Rock glaciers throughout the French Alps accelerated and destabilised since 1990 as air temperatures increased

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

Application of Low-Cost UASs and Digital Photogrammetry for High-Resolution Snow Depth Mapping in the Arctic

The repeat acquisition of high-resolution snow depth measurements has important research and civil applications in the Arctic. Currently the surveying methods for capturing the high spatial and temporal variability of the snowpack are expensive, in particular for small areal extents. An alternative methodology based on Unmanned Aerial Systems (UASs) and digital photogrammetry was tested over varying surveying conditions in the Arctic employing two diverse and low-cost UAS-camera combinations (500 and 1700 USD, respectively). Six areas, two in Svalbard and four in Greenland, were mapped covering from 1386 to 38,410 m2. The sites presented diverse snow surface types, underlying topography and light conditions in order to test the method under potentially limiting conditions. The resulting snow depth maps achieved spatial resolutions between 0.06 and 0.09 m. The average difference between UAS-estimated and measured snow depth, checked with conventional snow probing, ranged from 0.015 to 0.16 m. The impact of image pre-processing was explored, improving point cloud density and accuracy for different image qualities and snow/light conditions. Our UAS photogrammetry results are expected to be scalable to larger areal extents. While further validation is needed, with the inclusion of extra validation points, the study showcases the potential of this cost-effective methodology for high-resolution monitoring of snow dynamics in the Arctic and beyond

Towards improved, cost-effective surveillance of Ixodes ricinus ticks and associated pathogens using species distribution modelling

Various ticks exist in the temperate hilly and pre-alpine areas of Northern Italy, where Ixodes ricinus is the more important. In this area different tick-borne pathogen monitoring projects have recently been implemented; we present here the results of a twoyear field survey of ticks and associated pathogens, conducted 2009-2010 in North-eastern Italy. The cost-effectiveness of different sampling strategies, hypothesized a posteriori based on two sub-sets of data, were compared and analysed. The same two subsets were also used to develop models of habitat suitability, using a maximum entropy algorithm based on remotely sensed data. Comparison of the two strategies (in terms of number of ticks collected, rates of pathogen detection and model accuracy) indicated that monitoring at many temporary sites was more cost-effective than monthly samplings at a few permanent sites. The two model predictions were similar and provided a greater understanding of ecological requirements of I. ricinus in the study area. Dense vegetation cover, as measured by the normalized difference vegetation index, was identified as a good predictor of tick presence, whereas high summer temperatures appeared to be a limiting factor. The study suggests that it is possible to obtain realistic results (in terms of pathogens detection and development of habitat suitability maps) with a relatively limited sampling effort and a wellplanned monitoring strategy

Déstabilisation des glaciers rocheux dans les Alpes Françaises : une évaluation à l'échelle régionale et locale

