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Ice aprons are poorly studied and not well-defined thin ice bodies adhering to high altitude steep rock faces, but are present in most Alpine-type high mountain environments worldwide. This study aims to precisely define ice aprons based on a detailed analysis of their topographical characteristics in the Mont Blanc massif (western European Alps). For this, we accurately identified and precisely mapped 423 ice aprons using a combination of high-resolution optical satellite images from 2019. To better understand their relationship with other types of glaciers, especially the steep slope glaciers and other surface ice bodies, we built a detailed inventory at the scale of the massif that incorporates nine different types of perennial surface ice bodies. In addition, an analysis using different topographic factors helped us to better understand the preferred locations of the ice aprons. We show that they predominantly occur on west-oriented steep and topographically rugged rock slopes above the local Equilibrium Line Altitude (~3200 m a.s.l.), with concave profile curvatures around them that facilitate snow accumulation. They are also found in areas underlain by permafrost. The extensive inventory also helped us to identify different types of ice aprons based on their relationships with glaciers/ice bodies. The analysis shows that ice aprons existing at the headwall of large glaciers above a bergschrund are the most dominant ice apron type in the study area, with ~82% of the total. [ABSTRACT FROM AUTHOR]

Ice aprons (IAs) are part of the critical components of the Alpine cryosphere. As a result of the changing climate over the past few decades, deglaciation has resulted in a surface decrease of IAs, which has not yet been documented out of a few specific examples. In this study, we quantify the effects of climate change on IAs since the mid-20th century in the Mont-Blanc massif (western European Alps). We then evaluate the role of climate forcing parameters and the local topography in the behaviour of IAs. We precisely mapped the surface areas of 200 IAs using high-resolution aerial and satellite photographs from 1952, 2001, 2012 and 2019. From the latter inventory, the surface area of the present individual IAs ranges from 0.001 to 0.04 km². IAs have lost their surface area over the past 70 years, with an alarming increase since the early 2000s. The total area, from 7.93 km² in 1952, was reduced to 5.91 km² in 2001 (-25.5 %) before collapsing to 4.21 km² in 2019 (-47 % since 1952). We performed a regression analysis using temperature and precipitation proxies to understand better the effects of climate forcing parameters on IA surface area variations. We found a strong correlation between both proxies and the relative area loss of IAs, indicating the significant influence of the changing climate on the evolution of IAs. We also evaluated the role of the local topographic factors in the IAs area loss. At a regional scale, factors like direct solar radiation and elevation have an important influence on the behaviour of IAs, while others like curvature, slope, and size of the IAs seem to be rather important on a local scale. [ABSTRACT FROM AUTHOR]

This paper investigates the backscatter evolution and surface changes of ice aprons (IAs) by exploiting time series of X- and C-band SAR images from PAZ and Sentinel-1 satellites. IAs are extremely small ice bodies of irregular shape present on steep slopes and complex topographies in all the major high-Alpine environments of the world. Due to their small size and locations in complex topographies, they have been very poorly studied, and very limited information is known about their evolution and responses to climate change. SAR datasets can provide handy information about the seasonal behaviour of IAs since physical changes of IA surfaces modify the backscattering of RaDAR waves. The analysis of the temporal variations of the backscatter coefficient illustrates the effects of increasing temperatures on the surface of the IAs. All IAs considered in the analysis show a strong decrease in backscatter coefficient values in the summer months. The backscattering patterns are also supported by the annual evolution of the coefficient of variation, which is an appropriate indicator to evaluate the heterogeneity of the surface. Higher mean backscatter values in the X-band than in the C-band indicate surface scattering phenomena dominate the IAs. These features could provide key information for classifying IAs using SAR images in future research.

