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The panoramic cameras (PCs) on board Hexagon KH-9 (KH-9PC) satellite missions from 1971–1984 captured very high-resolution stereo imagery with up to 60 cm spatial resolution. This study explores the potential of this imagery for glacier mapping and change estimation. We assess KH-9PC imagery using data from the KH-9 mapping camera (KH-9MC), KH-4PC, and SPOT and Pléiades satellite imagery. The high resolution of KH-9PC leads to higher-quality DEMs, which better resolve the accumulation region of the glaciers in comparison to the KH-9MC. On stable terrain, KH-9PC DEMs achieve an elevation accuracy of

The panoramic cameras (PC) onboard Hexagon KH-9 satellite missions from 1971–1984 captured very-high resolution stereo imagery with up to 60 cm spatial resolution. This study explores the potential of this imagery for glacier mapping and change estimation. We assess KH-9PC imagery using data from KH-9 Mapping Camera (MC), KH-4PC as well as SPOT and Pleiades satellites. The high resolution of KH-9PC leads to higher quality DEMs, which better resolve the accumulation region of the glaciers in comparison to the KH-9MC. On stable terrain, KH-9PC DEMs achieve an elevation accuracy

This study is part of the ANR 14-CE03-0006 VIP Mont Blanc and the EU ALCOTRA AdaPT Mont Blanc project. The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years. Publisher PDF

Large collections of images have become readily available through modern digital catalogs, from sources as diverse as historical photographs, aerial surveys, or user-contributed pictures. Exploiting the quantitative information present in such wide-ranging collections can greatly benefit studies that follow the evolution of landscape features over decades, such as measuring areas of glaciers to study their shrinking under climate change. However, many available images were taken with low-quality lenses and unknown camera parameters. Useful quantitative data may still be extracted, but it becomes important to both account for imperfect optics, and estimate the uncertainty of the derived quantities. In this paper, we present a method to address both these goals, and apply it to the estimation of the area of a landscape feature traced as a polygon on the image of interest. The technique is based on a Bayesian formulation of the camera calibration problem. First, the probability density function (PDF) of the unknown camera parameters is determined for the image, based on matches between 2D (image) and 3D (world) points together with any available prior information. In a second step, the posterior distribution of the feature area of interest is derived from the PDF of camera parameters. In this step, we also model systematic errors arising in the polygon tracing process, as well as uncertainties in the digital elevation model. The resulting area PDF therefore accounts for most sources of uncertainty. We present validation experiments, and show that the model produces accurate and consistent results. We also demonstrate that in some cases, accounting for optical lens distortions is crucial for accurate area determination with consumer-grade lenses. The technique can be applied to many other types of quantitative features to be extracted from photographs when careful error estimation is important.

International audience; The intensity of the current climate change has strong consequences for high mountain tourism activities. Winter activities are currently the most studied (ski industry). However, the consequences of environmental changes are also strong in summer, as geomorphological processes are increased at high altitudes. The Mont Blanc Massif (Western Alps) is particularly favourable terrain for the development of research into these processes. Its emblematic high summits (28 of the 82 peaks > 4000 m in the Alps), its hundreds of glaciers, its particularly developed tourism with summer/winter equivalence, the practice of mountaineering, which is still very present, etc. all contribute to the interest of studying this geographical area. A lot of work has been carried out on glaciological and geomorphological issues. These studies, which concern the "physical" impact of climate change on the high mountains, are also supplemented by studies of their consequences on human societies. Amongst others, we can cite the question of the impacts on practices such as mountaineering or glacier tourism. Risk-related issues are also taken into account, with, for example, question related to the stability of infrastructures (huts, ski lifts) or the impact of glacial retreat on the formation of new, potentially dangerous lakes. Accordingly, the aims of this paper are to show the extent of the research developed on climate change in the Mont Blanc massif and how social and environmental sciences are interlinked to provide a holistic vision of the issues of this territory. As these experiments are not exactly interdisciplinary experiments, this presentation also aims to discuss the points that need to be developed in order to promote inter- and trans-disciplinary research.

The increasing rockfall frequency in high mountain rockwalls is generally associated with global warming via the permafrost warming but long series of high resolution data on rockfall are still necessary to better appreciate the evolution of their frequencies and volumes, and to better understand their triggering factors.Here we present an inventory of rockfalls surveyed by terrestrial laser scanning (LiDAR) since 2005 in the east face of the Tour Ronde (3792 m a.s.l.) in the Géant glacial basin (Mont Blanc massif).Between 2005 and 2018, the rockwall was scanned 12 times, giving 11 comparisons of 3D models [1]. These highlighted a very intense morphodynamics with 91 destabilizations with volumes between 1 and 15,578 m3 for a total volume of 31,610 m3 (mean erosion rate: 29,8 mm.yr-1). In the first year of measurement, the Bernezat spur was affected by a collapse of more than 700 m3 [2]. Then, it was affected by rockfalls not exceeding a few tens of m3. On the other hand, in the rest of the face, there is a very strong increase in rockfall activity, especially during the hot summer 2015 at the end of which (August 27) the most voluminous collapse of the whole period occurred.The modelled surface temperature distribution at the scale of the Mont Blanc massif [3] attests to the presence of permafrost throughout the rockslope, confirmed by temperature measurements carried out at 3, 30 and 55 cm deep in the rock at the base of the Bernezat spur between October 2006 and May 2009. In addition, the main collapses left massive ice, at the level of their scar, more or less mixed with rock debris. These different elements, associated with the fact that collapses occur essentially during and following the highest summer heat, point to the role of degradation of permafrost [4]. A collapse on December 4, 2018 at the level of the small spur located at the foot of the Bernezat and whose volume is estimated at 7000 m3 reinforces this hypothesis since the detachment surface was covered - except for its margins - by massive ice. This has been sampled and its dating will perhaps confirm the age of the ice present in the cracks of the permafrost-affected rockwalls of the Mont Blanc massif. In 2017, a collapse of 44,000 m3 in the north face of the Aiguille du Midi (3842 m a.s.l.) had exposed 4060 calBP ice. In the Tour Ronde case, ice/snow cover changes and glacial debutressing could also partly explain the rockfall activity. [1] Ravanel L. et al. (2010). Revue Française de Photogrammétrie et de Télédétection, 192 : 58-65.[2] Rabatel A. et al. (2008). Geophysical Research Letters, 35: L10502.[3] Magnin F. et al. (2015). Geomorphologie, 21: 145-162.[4] Ravanel L. et al. (2017). Science of the Total Environment, 609: 132-143.

