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The most common studies on colouring matter concern the question of the “chaîne opératoire” from procurement to use, dealing distinctively with archaeological remains and rock art. Only a few studies have been done on the link between excavated pieces and rock art, and even less have taken into account the correlation with geological origin. The “Grotte aux Points” presents the particularity of being decorated and archeological excavations reveal many pieces of coloured and colouring remains which are iron oxide-rich rocks brought to the site by Palaeolithic people. The red Palaeolithic paintings present a few palm-points, great signs and figurative drawings: a horse, a bison and ibexes.In 2015, coherent colouring matters, coloured limestone fragments and one µ-sample of painting were studied with complementary physico-chemical methods. To describe their morphology and composition, different instruments were used on macroscopic and microscopic scales: optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM), both coupled with dispersive X-ray energy probe (EDX). 10 objects were studied using proton induced X-ray emission (PIXE) in order to obtain quantitative chemical data on major and trace elements. Except for the TEM which gives information concerning the iron oxide crystal morphology and potential heat-treatment, non-invasive and non-destructive methods have been privileged to preserve the archaeological artefacts.About forty pieces of solid colouring agents were excavated in the Palaeolithic occupational levels. Most of the pieces have millimetric size (< 5 mm). At least three different raw ferruginous materials were discriminated including a ferruginous clayey rock containing green minerals dispersed in the matrix. We think that this mineral phase, which still needs to be clearly identified, is a good indicator of the geological origin of this kind of rock.In addition, three centimetric fragments of wall painting (from 3 cm to 20 cm) were discovered at the foot of the “large signs” panel. Finally, in 2012, a red palm-point with black charcoal pigment superposition was sampled from the “Niche aux Points”.The twenty-five archaeological remains (coloured limestone fragments and solid colouring agents), the 3 painted wall fragments and the micro-sample of painting were analysed in order to approach the chronology of the colouring matter used.These observations combined with chemical measurements actually permit (i) to characterize the signal of the environment on the different objects, (ii) to identify differences between macro-observations and geochemical fingerprints on the coherent matters (figures 10, 11). The raw material properties privileged by Palaeolithic people during supply were identified. First results are encouraging and enable to improve the methodology, particularly on a chemical point of view., Les fouilles conduites sous le porche de la Grotte aux Points ont mis au jour des matières colorantes solides et des résidus colorés sur des clastes calcaires au sein des dépôts archéologiques Paléolithique supérieur. De plus, dans la partie profonde de la cavité, des écailles de paroi présentant des aplats rouges ont été découvertes au pied de parois ornées. Cette association offre l'occasion de questionner les relations entre ces vestiges sous l'angle des choix de matières premières et des modalités de transformation, informations qui participent à la définition du cadre chronologique de fréquentation de la grotte, tant au niveau de son entrée que de la galerie ornée. Nous avons ainsi déterminé, en les comparant, les particularités pétrographiques, minéralogiques et géochimiques de ces matières. L'approche multi-scalaire adoptée repose sur la complémentarité des méthodes d'investigation ce qui permet de distinguer plusieurs géomatières colorantes au sein du corpus. En particulier, certains dépôts sur les clastes peuvent être attribués à des causes taphonomiques, alors qu'une forte parenté a pu être établie entre une géomatière colorante solide et les aplats rouges sur écaille de paroi.