Ice aprons are poorly studied and not well-defined thin ice bodies adhering to high altitude steep rock faces, but are present in most Alpine-type high mountain environments worldwide. This study aims to precisely define ice aprons based on a detailed analysis of their topographical characteristics in the Mont Blanc massif (western European Alps). For this, we accurately identified and precisely mapped 423 ice aprons using a combination of high-resolution optical satellite images from 2019. To better understand their relationship with other types of glaciers, especially the steep slope glaciers and other surface ice bodies, we built a detailed inventory at the scale of the massif that incorporates nine different types of perennial surface ice bodies. In addition, an analysis using different topographic factors helped us to better understand the preferred locations of the ice aprons. We show that they predominantly occur on west-oriented steep and topographically rugged rock slopes above the local Equilibrium Line Altitude (~3200 m a.s.l.), with concave profile curvatures around them that facilitate snow accumulation. They are also found in areas underlain by permafrost. The extensive inventory also helped us to identify different types of ice aprons based on their relationships with glaciers/ice bodies. The analysis shows that ice aprons existing at the headwall of large glaciers above a bergschrund are the most dominant ice apron type in the study area, with ~82% of the total.

Periglacial rock walls are affected by an increase in rockfall activity attributed to permafrost degradation. While recent laboratory tests have asserted the role of permafrost in bedrock stability, linking experimental findings to field applications is hindered by the difficulty in assessing bedrock temperature at observed rockfall locations and time. In this study, we simulated bedrock temperature for 209 rockfalls inventoried in the Mont Blanc massif between 2007 and 2015 and 209,000 random events artificially created at observed rockfall locations. Real and random events are then compared in a statistical analysis to determine their significance. Permafrost conditions (or very close to 0°C) were consistently found for all events with failure depth > 6 m, and for some events affecting depths from 4 to 6 m. Shallower events were probably not related to permafrost processes. Surface temperatures were significantly high up to at least 2 months prior to failure, with the highest peaks in significance 1.5–2 months and 1–5 days before rockfalls. Similarly, temperatures at scar depths were significantly high, but steadily decreasing, 1 day to 3 weeks before failure. The study confirms that warm permafrost areas (> −2°C) are particularly prone to rockfalls, and that failures are a direct response to extraordinary high bedrock temperature in both frozen and unfrozen conditions. The results are promising for the development of a rockfall susceptibility index, but uncertainty analysis encourages the use of a greater rockfall sample and a different sample of random events. [ABSTRACT FROM AUTHOR]

In high alpine environments, glacial shrinkage and permafrost warming due to climate change have significant consequences on mountaineering routes. Few research projects have studied the relationship between climate change and mountaineering; this study attempts to characterize and explain the evolution over the past 40 years of the routes described in The Mont Blanc Massif: The 100 Finest Routes, Gaston Rébuffat’s emblematic guidebook, published in 1973.The main elements studied were the geomorphic and cryospheric changes at work and their impacts on the itinerary’s climbing parameters, determining the manner and possibility for an itinerary to be climbed. Thirty-one interviews, and comparison with other guidebooks, led to the identification of 25 geomorphic and cryospheric changes related to climate change that are affecting mountaineering itineraries. On average, an itinerary has been affected by nine changes. Among the 95 itineraries studied, 93 have been affected by the effects of climate change – 26 of them have been greatly affected; and three no longer exist. Moreover, periods during which these itineraries can be climbed in good conditions in summer have tended to become less predictable and periods of optimal conditions have shifted toward spring and fall, because the itineraries have become more dangerous and technically more challenging.

The Arp Nouva peat bog located in the upper Ferret Valley in the Mont Blanc massif was critically evaluated since published radiocarbon dates have led to controversial conclusions on the formation of this swamp. Radiocarbon dating of woody fragments from three pits of up to 1 m depth was used to discuss the question of whether the historically documented rock avalanche occurring in 1717 CE overran the peat bog or settled prior to its formation. For the deepest samples in the pits, calibrated radiocarbon ages between 1,652 and 1950 CE (95.4%; confidence level) were obtained, which fit very well into the time frame of the historical documented 1717 CE rock avalanche event. It can, therefore, be concluded that the Arp Nouva peat bog was formed by blockage of the Bella Combe torrent by the rock avalanche deposits. Furthermore, careful sample preparation with consequent separation of woody fragments from the bulk peat sample has shown that the problem of too old 14C ages can be circumvented. This work demonstrates that a combined geomorphological and geochronological approach is the most reliable way to reconstruct landscape evolution. The key to successful 14C dating is careful sample selection and the identification of the material that might not be ideal for chronological reconstructions.