As occurring to several geosystems on our planet, mountain permafrost is threatened by climate change as prolonged warming may compromise the geotechnical properties of the frozen ground. As result, increasing occurrence of rockfall activity, thermokarst formation and rock glacier acceleration was observed in the past decades. Rock glacier destabilization, a process that compromises the structural integrity of these landforms, seems to be linked to atmospheric warming, gaining interest in the past years. The destabilization, which may be triggered by warming permafrost or mechanical stress, is characterized by an anomalous acceleration of the landform and the occurrence of specific features such as cracks and crevasses on its surface. Although the occurrence of these processes is mostly transitory, determining a textit{crisis} phase of the landform, in exceptional cases it may lead the rock glacier to structural collapse.This PhD thesis provided an assessment on the occurrence and related processes of rock glacier destabilization in the French Alps. At first, the spatial occurrence of debris permafrost was assessed in order to provide the permafrost distribution map of the French Alps, a tool that was necessary to evaluate permafrost conditions at rock glaciers sites. The second step consisted in an identification of destabilized rock glaciers in the region, which was done by multiple orthoimages interpretation aimed to identify features typically observable on destabilized rock glacier. Once identified the destabilized rock glaciers it was possible to analyse the typical topographical settings in which destabilization occurs and to to spot those landforms that are susceptible to experience this phenomenon. After these efforts at the regional scale, the focus was shifted towards local scale investigations at the Lou rock glacier, a partially destabilized landform that, due to frontal failure, in August 2015 triggered a debris flow that caused significant damages to buildings. The analysis aimed to better define the circumstances of this event, focusing on preconditioning, preparatory and triggering factors and their interaction with the destabilization process.The results provided interesting insights on the issue of destabilizing rock glaciers in the region. Permafrost distribution modeling demonstrated the large extents of the periglacial zone in the region as it can be found in debris slopes above 2300 - 2900 m.a.s.l. depending upon solar exposure and regional precipitation characteristics. Rock glacier destabilization was observed on 46 landforms, i.e. the 12% of the active rock glaciers. Destabilization was found to be more likely to occur in specific local topo-climatic conditions, consisting of north facing, steep and convex slopes at the lower margins of the permafrost zone. A large number of rock glaciers currently not showing destabilization was found to be located in these conditions and suggested to be susceptible to future destabilization. As demonstrated by the Lou rock glacier analysis, destabilization was found to be a relevant phenomena in the context of permafrost hazards. At this site, rock glacier destabilization was linked to a rapid frontal advance towards a torrential gully. This process seemed to have increased the site predisposition to frontal failure as a mild rainstorm was sufficient to trigger the event.Despite methodological uncertainties, results indicated that destabilization occurrence is widespread and it may rise the hazard level of a site connected to human infrastructures. Therefore, it is suggested that, where it has been modelled and where stakes may be at risk downslope, rock glacier destabilization deserves to be more carefully investigated. In this sense further efforts should focus towards a better understanding of the destabilization process by site monitoring as well as towards a comprehensive hazard assessment linked to this phenomenon.Le permafrost de montagne est menacé par le réchauffement atmosphérique, une évolution qui s’accompagne de l’augmentation des phénomènes tels que les chutes de pierres, la formation de thermokarsts et l’accélération des glaciers rocheux. La déstabilisation des glaciers rocheux, qui compromet l’intégrité structurelle de ces formes, semble liée au réchauffement atmosphérique, et a suscité un intérêt grandissant au cours des dernières années. Ce phénomène, qui peut être provoqué par le réchauffement du pergélisol ou des contraintes mécaniques externes, est caractérisé par une accélération anormale des glaciers rocheux affectés, et par l’apparition des signes géomorphologiques telles que des fissures et des crevasses à sa surface. Bien que ce processus peut être transitoire, il peut déterminer une phase de crise amenant le glacier rocheux à un effondrement.Cet étude se préfixe de fournir une première évaluation des phénomènes de déstabilisation de glacier rocheux à l’échelle des Alpes françaises. Dans un premier temps, l’empreinte spatiale du pergélisol a été évaluée afin de produire une carte de répartition du pergélisol régionale, un outil nécessaire pour estimer l’état du permafrost dans les glaciers rocheux. La deuxième étape a consisté à identifier les formes déstabilisées grâce à une observation ponctuelle des images aériennes afin d’identifier les caractéristiques typiquement observables sur les glaciers rocheux déstabilisés. Il est alors possible de comprendre les conditions topoclimatiques typiques dans lesquelles se produit ce phénomène et de repérer les formes susceptibles de subir ce processus. Enfin, les efforts ont été concentrés sur le glacier rocheux du Lou, déstabilisé, qui, du fait d’un détachement de couche active, a conduit à une lave torrentielle en Août 2015. L’analyse a visé à mieux définir les circonstances de cet événement, en mettant l’accent sur les facteurs de préconditionnement, de préparation et de déclenchement et sur leur interaction avec le processus de déstabilisation.Les résultats ont fourni des informations riches sur la zone périglaciaire de la région. La modélisation de la répartition du pergélisol a mis en évidence les étendues de la zone périglaciaire dans la région qu’on peut trouver sur les pentes de débris au-dessus de 2300 - 2500 m.a.s.l. en fonction de l’exposition solaire et des caractéristiques régionales des précipitations. L’observation des photographies aériennes a permis d’observer 46 formes en cours de déstabilisation, soit 12% des glaciers rocheux actifs des Alpes françaises. Il apparaît que la déstabilisation est plus susceptible de se produire dans certaines conditions topoclimatiques locales spécifiques, en particulier dans des pentes exposées au nord, raides et convexes situées aux marges inférieures de la zone de pergélisol. Un grand nombre de glaciers rocheux ne présentant actuellement aucune déstabilisation sont donc susceptibles d’être affectés par une déstabilisation future. L’analyse du glacier rocheux du Lou a révélé que la déstabilisation est liée à une avancée rapide du front vers un ravin torrentiel. Ce processus semble avoir accru la prédisposition des matériaux détritiques du front à être mobilisés par du ruissellement, des précipitations relativement modérées ayant suffi à déclencher l’événement.Malgré les incertitudes liées aux méthodes impliquées, les résultats suggèrent que les conditions favorables à la déstabilisation sont fréquentes, et que cette dernière peut augmenter le niveau de risque si le site est connecté à des infrastructures humaines. Des efforts supplémentaires doivent donc être entrepris, afin d’améliorer la compréhension de ces processus, notamment par la surveillance des sites ainsi que par une évaluation locale complète des cascades de processus liés à ce phénomène