Rockfalls and rock avalanches are active processes, including hazards for infrastructures and outdoor activities.Present rockfalls are well surveyed and documented in the Mont Blanc massif thanks to a network of observersset up in 2007, and composed of hut keepers, mountain guides, alpinists and infrastructure workers. Frequencyover the past 150 years of massif rockfall, studied by comparison of historical photographs, has strongly increasedduring the last 30 years, especially during very hot summer (2003 and 2015), likely due to permafrost degradationdriven by the climate change.In order to understand at a longer timescale the relationship between rockfall frequency and climate dynamicsin the Mont Blanc massif, we use Terrestrial Cosmogenic Nuclide (TCN) dating to obtain the exposure ages ofLateglacial and Holocene rockfall scars and old rockwall surfaces, and glacial and climate proxies to verify thehypothesis that rockfalls were more frequent in warm periods.55 samples have been collected at 9 sites of the Glacier du Géant basin, at elevation in the range 3300-3800 m a.s.l.These new exposure ages were completed by the 25 others TCN ages sampled during two previous campaigns andrecalculated using the newest input parameters. A total of 72 ages were obtained, between 0.04 ± 0.02 and 100.50± 8.50 ka.We found four age clusters. Two clusters are related to the Holocene Warm Period (∼ 6.1-7.4 ka) and RomanWarm Period (∼ 1.6-2.3 ka); a cluster of LIA-post-LIA ages is mainly composed by smaller rockfalls, consideredas the ‘normal’ erosion. A forth cluster have been recognized at ∼ 4.2-5.0 ka.Data suggest a relationship between the reflectance spectral data of the scar surfaces and exposure ages, mainlyin the E-SE-S aspects. Fresh rock surfaces of recent rockfall scars are light grey, whereas long-time exposedweathered rock surfaces range from light orange to dark red. This confirms the initial hypothesis: the redder a rocksurface, the older its age. Reflectance spectroscopy is used to quantify the granite surface colour and allow theestablishment of a robust relationship between scar exposure ages and colour of the rockwalls in the Mont Blancmassif.

Sedimentary archives are used to infer past climate and environment thanks to their physical and chemical properties. Sampling methods (millimetric or centimetric) and routine analysis are time and material consuming. The use of some specific spectroscopic methods and data analysis, allow to develop and perform some robust methods capable of (i) fast high resolution (ii) performed at low costs (iii) non-destructive and (iv) monitor concentration variations of major sediment compounds. X-ray fluorescence spectroscopy is one of these techniques, but it is able to detect just mineral geochemistrys. Whereas hyperspectral imaging (VNIR 400-1000 nm, SWIR 1000-2500 nm) allow, behind each voxel (a pixel with several wavelengths), to define spectral fingerprint of organic or mineral chemical compounds. This type of data can be analyzed by statistical techniques. Many (pseudo-) univariate coefficients are available for the quantification of some molecules (RABD845 for BPhe a, RABD660-670 for chlr-a and chlorins). But in this study we choose to applied multivariate methods that take into account all spectra variations. To achieve such study we can use technic that usually applied in classical spectroscopy or for satellite data that can be unsupervised or supervised. For unsupervised techniques, without any prior knowledge of the sample, exploratory algorithms are used to determine groups in the data. Then, these groups can be interpreted with the comparison to other analytical methods. It is possible to find pure signal that corresponds to one or several organic or mineral sedimentary compounds by (i) endmembers techniques, (ii) spectral unmixing, or (iii) clustering. For supervised techniques, we can use the knowledge of sample chemical and physical properties to create prediction models, then it is possible to observe variations of a specific property along the core. To develop qualitative and quantitative model for focused spectral properties we can applied classification and regression techniques. They allow to discriminate spectral domains or some wavelengths for some interest property. In the present study, Lake Le Bourget (Savoie, France) and Black Sea (Northwest margin) sediment cores are used. From this two different environmental systems we could create and test several prediction models. The high-resolution acquisition is done with two hyperspectral cameras: VNIR (400-1000 nm) and SWIR (1000-2500 nm) with spatial resolution of several dozen micrometers. Both sensors are well designed to create predictive models for either physical or chemical properties. In order to improve prediction models and make them more robust, we can pair these two cameras and add XRF core scanner data. For the black sea sediment, we use unsupervised techniques to determine groups and define interesting spatial areas to take samples for analytic analysis. Whereas for the Lake le Bourget sediment, several previous studies allow us to have many available data, thus supervised techniques are used to observe along core variations. For some properties, we could try to use models of the Lake Le Bourget in the Black Sea data, for example if we create a grain-size model, chemical elements ratio or organic compounds.