The Grès Singuliers unit represents an anomalous occurrence of a siliciclastic-dominated sedimentary system typifying a restricted geographic area around the Mont Blanc massif. Deposited during Early Jurassic rifting, this unit was influenced by the tectonic processes responsible for its development. This contribution integrates and reconciles sedimentological, stratigraphic and tectonic data and discusses the tectono-sedimentary evolution of the Mont Blanc basement and its autochthonous sedimentary cover. Based on depositional facies, a petrographic and detrital zircon provenance analysis, we propose that the Grès Singuliers unit is mainly derived from erosion of the local basement and pre-rift sedimentary cover. Furthermore, recognition of Jurassic cataclasites and black gouges capping the Mont Blanc basement confirms the hypothesis that the Mont Blanc domain formed an extensional core complex. The source to sink relationship between the Mont Blanc detachment system and the Grès Singuliers unit, as well as timing and location within the Alpine rift system, allows us to interpret this unit as the syn-tectonic sedimentary response to crustal necking, responsible for the onset of localized severe crustal/lithospheric thinning in the European margin of the Alpine Tethys rift system. The main result of this study was to show that the exhumation and uplift of basement during crustal/lithospheric necking produced a new source area for clastic sedimentary systems. Therefore, the local occurrence of a siliciclastic unit similar to the Grès Singuliers along passive margins may be symptomatic of necking zones in other rift systems. [ABSTRACT FROM AUTHOR]