Rock glacier destabilization in the French Alps : insights from regional and local scale assessments

Le permafrost de montagne est menacé par le réchauffement atmosphérique, une évolution qui s’accompagne de l’augmentation des phénomènes tels que les chutes de pierres, la formation de thermokarsts et l’accélération des glaciers rocheux. La déstabilisation des glaciers rocheux, qui compromet l’intégrité structurelle de ces formes, semble liée au réchauffement atmosphérique, et a suscité un intérêt grandissant au cours des dernières années. Ce phénomène, qui peut être provoqué par le réchauffement du pergélisol ou des contraintes mécaniques externes, est caractérisé par une accélération anormale des glaciers rocheux affectés, et par l’apparition des signes géomorphologiques telles que des fissures et des crevasses à sa surface. Bien que ce processus peut être transitoire, il peut déterminer une phase de crise amenant le glacier rocheux à un effondrement.Cet étude se préfixe de fournir une première évaluation des phénomènes de déstabilisation de glacier rocheux à l’échelle des Alpes françaises. Dans un premier temps, l’empreinte spatiale du pergélisol a été évaluée afin de produire une carte de répartition du pergélisol régionale, un outil nécessaire pour estimer l’état du permafrost dans les glaciers rocheux. La deuxième étape a consisté à identifier les formes déstabilisées grâce à une observation ponctuelle des images aériennes afin d’identifier les caractéristiques typiquement observables sur les glaciers rocheux déstabilisés. Il est alors possible de comprendre les conditions topoclimatiques typiques dans lesquelles se produit ce phénomène et de repérer les formes susceptibles de subir ce processus. Enfin, les efforts ont été concentrés sur le glacier rocheux du Lou, déstabilisé, qui, du fait d’un détachement de couche active, a conduit à une lave torrentielle en Août 2015. L’analyse a visé à mieux définir les circonstances de cet événement, en mettant l’accent sur les facteurs de préconditionnement, de préparation et de déclenchement et sur leur interaction avec le processus de déstabilisation.Les résultats ont fourni des informations riches sur la zone périglaciaire de la région. La modélisation de la répartition du pergélisol a mis en évidence les étendues de la zone périglaciaire dans la région qu’on peut trouver sur les pentes de débris au-dessus de 2300 - 2500 m.a.s.l. en fonction de l’exposition solaire et des caractéristiques régionales des précipitations. L’observation des photographies aériennes a permis d’observer 46 formes en cours de déstabilisation, soit 12% des glaciers rocheux actifs des Alpes françaises. Il apparaît que la déstabilisation est plus susceptible de se produire dans certaines conditions topoclimatiques locales spécifiques, en particulier dans des pentes exposées au nord, raides et convexes situées aux marges inférieures de la zone de pergélisol. Un grand nombre de glaciers rocheux ne présentant actuellement aucune déstabilisation sont donc susceptibles d’être affectés par une déstabilisation future. L’analyse du glacier rocheux du Lou a révélé que la déstabilisation est liée à une avancée rapide du front vers un ravin torrentiel. Ce processus semble avoir accru la prédisposition des matériaux détritiques du front à être mobilisés par du ruissellement, des précipitations relativement modérées ayant suffi à déclencher l’événement.Malgré les incertitudes liées aux méthodes impliquées, les résultats suggèrent que les conditions favorables à la déstabilisation sont fréquentes, et que cette dernière peut augmenter le niveau de risque si le site est connecté à des infrastructures humaines. Des efforts supplémentaires doivent donc être entrepris, afin d’améliorer la compréhension de ces processus, notamment par la surveillance des sites ainsi que par une évaluation locale complète des cascades de processus liés à ce phénomène.As occurring to several geosystems on our planet, mountain permafrost is threatened by climate change as prolonged warming may compromise the geotechnical properties of the frozen ground. As result, increasing occurrence of rockfall activity, thermokarst formation and rock glacier acceleration was observed in the past decades. Rock glacier destabilization, a process that compromises the structural integrity of these landforms, seems to be linked to atmospheric warming, gaining interest in the past years. The destabilization, which may be triggered by warming permafrost or mechanical stress, is characterized by an anomalous acceleration of the landform and the occurrence of specific features such as cracks and crevasses on its surface. Although the occurrence of these processes is mostly transitory, determining a textit{crisis} phase of the landform, in exceptional cases it may lead the rock glacier to structural collapse.This PhD thesis provided an assessment on the occurrence and related processes of rock glacier destabilization in the French Alps. At first, the spatial occurrence of debris permafrost was assessed in order to provide the permafrost distribution map of the French Alps, a tool that was necessary to evaluate permafrost conditions at rock glaciers sites. The second step consisted in an identification of destabilized rock glaciers in the region, which was done by multiple orthoimages interpretation aimed to identify features typically observable on destabilized rock glacier. Once identified the destabilized rock glaciers it was possible to analyse the typical topographical settings in which destabilization occurs and to to spot those landforms that are susceptible to experience this phenomenon. After these efforts at the regional scale, the focus was shifted towards local scale investigations at the Lou rock glacier, a partially destabilized landform that, due to frontal failure, in August 2015 triggered a debris flow that caused significant damages to buildings. The analysis aimed to better define the circumstances of this event, focusing on preconditioning, preparatory and triggering factors and their interaction with the destabilization process.The results provided interesting insights on the issue of destabilizing rock glaciers in the region. Permafrost distribution modeling demonstrated the large extents of the periglacial zone in the region as it can be found in debris slopes above 2300 - 2900 m.a.s.l. depending upon solar exposure and regional precipitation characteristics. Rock glacier destabilization was observed on 46 landforms, i.e. the 12% of the active rock glaciers. Destabilization was found to be more likely to occur in specific local topo-climatic conditions, consisting of north facing, steep and convex slopes at the lower margins of the permafrost zone. A large number of rock glaciers currently not showing destabilization was found to be located in these conditions and suggested to be susceptible to future destabilization. As demonstrated by the Lou rock glacier analysis, destabilization was found to be a relevant phenomena in the context of permafrost hazards. At this site, rock glacier destabilization was linked to a rapid frontal advance towards a torrential gully. This process seemed to have increased the site predisposition to frontal failure as a mild rainstorm was sufficient to trigger the event.Despite methodological uncertainties, results indicated that destabilization occurrence is widespread and it may rise the hazard level of a site connected to human infrastructures. Therefore, it is suggested that, where it has been modelled and where stakes may be at risk downslope, rock glacier destabilization deserves to be more carefully investigated. In this sense further efforts should focus towards a better understanding of the destabilization process by site monitoring as well as towards a comprehensive hazard assessment linked to this phenomenon