Glacial shrinkage and the gravitational processes associated with it, which are characteristic of global warming effects in high mountain environments, are affecting mountaineering routes more and more, including access routes to high altitude refuges. These changes have almost never been studied. Also, this research seeks to identify and explain the evolution of access trails to five refuges, located in the Mer de Glace basin (Mont Blanc massif), over more than a century. This glacier is the largest in France (L = 11.5 km, SA = 30 km²) is a major Alpine tourist attraction since 1741 and is the birthplace of mountaineering. This work is based on a three-step methodology: 1) collection and analysis of maps, climbing guidebooks and photographs, 2) semi-structured interviews and 3) analysis of high-resolution digital terrain models obtained through terrestrial laser scanning.While there was not a significant evolution during most of the 20th century, glacier thickness loss and the associated erosion of lateral moraines have resulted in numerous modifications made to the access trails since the 1990s. Despite these adaptations, the danger they pose continues to rise, and the necessity to equip them is ever more important (633 m. of ladders at present), which raises doubts about the future accessibility of such high mountain refuges., Le retrait glaciaire et les processus gravitaires associés, caractéristiques de l’évolution des milieux de haute montagne induite par le réchauffement climatique, affectent de plus en plus fortement les itinéraires d’alpinisme dont les sentiers d’accès aux refuges de haute altitude. Alors que ces changements n’ont quasiment fait l’objet d’aucune étude, cette recherche tente de caractériser et d’expliquer l’évolution sur un peu plus d’un siècle des accès aux cinq refuges situés autour de la Mer de Glace (massif du Mont Blanc), le plus grand glacier français (L = 11,5 km, S = 30 km2), haut lieu du tourisme alpin depuis 1741 et berceau de l’alpinisme. Ce travail repose sur une méthodologie en 3 étapes : 1) récolte et analyse de cartes, de topo-guides et de photographies, 2) conduite d’entretiens semi-directifs et 3) analyse de modèles numériques de terrain à haute résolution acquis par balayage laser terrestre. Si l’essentiel du xxe siècle ne présente pas d’évolution marquée, la perte d’épaisseur du glacier et la dégradation associée des moraines latérales ont donné lieu à de nombreuses modifications des itinéraires à partir des années 1990. Malgré ces adaptations, leur dangerosité s’accroit et la nécessité de les équiper est sans cesse plus importante (633 m d’échelles actuellement), remettant en question l’accessibilité future des refuges.

Poster; International audience; Snow bridges that form over the crevasses of the Alpine glaciers allow mountaineers and skiers to cross them easily but constitute an important danger in case of rupture. Between 2008 and 2014, 37 injured persons and 13 deaths related to falls into crevasse were recorded (i.e. an average of two deaths per year) on the glaciers of the French side of the Mont Blanc massif - out of the famous Vallée Blanche ski route, which however embodies an important part of the aid related to falls into crevasses. To understand the construction and evolution of these fragile structures, instrumentation was set up on the Glacier du Géant, at 3450 m a.s.l., near the Aiguille du Midi (3842 m a.s.l.), on the French side of the Mont Blanc massif, close to a crevasse whose bridge had recently collapsed over a length of 37 m. The maximum width of the crevasse in this area is 6 m. At the top of a 7-m-high pole - to prevent future snowfalls -, sensors have been installed in September 2016 to measure different snow and weather parameters: air temperature, wind speed and direction, snow height. An automatic camera surveys the crevasse and the snow bridge geometry. Several other sensors monitor the temperature of snow and air in the crevasse. In addition, an extensometer was installed into the crevasse to measure the evolution of its width. The results of the first 6 months of survey are presented, including the formation of the bridge in mid-November, during a period of snowfall associated with a strong wind. Although the instrumentation is well suited to the high mountain conditions, its maintenance is delicate due to the strong instability of the environment (glacier movements and extreme weather conditions, primarily) but the results of this work will bring new glaciological knowledges which should participate in a better safety on glaciers.

