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Bedrock permafrost is a feature of cold mountain ranges that was found responsible for the increase of rock fall and landslide activity in several regions across the globe. In Greenland, bedrock permafrost has received so far little attention from the scientific community, despite mountains are a predominant feature on the ice-free coastline and landslide activity is significant. With this study, we aim to move a first step towards the characterization of bedrock permafrost in Greenland. Our study area covers 100 km2 of mountain terrain around the town of Sisimiut – 68° N on the West Coast. We first acquire surface ground temperature data from 2020–2021 to model bedrock surface temperatures time series from weather forcing on the period 1850–2022. Using a topographical downscaling method based on digital elevation model, we then create climatic boundary conditions for 1D and 2D heat transfer numerical simulations at the landscape level. In this way we obtain permafrost distribution maps and ad-hoc simulations for complex topographies. Our results are validated by comparison with temperature data from two lowland boreholes (100 m depth) and geophysical data describing freezing/unfreezing conditions across a mid-elevation mountain ridge. Finally, we use regional carbon pathway scenarios 2.6 and 8.5 to evaluate future evolution of ground temperatures to 2100. Our results indicate a sporadic permafrost distribution up to roughly 400 m.a.s.l., while future scenarios suggest a decline of deep frozen bodies up to 800 m.a.s.l., i.e. the highest summits in the area.

International audience; In the current context of climate change, high Alpine rock slopes and surface deposits are affected by a series of geomorphological processes whose evolution is partly conditioned by permafrost warming and thawing. This degradation directly impacts infrastructure in high mountain areas (e.g., huts or ropeway transport systems). In this study, we aim to assess the level of risk of destabilization for infrastructure built on permafrost in the French Alps and to discuss the adaptation and mitigation strategies developed by stakeholders. The analysis combines an inventory of the high mountain infrastructure with several data layers-including two recently developed regional maps of permafrost-analysed within a Geographic Information System. We update a destabilization risk index previously developed to identify and rank infrastructure at risk with a hazard characterisation and a vulnerability diagnosis, based on newly available data. The most at-risk infrastructure according to this new risk index are compared with the strategies implemented by the stakeholders to adapt the foundation, reinforce the ground, reduce heat transfer in depth, or monitor the evolution of the ground. Most of the strategies used on the most at-risk cases are reactive to repair the infrastructure after a destabilization.

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.

In high alpine environments, climate change leads to an increase in rockfall destabilizations. They represent a threat for sports and tourism activities in high mountain and especially for mountaineering. This danger of rockfall is particularly important on the classic route up Mont Blanc (4,809 m a.s.l., Mont Blanc massif, France), on the west face of the Aiguille du Goûter (3,863 m a.s.l.), and is responsible for at least 29 % of the accidents that occur in this sector. Despite the intensity of the geomorphological processes at work and the vulnerability of climbers, few scientific studies have been carried out on the occurrence of rockfalls and their triggering factors in the Goûter area. Based on a multi-method monitoring system (5 seismic sensors, an automatic digital camera, 3 subsurface temperature sensors, a pyroelectric sensor, a high-resolution topographical survey, 2 weather stations and a rain gauge) the objective of our study is therefore to quantitatively document the occurrence of rockfalls and their triggering factors in the Grand Couloir du Goûter in order to better assess the vulnerability of mountaineers in this sector. Our results show that in the high-Alpine and permafrost-affected Aiguille du Goûter west face, rockfalls are mostly frequent during the snowmelt period which favors the action of thermo-mechanical processes linked to the infiltration of liquid water into the cracks of the rock. During periods when the couloir is completely clear of snow, rockfalls are 2.5 times less frequent, and the thermo-mechanical processes involved in the rockfall triggering are limited by the absence of moisture in the ground. These results also show that climbers' awareness of the risk of rockfalls remains limited. What’s more, they do not adapt – or only slightly – their behavior to this risk, despite a particularly high accident rate. Important work on prevention and dissemination of the knowledge here acquired (newsletters, training for professionals and amateurs, awareness campaigns) among mountaineers is therefore still really necessary.