In the Mont Blanc massif (European Western Alps), rockfalls are one of the main natural hazards for alpinists and infrastructure. Rockfall activity after the Little Ice Age is well documented. An increase in frequency during the last three decades is related to permafrost degradation caused by rising air temperatures. In order to understand whether climate exerts a long‐term control on rockfall occurrence, a selection of paleo‐rockfall scars was dated in the Glacier du Géant basin [>3200 m above sea level (a.s.l.)] using terrestrial cosmogenic nuclides. Rockfall occurrence was compared to different climatic and glacial proxies. This study presents 55 new samples (including replicates) and 25 previously‐published ages from nine sampling sites. In total, 62 dated rockfall events display ages ranging from 0.03 ± 0.02 ka to 88.40 ± 7.60 ka. Holocene ages and their uncertainties were used to perform a Kernel density function into a continuous dataset displaying rockfall probability per 100 years. Results highlight four Holocene periods of enhanced rockfall occurrence: (i) c. 7–5.7 ka, related to the Holocene Warm Periods; (ii) c. 4.5–4 ka, related to the Sub‐boreal Warm Period; (iii) c. 2.3–1.6 ka, related to the Roman Warm Period; and (iv) c. 0.9–0.3 ka, related to the Medieval Warm Period and beginning of the Little Ice Age. Laser and photogrammetric three‐dimensional (3D) models of the rock walls were produced to reconstruct the detached volumes from the best‐preserved rockfall scars (≤0.91 ± 0.12 ka). A structural study was carried out at the scale of the Glacier du Géant basin using aerial photographs, and at the scale of four selected rock walls using the 3D models. Two main vertical and one horizontal fracture sets were identified. They correspond respectively to alpine shear zones and veins opened‐up during long‐term exhumation of the Mont Blanc massif. Our study confirms that climate primarily controls rockfall occurrence, and that structural settings, coincident at both the massif and the rock wall scales, control the rock‐wall shapes as well as the geometry and volume of the rockfall events. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Sidewall erosion because of rockfalls is one of the most efficient erosional processes in the highest parts of mountain ranges; it is therefore important to quantify sidewall erosion to understand the long‐term evolution of mountainous topography. In this study, we analyse how the 10Be concentration of supraglacial debris can be used to quantify sidewall erosion in a glaciated catchment. We first analyse, in a glaciated catchment, the cascade of processes that move a rock from a rockwall to a supraglacial location and propose a quantitative estimate of the number of rockfalls statistically mixed in a supraglacial sand sample. This model incorporates the size of the rockwall, a power law distribution of the size of the rockfalls and the mean glacial transport velocity. In the case of the Bossons glacier catchment (Mont Blanc massif), the 10Be concentrations obtained for supraglacial samples vary from 1.97 ± 0.24 to 23.82 ± 1.68 × 104 atoms g−1. Our analysis suggests that part of the 10Be concentration dispersion is related to an insufficient number of amalgamated rockfalls that does not erase the stochastic nature of the sidewall erosion. In the latter case, the concentration of several collected samples is averaged to increase the number of statistically amalgamated rockfalls. Variable and robust 10Be‐derived rockwall retreat rates are obtained for three distinct rockfall zones in the Bossons catchment and are 0.19 ± 0.08 mm year−1, 0.54 ± 0.1 mm year−1 and 1.08 ± 0.17 mm year−1. The mean 10Be retreat rate for the whole catchment (ca. 0.65 mm year−1) is close to the present‐day erosion rate derived from other methods. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract Hydrothermal monazite-(Ce) crystals from sub-horizontal and younger sub-vertical Alpine fissures located in the Mont Blanc and Aiguilles Rouges Massifs were dated by in-situ SIMS Th-U-Pb methods to identify major growth phases during deformation. Sub-horizontal clefts formed in a compressive regime that led to steep foliation and down-dip lineation in the Mont Blanc shear zones. Sub-vertical clefts formed during younger, strike-slip movements along boundaries on both sides of the Mont Blanc Massif and along Permocarboniferous deposits in the Aiguilles Rouges. All analyzed monazite-(Ce) crystals show signs of recrystallized, porous and complexly-zoned grains, indicative of dissolution-reprecipitation processes. Consequently, the crystals show three main growth phases at 11.5–10.5 Ma, 9 Ma and 8–7 Ma, interpreted as representing (re)crystallization during the onset of dextral strike-slip faulting and subsequent steps of activity along the dextral strike-slip fault system. Whereas monazite-(Ce) from the older horizontal clefts may record all three crystallization steps, monazite-(Ce) crystallization in vertical clefts from the Aiguilles Rouges Massif starts only at around 9 Ma. Comparison of monazite-(Ce) crystallization ages with thermochronometers indicates that the anastomizing network of vertical shear zones with down-dip lineation in the Mont Blanc Massif became overprinted at 11.5 Ma and only traces of an older monazite-(Ce) generation survived. Heat advection seems to have been locally sufficient to reset zircon-fission track ages. The vertical clefts of ca. 9 Ma age in the Aiguilles Rouges Massif indicate that strike-slip deformation occurred not only on the south-eastern but also the north-western boundary of the Mont Blanc Massif and may be linked to the increase in exhumation rate around that time. The identified deformation phases show that the external Massifs of the Western Alps (Aar, Mont Blanc, Aiguilles Rouges, Pelvoux) not only share a comparable tectonic position within the Alpine arc but also underwent a very similar tectonic evolution. Highlights • Hydrothermal monazite records deformation over ∼7 Ma in the Mont Blanc-Aiguilles Rouges area, Western Alps. • Two cleft generations with different orientations record a change from transpressional to pure strike-slip deformation in shear zones. • Ages record crystallization and dissolution-reprecipitation under low-temperature greenschist to sub-greenschist facies conditions. [ABSTRACT FROM AUTHOR]

In high alpine environments, glacial shrinkage and permafrost warming due to climate change have significant consequences on mountaineering routes. Few research projects have studied the relationship between climate change and mountaineering; this study attempts to characterize and explain the evolution over the past 40 years of the routes described in The Mont Blanc Massif: The 100 Finest Routes, Gaston Rébuffat's emblematic guidebook, published in 1973.The main elements studied were the geomorphic and cryospheric changes at work and their impacts on the itinerary's climbing parameters, determining the manner and possibility for an itinerary to be climbed. Thirty-one interviews, and comparison with other guidebooks, led to the identification of 25 geomorphic and cryospheric changes related to climate change that are affecting mountaineering itineraries. On average, an itinerary has been affected by nine changes. Among the 95 itineraries studied, 93 have been affected by the effects of climate change – 26 of them have been greatly affected; and three no longer exist. Moreover, periods during which these itineraries can be climbed in good conditions in summer have tended to become less predictable and periods of optimal conditions have shifted toward spring and fall, because the itineraries have become more dangerous and technically more challenging. [ABSTRACT FROM AUTHOR]

