Paraglacial Rock Slope Adjustment Beneath a High Mountain Infrastructure—The Pilatte Hut Case Study (Écrins Mountain Range, France)

Landslides triggered by shrinking glaciers are an expected outcome of global climate change and they pose a significant threat to inhabitants and infrastructure in mountain valleys. In this study we document the rock slope movement that has affected the Pilatte hut (2,572 m a.s.l.) in the Écrins range (French alps) since the 1980s. We reconstructed the geometry of the unstable rock mass using Terrestrial Laser Scanning and quantified the unstable volume (~400,000 m3). Field observations and annual crack surveys have been used to identify the dynamics of past movements. These movements initiated in the late 1980s and have accelerated since 2000. The current trend seems to be toward a relative stabilization. Reconstruction of the glacier surface using past images taken since 1960 and “Structure from Motion” photogrammetry showed that the glacier probably applied stresses to the rock slope during its short-lived advance during the 1980s, followed by debuttressing caused by rapid surface lowering until the present day. The relationship between observed crack propagation and glacier surface change suggests that the rock slope instability is a paraglacial response to glacier surface changes, and highlights that such responses can occur within a decade of glacier change

Risk assessment of infrastructure destabilisation due to global warming in the high French Alps

Due to ongoing global warming, high alpine environments are affected by significant changes, such as glacial retreat and permafrost warming, which can trigger mass movements in rock slopes or superficial deposits. These processes generate a risk of direct destabilisation for high mountain infrastructures (huts, cable cars, etc.). To help prevent such risks, an inventory of all the high mountain infrastructures in the French Alps was carried out using a Geographic Information System. This combined several data layers, including the Alpine Permafrost Index Map and glacier inventories since the end of the Little Ice Age. 1,769 infrastructures were identified in areas probably characterised by permafrost and/or possibly affected by glacier shrinkage. An index of destabilisation risk was constructed to identify and rank infrastructures at risk. This theoretical risk index includes a characterisation of hazards and a diagnosis of vulnerability. 10 % of the infrastructures were characterised by a high risk of destabilisation

Paraglacial Rock Slope Adjustment Beneath a High Mountain Infrastructure—The Pilatte Hut Case Study (Écrins Mountain Range, France)

International audienceLandslides triggered by shrinking glaciers are an expected outcome of global climate change and they pose a significant threat to inhabitants and infrastructure in mountain valleys. In this study we document the rock slope movement that has affected the Pilatte hut (2,572 m a.s.l.) in the Écrins range (French alps) since the 1980s. We reconstructed the geometry of the unstable rock mass using Terrestrial Laser Scanning and quantified the unstable volume (~400,000 m3). Field observations and annual crack surveys have been used to identify the dynamics of past movements. These movements initiated in the late 1980s and have accelerated since 2000. The current trend seems to be toward a relative stabilization. Reconstruction of the glacier surface using past images taken since 1960 and “Structure from Motion” photogrammetry showed that the glacier probably applied stresses to the rock slope during its short-lived advance during the 1980s, followed by debuttressing caused by rapid surface lowering until the present day. The relationship between observed crack propagation and glacier surface change suggests that the rock slope instability is a paraglacial response to glacier surface changes, and highlights that such responses can occur within a decade of glacier change

Le permafrost de montagne face au changement climatique

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Induced polarization as a new tool to monitor the degradation of permafrost

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Le permafrost de montagne : enjeux, concepts et méthodes

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Analyse multi-méthodes de la déstabilisation d’un pylône de remontée mécanique implanté sur un glacier rocheux des Alpes françaises

International audienceIn 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

Temperature distribution in a permafrost-affected rock ridge from conductivity and induced polarization tomography

International audienceGeoelectric prospecting is a widely used method for detecting and studying permafrost. The electrical resistivity has been recently combined with induced polarization measurements both in the laboratory and in the field. The use of a recently developed petrophysical model allows the conversion of conductivity and normalized chargeability into temperature and water content. This methodology has been validated and independent modelling and data are used to assess the validity of the approach and discuss application to monitor parameters leading to landslides