International audience

The ongoing acceleration in rock glacier velocities concurrent with increasing air temperatures, and the widespread onset of rock glacier destabilization have reinforced the interest in rock glacier dynamics and in its coupling to the climate system. Despite the increasing number of studies investigating this phenomenon, our knowledge of both the fundamental mechanisms controlling rock glacier dynamics, and their long‐term behaviour at the regional scale remain limited. We present a general theory to investigate rock glacier dynamics, its spatial patterns and temporal trends at both regional and local scale. To this end, we combine a model to calculate rock glacier thickness with an empirical creep model for ice‐rich debris, in order to derive the Bulk Creep Factor (BCF), which allows to disentangle the two contributions to the surface velocities from (i) material properties and (ii) geometry. Thereafter, we provide two examples of possible applications of this approach at a regional and local scale.

International audience; On August 14 th 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three-week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast-moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization.

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.

International audience; In the Val Thorens ski resort (Savoie, France), more than 79 infrastructure elements related to ropeway transport systems are located on permafrost. During the last decade, three of them (two top stations and a pylon located around 3,000 m a.s.l.) experienced destabilization which required important adjustment and stabilization work. his study investigates the destabilization of the pylon #2 of the horens funitel that occurred during the Summer 2016. Its foundations were afected by horizontal displacement and subsidence, causing a metric shit of the pylon top with respect to the cable. he pylon was built on a rock glacier which morphology was severely altered by earth work aiming to develop a ski slope. A multidisciplinary analysis was conducted in order to understand the processes that led to the pylon destabilization with a focus on the role of the morphological alterations of anthropogenic origin on the rock glacier dynamic. We used (i) a stratigraphic data analysis from boreholes and (ii) a subsurface analysis based on geophysics (Electrical Resistivity Tomography proiles) to understand the rock glacier internal structure, while (iii) geomorphological surface modiications were investigated by comparing digital terrain models obtained by aerial photogrammetry before and ater the earthwork. his study highlights the preparatory role of the earthwork and a non-control of the surface water low in an ice-rich environment such as a rock glacier.; La station de Val horens (Savoie, France) concentre plus de 79 composantes de remontées mécaniques en contexte de permafrost probable. Au cours de la dernière décennie, trois d' entre elles (deux gares amont et un pylône), situées vers 3 000 m d'altitude, ont subi des déstabilisations partielles nécessitant d'importants travaux de confortement et de stabilisation. Cet article documente la déstabilisation du pylône n° 2 du funitel de horens au cours de l' été 2016. Ses fondations ont été afectées par un déplacement horizontal et un afaissement à l' origine d'un décalage métrique de la tête de pylône par rapport au câble. Le pylône en question est implanté sur un glacier rocheux terrassé dans le cadre de l'aménagement d'une piste de ski. Une analyse multi-méthode a été conduite ain d' évaluer le rôle du permafrost dans la déstabilisation et de caractériser l' évolution des processus ainsi que l'impact des modiications anthropiques sur la dynamique du glacier rocheux à travers (i) l'analyse stratigraphique de données de forages, (ii) une analyse du terrain porteur fondée sur des proils géophysiques de résistivité des matériaux acquis par tomographie électrique, et (iii) la reconstitution des modiications géomorphologiques de surface par comparaison de modèles numériques de terrain, obtenus par photogrammétrie numérique (images aériennes IGN et drone) avant et après terrassement. Cette étude met en évidence le rôle préparatoire du terrassement et des écoulements d' eau de surface mal contrôlés dans un milieu riche en glace tel qu'un glacier rocheux.