Dataset: Bedrock Permafrost in Sisimiut, West Greenland

This dataset contains the original data for the manuscirpt by Marcer et al, Modeling present and future rock wall permafrost distribution in the Sisimiut mountain area, West Greenland. The data are the basis to develop, calibrate and validate the numerical model describing rock wall permafrost in the Sisimiut area. The data consist of:Rock surface temperature data acquired during the hydrological years 2020-2022. The data are acquired by a network of 9 loggers installed in steep rock walls. Here, we provide the RST time series as .csv file, along with air temperature and incoming solar radiation evaluated using the TopoSCALE algorithm. The data are accompained by a .shp file describing loggers locations - EPSG 3413. Shp file can be open using any GIS software, e.g. Qgis.Field ERT acquired in October 2020. The data are acquired using Electrical Resistivity Tomography along a 100 m transect across a mid-elevation mountain ridge. Data are provided as .xls file and can be handled using Res2inv. The profile location is given as .shp file. Shp file can be open using any GIS software, e.g. Qgis.Laboratory data of rock samples acquired at the geophysical transect location. The data are provided as .xls file and describe the results of the petrophysical analysis linking samples' temperature and measured conductivity.Georasters providing the GIS data for visualization of the terrain in the study. All data is at 10 m resolution and ESPG 3413. We provide the DEM, derived from the Arctic DEM V3.0; the potential incoming solar radiation map. As modeling results, we provide georasters of mean rock surface temperatures during three climatic settings: present conditions (2002-2022), and at the end of the 21st century under the two scenarios RCP 2.6 and RCP 8.5. Georasters file can be open using any GIS software, e.g. Qgis.</p

Permafrost distribution in the French Alps : statistical modelling using rock glacier inventory

International audiencelong 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 issue

Reconstructing the last century evolution of the Dérochoir rock glacier using a multi-approach monitoring

PosterInternational audienc

A general theory of rock glacier creep based on in‐situ and remote sensing observations

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

Modeling the precision of structure-from-motion multi-view stereo digital elevation models from repeated close-range aerial surveys

International audienc