Rockfalls and rock avalanches are active processes in the Mont Blanc massif, with infrastructure and alpinists at risk. Thanks to a network of observers (hut keepers, mountain guides, alpinists) set up in 2007 present rockfalls are well surveyed and documented. Rockfall frequency over the past 150 years has been studied by comparison of historical photographs, showing that it strongly increased during the three last decades, especially during hot periods like the summer of 2003 and 2015, due to permafrost degradation driven by the climate change. In order to decipher the possible relationship between rockfall occurrence and the warmest periods of the Lateglacial and the Holocene, we start to study the morphodynamics of some selected high-elevated (>3000 m a.s.l.) rockwalls of the massif on a long timescale. Contrary to low altitude, deglaciated sites where study of large rockfall deposits allows to quantify frequency and magnitude of the process, rockfalls that detached from high-elevated rockwalls are no more noticeable as debris were absorbed and evacuated by the glaciers. Therefore, our study focuses on the rockfall scars. Their 10Be dating gives us the rock surface exposure age from present to far beyond the Last Glacial Maximum, interpreted as the rockfall ages. TCN dating of rockfalls has been carried out at the Aiguille du Midi in 2007 (Boehlert et al., 2008), and three other sites in the Mont Blanc massif in 2011 (Gallach et al., submitted). Here we present a new data set of rockfall dating carried out in 2015 that improves the 2007 and 2011 data. Furthermore, a relationship between the colour of the Mont Blanc granite and its exposure age has been shown: fresh rock surface is light grey (e.g. in recent rockfall scars) whereas weathered rock surface is in the range grey to orange/red: the redder a rock surface, the older its age. Here, reflectance spectroscopy is used to quantify the granite surface colour. Böhlert, R., Gruber, S., Egli, M., Maisch, M., Brandová, D., Haeberli, W., Ivy-Ochs, S., Christl, M., Kubik, P.W., Deline, P. (2008). Comparison of exposure ages and spectral propierties of rock surfaces in steep, high alpine rock walls of Aiguille du Midi, France. Proceedings of the 9th International Conference on Permafrost, 143-148. Gallach, X. et al. (submitted). Timing of rockfalls in the Mont Blanc massif (western Alps). Evidences from surface exposure dating with cosmogenic 10Be. Landslides.

Poster; On January 9, 2016 at 4:57, inhabitants of the municipality of Entremont-le-Vieux were awakened by the sound ofa large rock collapse detached from the Mont Granier (1933 m, Savoie, France), iconic mountain of the Chartreusemassif located between Chambery and Grenoble. Its north face, a 900-m-high natural geological cross section inUrgonian limestone, Hauterivian marls, Valanginian limestone and Berriasian marls, was affected in 1248 by ahuge collapse (500 million m3) that caused hundreds of fatalities.The SW pillar, shaped in the upper Urgonian limestone, climbed for the first time in 1964 and several times duringthe warm and dry autumn 2015, collapsed throughout its height (180 m) over a width of up to about 85 m witha volume certainly much higher than 100,000 m3. Blocks rolled down the western slope on about 700 m beforestopping in the forest. It is now notched over a hundred meter wide. No infrastructure was affected.The Granier has many predispositions to large instabilities. This is the western remaining part, largely fractured, ofa much eroded perched syncline whose inclination is oriented to the east. Fracturing and orientation of the stratacontributes to pre-cut limestone and marl. The Granier is also a major karstic area: the Granier plateau with itsmultilevel karst network (90 km of galleries explored) is a good model of polyphased karst network. The region isalso frequently affected by small earthquakes but seismicity does not appear to be a triggering factor. Conversely,the collapse has produced an M 2.2 earthquake. Besides rock fatigue related to what has just been mentioned anda vertical or overhanging topography, it is likely that heavy rains of days before the event and after a long periodof drought have unleashed the destabilization.The collapse is not comparable to the historical event of 1248, which had reshaped the entire northern side.However, its dimensions make the January 2016 event one of the major events of recent decades in the limestonewestern Alps. Events of this size are very rare in the currently available rockfall data series.There is now a significant residual risk of falling boulders while a large overhang just formed suggests probablecollapses in the short or medium term, with volumes exceeding 10,000 m3.

International audience; 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.; Dans le contexte du changement climatique actuel, les milieux de haute montagne sont soumis à de profonds bouleversements tels que la fonte des glaciers ou la dégradation du permafrost, à l’origine de mouvements de versant au sein des parois rocheuses comme des formations superficielles. Ces processus impliquent des risques directs de déstabilisation pour les infrastructures (refuges, remontées mécaniques, etc.). Dans un but de prévention de ces risques, un recensement des infrastructures de haute montagne dans les Alpes françaises a été réalisé à l’aide d’un Système d’Information Géographique constitué de plusieurs couches de données dont des cartes de la répartition potentielle du permafrost et de l’extension des glaciers depuis la fin du Petit Âge Glaciaire. 1769 infrastructures ont été identifiées dans des secteurs à permafrost probable et/ou éventuellement affectés par le retrait glaciaire. Un indice de risque a été construit afin d’identifier et classer les infrastructures potentiellement à risque. Il inclut une caractérisation de l’aléa et un diagnostic de la vulnérabilité. 10 % des infrastructures sont caractérisées par un risque fort de déstabilisation.