International audience

Knowing the extent of degrading permafrost is a key issue in the context of emerging risks linked to climate change. In the present study we propose a methodology to estimate the spatial distribution of this phenomenon, focusing on the French Alps. At first, using recent orthoimages (2000 to 2013) covering the study region, we mapped the geomorphological features that can be typically found in cases of rock glacier destabilization (e.g. crevasses and scarps). This database was then used as support tool to rate rock glaciers destabilization. The destabilization rating was assigned also taking into account the surface deformation patterns of the rock glacier, observable by comparing the orthoimages. The destabilization rating served as database to model the occurrence of destabilization in relation to terrain attributes and to predict the susceptibility to destabilization at the regional scale. Potential destabilization could be observed in 58 rock glaciers, i.e. 12 of the total active rock glaciers in the region. Potentially destabilized rock glaciers were found to be more prone to strong acceleration than stable rock glaciers within the period 2000–2013. Modelling the occurrence of destabilization suggested that this phenomenon is more likely to occur in elevations around the 0 °C isotherm (2700–2900 m.s.l.), on north-exposed, steep (up to 30°) and flat to slightly convex topographies. Model performances were good (AUROC: 0.76) and the susceptibility map reproduced well the observable patterns. About 3 km2 of creeping permafrost, i.e. 10 % of the surface occupied by active rock glaciers, had a high susceptibility to destabilization. Only half of this surface is currently showing destabilization evidence, suggesting that a significant amount of rock glaciers are candidates for future destabilization.

International audience; The accuracy of digital elevation models (DEMs) derived from structure-from-motion (SFM) multi-view stereo (MVS) 3D reconstruction is commonly computed for a single realization of model elevations. This approach may be adequate to estimate an overall measure of systematic error; however, it cannot provide a good estimation of measurement precision. Knowing measurement precision is crucial for measuring elevation surface changes observed by DEM comparisons. In this paper, we illustrate an approach to characterize spatial variation in the precision for SFM-MVS derived DEMs. We use a snow-covered surface of an active rock glacier located in the southern French Alps as the case study. A spatially varying precision estimate is calculated from repeated close-range aerial surveys for a single acquisition period by calculating the standard deviation per grid cell between the DEMs created for each flight repetition. Regression analysis using a generalized additive model (GAM) is performed to model the estimated precision and provide insights regarding how sensor, survey design and field site conditions may spatially influence the measurement precision. Additionally, we define how DEM error can be described differently depending on the available validation data. In our study image height above ground level and distance to ground control points had the greatest explanatory power for spatial variation in DEM precision. Image overlap, mean reprojection error and saturation were also useful for explaining spatially varying measurement precision of the DEMs. Field site characteristics, such as slope angle and shading, had the least importance in our model of precision. From a practical point of view, regression-modeled relationships between precision and image and site characteristics can be utilized to design future surveys with similar sensing platforms and site conditions for improved DEM precision.

International audience; 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.

International audience; Snow depth estimation derived from high-resolution digital elevation models (DEMs) can lead to improved understanding of the spatially highly heterogeneous nature of snow distribution, as well as help us improve our knowledge of how snow patterns influence local geomorphic processes. Slope deformation processes such as permafrost creep can make it challenging to acquire a snow-free DEM that matches the sub-snow topography at the time of the associated snow-covered DEM, which can cause errors in the computed snow depths. In this study, we illustrate how modelling changes in the sub-snow topography can reduce errors in snow depths derived from DEM differencing in an area of permafrost creep. To model the sub-snow topography, a surface deformation model was constructed by performing non-rigid registration based on B-splines of two snow-free DEMs. Seasonal variations in creep were accounted for by using an optimization approach to find a suitable value to scale the deformation model based on in-situ snow depth measurements or the presence of snow-free areas corresponding to the date of the snow-covered DEM. This scaled deformation model was used to transform one of the snow-free DEMs to estimate the sub-snow topography corresponding to the date of the snow-covered DEM. The performance of this method was tested on an active rock glacier in the southern French Alps for two surveys dates, which were conducted in the winter and spring of 2017. By accounting for surface displacements caused by permafrost creep, we found that our method was able to reduce the errors in the estimated snow depths by up to 33% (an interquartile range reduction of 11 cm) compared to using the untransformed snow-free DEM. The accuracy of the snow depths only slightly improved (root-mean-square error decrease of up to 3 cm). Greater reductions in error were observed for the snow depths calculated for the date that was furthest (i.e., the winter survey) in time from the snow-free DEM. Additionally, we found that our approach to scaling the deformation model has promising potential to be adapted for monitoring seasonal variations in permafrost creep by combining in-situ snow depth measurements with high-resolution surface deformation models.