Rockfalls and rock avalanches are a recurrent process in high mountain areas like the Mont Blanc massif. These processes are surveyed due to the hazard they present for infrastructure and alpinists. While rockfalls and rock avalanches have been documented for the last 150 years, we know very little about their frequency since the Last Glacial Maximum (LGM). In order to improve our understanding, it is imperative to date them on a longer timescale. A pilot campaign using Terrestrial Cosmogenic Nuclide (TCN) dating of five samples was carried out in 2006 at the Aiguille du Midi (3842 m a.s.l.). In 2011, a larger scale study (20 samples) was carried out in five other test sites in the Mont Blanc massif. This paper presents the exposure ages of the 2011 TCN study as well as the updated exposure ages of the 2006 study using newer TCN dating parameters. Most of these exposure ages lie within the Holocene but three ages are Pleistocene (59.87 ± 6.10 ka for the oldest). A comparison of these ages with air temperature and glacier cover proxies explored the possible relationship between the most active rockfall periods and the warmest periods of the Holocene: two clusters of exposure ages have been detected, corresponding to the Middle Holocene (8.2-4.2 ka) and the Roman Warm Period (c. 2 ka) climate periods. Some recent rockfalls have also been dated (< 0.56 ka). [ABSTRACT FROM AUTHOR]

Providing quantitative constraints on late Pleistocene glacier fluctuations remains an important challenge for understanding glacier response to past and future climate changes. In most mountainous settings, paleo-glacier reconstructions are limited because they often lack precise temporal constraints. Different geochronological methods have been developed and applied to date specific geomorphological or sedimentological markers for paleo-glacier dynamics. Recently, OSL (Optically Stimulated Luminescence) surface exposure dating has been introduced and provides us with an opportunity to improve paleo-glacier reconstructions. This method is based on the sensitivity of the OSL signal from rock minerals to light, resulting in bleaching of the OSL signal within the upper first millimeters of the exposed rock surface, a process that depends on the exposure age, the rock type and the local setting (e.g. topographic shielding, bedrock orientation etc.). Here, we investigate the potential of OSL surface exposure along a vertical cross-section of polished bedrock surfaces with known post-LIA (Little Ice Age) exposure ages (from 3 to 137 years) along the Mer de Glace glacier (Mont Blanc massif, France). The infrared stimulated luminescence (IRSL) signals from rock slices exhibit increasingly deep bleaching profiles with elevation and thus exposure age, which is consistent with progressive glacier thinning since the LIA. Our results show that OSL surface exposure dating can be applied to periglacial environments, and is a promising tool for high-resolution reconstruction of ice extent fluctuations, both in space and time. [ABSTRACT FROM AUTHOR]

Rockfall is one of the main geomorphological processes that affects the evolution and stability of rock-walls. At high elevations, rockfall is largely climate-driven, very probably because of the warming of rock-wall permafrost. So with the ongoing global warming that drives the degradation of permafrost, the related hazards for people and infrastructure could continue to increase. The heatwave of summer 2015, which affected Western Europe from the end of June to August, had a serious impact on the stability of high-altitude rock-walls, including those in the Mont Blanc massif. A network of observers allowed us to survey the frequency and intensity of rock-wall morphodynamics in 2015, and to verify its relationship with permafrost. These observations were compared with those of the 2003 summer heatwave, identified and quantified by remote sensing. A comparison between the two years shows a fairly similar rockfall pattern in respect of total volumes and high frequencies (about 160 rockfalls > 100 m 3 ) but the total volume for 2003 is higher than the 2015 one (about 300,000 m 3 and 170,000 m 3 respectively). In both cases, rockfalls were numerous but with a low magnitude and occurred in permafrost-affected areas. This suggests a sudden and remarkable deepening of the active layer during these two summers, rather than a longer-term warming of the permafrost body. [ABSTRACT FROM AUTHOR]