Ice aprons are small but ubiquitous ice masses in high alpine ranges such as the Mont Blanc massif. Mainly present on its north faces above 3200 m a.s.l., they are a condition for practice of the so-called "traditional" mountaineering (now on the Intangible Cultural Heritage UNESCO list) and an indicator of the presence of permafrost in the bedrock. Most often thin (Very few studied, ice aprons however represent an important glacial inheritance. We suggest that ice aprons are made up of very old ice, likely the oldest surface one in the Alps. In the north face of the Mont Blanc du Tacul (4248 m a.s.l.) for example, following the disappearance of the upper layers due to the increased occurrence of summer heatwaves, the ice on the present surface formed c. 2700 ago years (cold phase of Göschener I), against probably 200-300 years for the ice at the front of the Mer de Glace, the largest glacier in the French Alps. We present the ice ages acquired from five ice aprons on rock walls of the Mont Blanc massif together with ice ages from two glacier tongues of the massif (Mer de Glace and Miage Glacier).

The study of the ice (cryostructures, cryostratigraphy, types and age) that partly fills the fractures in rockwall permafrost is necessary to better understand the increasing frequency/volume of rockfalls in the high alpine rockwalls. Typically inaccessible, this ice is visible only when a rockfall occurs, exposing previously hidden ice. Over the past two years, the two largest rockfalls of the decade in the Mont Blanc massif and a smaller one allowed to start the documentation of the rockwall permafrost ice. This poster aims to present the three cases. Up to now, dating has been carried out for only one of the three cases. How to date permafrost ice? Dating ice cores from alpine glaciers has shown the wide time span covered by these, from a few decades to several thousand years. Several dating methods are available to quantify the age. Counting the annual layers, which proved to be effective, is widely used in the study of mountain glaciers but cannot be used for the internal ice of the permafrost since it does not present these annual layers. Structure of the ice in the scar of the Trident of Tacul rockfall scar shows nevertheless a series of layers. We will therefore use radionuclide dating to obtain the absolute age of the ice. So far, only one age is available for interstitial ice from permafrost-affected rockwall: the ice sampled from a felt block that is part of the deposit of the 150'000 m 3 rockfall that occurred in Feb. 2014 at Piz Kesch (Swiss Alps

Unlike the superficial deposits in which the presence of permafrost is indicated by geomorphological evidences, its occurrence in the rock walls can only be suggested by the existence of perennial ice sheets or hanging glaciers. Everywhere else, only indirect (geophysics) or direct temperature measurements make it possible to verify its presence. In these rock walls, permafrost and its degradation due to global warming are at the origin of rock falls and rock avalanches with a devastating power. In order to know the state and the thermal evolution of the rock walls, to parameterize or validate the permafrost distribution models, or to survey the kinematics of the fractures in the bedrock, it is necessary to monitor these rock walls. This article presents the methods of instrumentation and the equipment used for more than 10 years in the Mont Blanc massif as well as the associated research questions., Contrairement aux formations superficielles au sein desquelles la présence de permafrost peut être attestée par certains indices géomorphologiques, son occurrence dans les parois rocheuses ne peut qu’être suggérée par l’existence de couvertures de glace pérennes ou de glaciers suspendus. Partout ailleurs, seules des mesures indirectes (géophysiques) ou directes de température permettent de vérifier sa présence. Dans ces parois, le permafrost et sa dégradation causée par le réchauffement climatique sont à l’origine d’écroulements et d’avalanches rocheuses aux effets dévastateurs. Pour connaître l’état et l’évolution thermique des parois, paramétrer ou valider les modèles de distribution du permafrost, ou suivre la cinématique des fractures qui découpent les massifs rocheux, il est donc nécessaire d’instrumenter les parois. Cet article présente les modalités d’instrumentation et les matériels utilisés depuis plus de 10 ans dans le massif du Mont Blanc ainsi que les questions de recherche qui leur sont associées., Ravanel Ludovic, Malet Emmanuel, Duvillard Pierre-Alain, Magnin Florence, Deline Philip, Guillet Grégoire, Troilo Fabrizio, Pogliotti Paolo, Morra di Cella Umberto, Beutel Jan, Gruber Stephan. Instrumentation thermique et cinématique des parois à permafrost du massif du Mont Blanc. In: Collection EDYTEM. Cahiers de géographie, numéro 19, 2017. Monitoring en milieux naturels. Retours d’expériences en terrains difficiles. pp. 27-38.