International audience; long with a rising temperature trend registeredin the past decades along the European Alps, severalsignals of permafrost degradation have been reportedin the same region, e.g. rock glacier displacementacceleration and thickening of the active layer. Per-mafrost degradation is alarming due to its role in ter-rain destabilization and, in particular, ice-rich debrisslopes are of great concern due to their proximity toinhabited areas. Therefore, in the past years increas-ing efforts have been made either by the scientificcommunity and local authorities in understanding theprocesses and hazards linked to the alpine permafrostdegradation.The first step to manage the risk associated withpermafrost degradation is to know its spatial extent.Since alpine permafrost does not manifest itself on thesurface, exception made for rock glaciers, it is not suit-able for automatic mapping. Therefore distributionmodels are required to infer permafrost occurrence.Traditionally, permafrost distribution models take ad-vantage of rock glaciers as evidence of permafrostto extrapolate statistically its occurrence based oncorrelation with climate variables. Although severalstatistical models have been made at the whole alpinerange scale, only one permafrost distribution map,calibrated on the Combeynot massif and validated onthe Vanoise and Mercantour massifs, was designedspecifically for the French Alps. However, permafroststatistical modeling using rock glacier inventories hasbeen recognized to be biased depending on the datacharacteristics, making permafrost maps inaccurateat local scale when applied to specific areas. Thisis due to the fact that rock glaciers extents are notonly influenced by climate, but also by their dynam-ics, a complex function of local topography, geologyand ice content in the landform. Therefore, the valid-ity of current models in the French Alps is, at least,questionable.To address this issue, the service Restauration desTerrains en Montagne (RTM) in collaboration withthe Institut de Géographie Alpine (IGA) realized thefirst complete rock glacier inventory of the FrenchAlps. The inventory, which counts more than 2600features, spacing from the Mont Blanc Massif to theMediterranean Sea, represents an extremely valuablemodeling dataset. The present study aims to exploitthis inventory in order to assess permafrost distribu-tion in the French Alps. As a first step, the perform-ance of already existing models is evaluated. Rockglaciers are used as validation dataset and the modelsare tested for spatial bias, i.e. their performance isassessed in function of the area they are applied on.Then, a statistical model is specifically developedfor the French Alps. At first, the correlation betweenrock glaciers and geomorphological local parameters,as lithology and feeding area, is investigated by per-forming a statistical analysis. This allows to studyand model climate control on rock glaciers activityand boundaries, avoiding biases introduced by topo-graphic and geological local conditions. Climatic datainclude air temperature, solar radiation and precipita-tion. Due to the extent of area investigated, constantlapse rates are not applicable. In particular, geograph-ical gradients in air temperature and precipitation areinvestigated and spatial interpolation of observationsis performed.Different modeling strategies are investigated, com-pared and discussed. The rock glacier inventory ispartitioned to be used either as training and valida-tion dataset. Other data, as BTS and GST, are usedas validation where available. Finally, the model per-forming best on the validation set is selected. A landuse map is used to select debris covered areas on theFrench Alps and permafrost occurrence is modeled.The resulting permafrost distribution map is expectedto be a valuable decision support tool in permafrostdegradation related issues

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International audience; Permafrost-affected rockwalls can suffer from mechanical fatigue related to thermo-cryogenic processes. However, these processes, the rock slope kinematics, and the links between both remain largely unclear. This study reports five years of crackmeter measurements at 2-hours resolution from six of the main perennially ice-filled rock clefts at the Aiguille du Midi (3842 m a.s.l., Mont Blanc massif). Seasonal and inter-annual variations as well as response of fracture kinematics to thermo-cryogenic process are analyzed.

