we propose a methodology to estimate the spatial
distribution of destabilizing rock glaciers, with a focus on the French Alps.
We mapped geomorphological features that can be typically ...found in cases of
rock glacier destabilization (e.g. crevasses and scarps) using orthoimages
taken from 2000 to 2013. A destabilization rating was assigned by taking into
account the evolution of these mapped destabilization geomorphological
features and by observing the surface deformation patterns of the rock
glacier, also using the available orthoimages. This destabilization rating
then served as input to model the occurrence of rock glacier destabilization
in relation to terrain attributes and to spatially predict the
susceptibility to destabilization at a regional scale. Significant evidence
of destabilization could be observed in 46 rock glaciers, i.e. 10 % of the
total active rock glaciers in the region. Based on our susceptibility model
of destabilization occurrence, it was found that this phenomenon is more
likely to occur in elevations around the 0 ∘C isotherm (2700–2900 m a.s.l.),
on north-facing slopes, steep terrain (25 to 30∘) and flat to slightly
convex topographies. Model performance was good (AUROC = 0.76), and the
susceptibility map also performed well at reproducing observable patterns of
destabilization. About 3 km2 of creeping permafrost, or 10 % of the
surface occupied by active rock glaciers, had a high susceptibility to
destabilization. Considering we observed that only half of these areas of
creep are currently showing destabilization evidence, we suspect there is a
high potential for future rock glacier destabilization within the French
Alps.
The past four decades have seen extensive development of the winter sport industry in the French Alps and several hundred ropeway transport systems have been installed in areas where mountain ...permafrost may be present. Due to current climatic change and the ensuing permafrost degradation, the vulnerability of these infrastructures to destabilization may increase. Therefore, there is a real potential for instabilities to develop on ropeway transport systems in the Alps, requiring a better understanding of these processes. This study investigates the relation between permafrost and infrastructure stability in the French Alps, seeking to understand the evolution of this phenomenon over the past decades. This was done by following a two-step analysis. At first, the infrastructure elements built on modeled permafrost-affected areas were inventoried at the scale of the French Alps in order to get an overview of the possible vulnerabilities. Then, our study presents a detailed historical inventory of damage to infrastructure over the past three decades in different geomorphologic contexts. Overall, in the French Alps, there are almost 1000 infrastructure elements located in permafrost areas among which 12 (i.e., 24 infrastructure elements) were identified to have been subject to repeated instances of disruption and deterioration and most of the damages recorded were in areas where permafrost degradation is fully expected (ice-rich terrain). Infrastructure recovery costs may be significantly high, making this issue a relevant consideration to be included in the design process.
Abstract
Rock glaciers—ice-rich creeping landforms typical of permafrost mountain ranges—can develop an anomalous landslide-like behaviour called destabilisation. This behaviour is characterised by ...failure mechanisms (including cracks and crevasses) and increases in displacement rates by one to two orders of magnitude. Existing studies of this phenomenon have been limited to a small number of landforms and short time spans. Here, we systematically investigate the evolution of rock glacier kinematics over the past seven decades for the entire French Alps by combining observations of landform features indicative of the onset of destabilisation with data on displacements rates using aerial orthoimagery. We show that rock glacier velocities have significantly increased since the 1990s, concurrent with the development of destabilisation in 18 landforms that represent 5% of the 337 active rock glaciers. This pattern of activity correlates with rising air temperatures in the region, which suggests that a warming climate may play a role in this process.
PDF