On glaciers, the snow bridges that form above crevasses have hardly been considered by researchers up to now, despite their importance for high mountain activities (skiing, mountaineering) and the risks that their possible failure poses to practitioners. In order to improve our understanding of the formation and evolution of these fragile snow structures, we monitored during two years a succession of three crevasses located at 3450 m a.s.l. in the Mont-Blanc massif (France) using a set of sensors including an automatic camera, air temperature sensors, a wind vane-anemometer, and an extensometer. Geophysical profiles (ground penetrating RaDAR) were also carried out to clarify the glacial context. Despite particularly extreme monitoring conditions, at the level of a bump formed by the bedrock under an ice thickness of c. 25 m, we have shown that a wind event parallel to the crevasse favours its filling by snow while a strong wind making a significant angle with the crevasse under largely negative temperatures can rapidly create a snow bridge by cornice accretion that grows by extending leeward. High temperatures are responsible for most of the natural failures of SBs. These elements are already used for risk mitigation. • Two years of monitoring of crevasses located at 3450 m a.s.l. in the Alps • Crevasses are formed at the level of a bedrock bump with an ice thickness of 25 m • A wind event parallel to the crevasse favours its filling by snow • A strong perpendicular wind can rapidly create a snow bridge by cornice accretion • High temperatures are responsible for most of the natural failures of SBs [ABSTRACT FROM AUTHOR]

Rockfalls are dominant in the rock slopes and rock ridge morphodynamics in high mountain areas and endanger people who pass along or stay there, as well as infrastructure that host them (cable cars, refuges). Risks are probably greater now because of fast permafrost degradation and regression of surface ice, two consequences of the atmospheric warming of the last decades. These two commonly associated factors are involved in the instability of rock slopes by modifying the mechanical behaviour of often ice-filled rock fractures and the mechanical constraints in the rock masses. This paper examines over 15 years the instability of the lower Arête des Cosmiques on the French side of the Mont Blanc massif. Its vulnerability is due to the presence of a high-capacity refuge on its top (3613 m a.s.l.). In 1998, a part of the refuge was left without support when a collapse of 600 m3 occurred immediately below it. Since this date, reinforcement work has been carried out in this area, but the whole ridge has been affected by around 15 relatively shallow rockfalls. Through a multidisciplinary approach, this article assesses the role of the cryospheric factors in the triggering of these rockfalls. [ABSTRACT FROM AUTHOR]

ABSTRACT One of the most glacierized areas in the European Alps, the Mont Blanc massif, illustrates how fast changes affect the cryosphere and the related morphodynamics in high mountain environments, especially since the termination of the Little Ice Age. Contrasts between the north-west side, gentle and heavily glaciated, and the south-east side, steep and rocky, and between local faces with varying slope angle and aspect highlight the suitability of the study site for scientific investigations. Glacier shrinkage is pronounced at low elevation but weaker than in other Alpine massifs, and supraglacial debris covers have developed over most of the glaciers, often starting in the nineteenth century. Lowering of glacier surface also affects areas of the accumulation zone. While modern glaciology has been carried out in the massif for several decades, study of the permafrost has been under development for only a few years, especially in the rock walls. Many hazards are related to glacier dynamics. Outburst flood from englacial pockets, ice avalanche from warm-based and cold-based glaciers, and rock slope failure due to debuttressing are generally increasing with the current decrease or even the vanishing of glaciers. Permafrost degradation is likely involved in rockfall and rock avalanche, contributing to the chains of processes resulting from the high relief of the massif. The resulting hazards could increasingly endanger population and activities of the valleys surrounding the Mont Blanc massif. [ABSTRACT FROM AUTHOR]

Rockfalls fundamentally affect the morphodynamics of high mountain rockwalls, and represent a great danger for both people and infrastructures, but still are poorly known. By comparing old, recent and new photographs, in addition to geomorphological field data, we propose an inventory of the rockfalls that occurred since the end of the ‘Little Ice Age’ on the north side of the Aiguilles de Chamonix (Mont Blanc massif), ranging in volume from 500 to 65 000 m 3. These 42 rockfalls occurred after 1947, of which > 70% during the last two decades, with a maximal frequency during the warm summers, especially in 2003. Average elevation of scars (3130 m a.s.l.) close to the lower modelled permafrost limit, and the topography (e.g. spurs) of the affected rock faces enhancing lateral heat fluxes, suggest that a climatically driven permafrost degradation has triggered many of the recent rockfalls in high-Alpine steep rockwalls. [ABSTRACT FROM AUTHOR]