Inventoried in the French Alps and elsewhere in Europe, rock glaciers and alpine permafrost are being studied the more and more. According to the latest climate projections, it is estimated that the French Alps will be strongly affected by rising temperatures in the coming years. This could lead to an increased destabilization of active rock glaciers and to the unfolding of other risks related to this type of phenomena such as landslides and debris flows. During the last decades, several aerial images were taken on the French territory, which has allowed to carry out remote field analyses with the help of geomatics and remote sensing. In order to better understand the dynamics of destabilized rock glaciers during the last six decades, a study in the field of remote sensing has been carried out. The main objective of this study was to quantify the movement speed qrsztkof the "Roc Noir" rock glacier (in Vanoise) by using photogrammetric tools and aerial imagery processing tools to obtain 3D digital models and orthophotographs. Thus, in order to produce statistical and visual analyses of the site of study. The partial results of this methodology show that the kinematics of the rock glacier Roc Noir have changed a lot since the 1950's. The most important displacements were encountered between 2010 and 2013 followed by those between 2013 and 2017. Thanks to this analysis, it was possible to observe the movement of surface landforms associated with destabilized rock glaciers and to calculate a movement speed ranging from 0.9 meters per year (my-1) to 7.85 my-1 +/- 0.16my-1 on the Roc Noir surface. The downstream central area of the rock glacier showed a faster movement compared to the rest of its body. These figures have not been yet validated with field data; therefore, the reliability of these results is still uncertain. However, the orthophotos are very clear and reflect an accelerated evolution in recent decades.; Répertoriés dans les Alpes françaises et ailleurs en Europe, les glaciers rocheux et le pergélisol alpin sont de plus en plus étudiés. Selon les dernières projections climatiques, il est estimé que les Alpes françaises seront fortement affectées par l'augmentation des températures dans les années à venir, ce qui pourrait conduire à l’augmentation de la déstabilisation des glaciers rocheux actifs mais aussi des risques associés à ce type de phénomène tels quels les glissements de terrain et les laves torrentielles. Durant les dernières décennies, plusieurs images aériennes ont été prises sur le territoire français, ce qui permet à l’aide de la géomatique et de la télédétection de réaliser des analyses de terrain à distance. Afin de mieux comprendre la dynamique des glaciers rocheux déstabilisés au cours des six dernières décennies une étude dans le domaine de la télédétection a été réalisée. L’objectif principal de cette étude était de quantifier la vitesse de déplacement du glacier rocheux du Roc Noir (Vanoise) en employant des outils photogrammétriques et des traitements d’images aériennes afin d’obtenir des modèles numériques 3D et des orthophotos, pour ainsi réaliser des analyses statistiques et visuelles du site d’étude. Les résultats partiels de cette méthodologie montrent que la cinématique du glacier rocheux du Roc Noir a beaucoup changé depuis les années 1950, entre 2013 et 2017 mais surtout entre 2010 et 2013 où les déplacements ont été les plus importants. Grâce à cette analyse diachronique par photogrammétrie, il a été possible d’observer le mouvement des formes superficielles associées aux glaciers rocheux déstabilisés et de calculer des vitesses de déplacement du Roc Noir allant de 0.9 mètres par an (ma-1) jusqu’à 7.85ma-1 +/-0.16ma-1. La partie centrale en aval du glacier rocheux se déplaçant plus rapidement en comparaison au reste de son corps. Ces chiffres n’ont pas encore été validés avec des données de terrain, par conséquent la fiabilité de ces résultats est encore incertaine, par contre les orthophotos sont très claires et reflètent bien sa progression accélérée dans les dernières décennies.

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International audience; As evidenced by existing inventories, the semi-arid Andes (Chile and Argentina) has a high density of active rockglaciers and host some of the largest ones in the world. The movement of rock glaciers, which is crucial forunderstanding the effects of climate on mountain cryosphere, remains largely based on subjective interpretation ofgeomorphological signs visible on ortho-imagery. In order to get a regional assessment of rock glacier’s activity levels,we combined two type of satellite imagery, Synthetic Aperture Radar and optical. Both SAR-derived interferograms andmaps of displacement derived from optical image correlation were used to evaluate to mean activity level of more than200 active rock glaciers. Base on this, a geospatial analysis was performed to assess the main controlling factor on therock glaciers kinematic.

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