Due to a lack of systematic observations, the intensity and volume of rock falls and rock avalanches in high mountain areas are still poorly known. Nevertheless, these phenomena could have burly consequences. To document present rock falls, a network of observers (guides, mountaineers, and hut wardens) was initiated in the Mont Blanc Massif in 2005 and became fully operational in 2007. This article presents data on the 66 rock falls (100 m ≤ V ≤ 50,000 m) documented in 2007 ( n = 41) and 2008 ( n = 25). Most of the starting zones are located in warm permafrost areas, which are most sensitive to warming, and only four rock falls are clearly out of permafrost area. Different elements support permafrost degradation as one of the main triggering factors of present rock falls in high mountain areas. [ABSTRACT FROM AUTHOR]

Abstract: Deposits in upper Val Ferret (Mont Blanc Massif, Italy) have been attributed to glacier advances and to a rock avalanche of 12 September AD 1717. We review evidence for the timing and mode of emplacement of the deposit, and present a new geomorphic interpretation and relative and absolute dating to show that the AD 1717 deposit is less extensive than previously thought. The landslide was deflected along one side of the valley floor, preserving older slope and morainic sediments along the other side. An earlier rock avalanche onto the Triolet Glacier occurred before AD 1000. The deposits of these landslides partly cover older moraine several kilometres downstream from the present glacier front, and have affected the glacier regimen and construction of its moraines. This study highlights the geomorphic impact of rock avalanches in glacierized high mountains. [Copyright &y& Elsevier]

The contribution of climate and tectonics to the Neogene exhumation history of the European Alps is studied in the Mont Blanc (MB) massif using low-temperature thermochronology. Apatite fission track and (U-Th-[Sm])/He data suggest that the MB massif was exhumed episodically: Rapid exhumation (2.5 ± 0.5 km/Ma) before 6 Ma is followed by an episode of slow exhumation and a period of accelerated exhumation (>1 km/Ma) after ∼3 Ma. Comparing the exhumation rates of the MB massif with reported exhumation rates of all other external crystalline massifs (ECM) shows that the MB massif is the only ECM that experienced rapid exhumation before 6 Ma, which is possibly related to NW and minor SE directed thrusting of the MB massif. The data demonstrate that the Messinian base level drop (∼5.5 Ma) and the increase in atmospheric moisture caused by an intensification of the Atlantic Golf Stream (4.6 Ma) did not affect the exhumation of the external Alps. All ECM, except the Gotthard massif, show an increase in exhumation rates at ∼3 Ma. We interpret this as the result of normal faulting along orogen-parallel faults and beginning Alpine glaciation. The relative impact of these processes on the exhumation of the ECM can vary spatially and temporally, mainly depending on differences in geology and geomorphology. In the case of the MB massif we propose that the acceleration in exhumation rates at ∼3 Ma is caused by rapid valley incision related to glaciation, and that the recent relief of the MB massif is thus a young feature. [ABSTRACT FROM AUTHOR]

Abstract: High resolution in situ surface temperature measurements of supraglacial debris cover on Miage Glacier, Mont Blanc Massif, Italy, are compared to ASTER-derived surface temperature data (TIR band, acquisition time 10:40 UTC+1:00 on 01–08–2005, in the frame of GLIMS project). Spatial patterns of surface temperature and supraglacial debris cover distribution revealed in the two datasets are described. The ground- and remotely sensed temperatures correlate strongly over continuously debris-covered areas (r =0.8), while on partially debris-covered ice (i.e. crevassed areas and ice cliffs) the correlation is weaker (r =0.69 over the whole glacier tongue). A map representing the spatial distribution and thickness of the debris cover is derived from the ASTER surface temperature data using debris-surface temperature–thickness relationships (r =0.8), calculated in 100 m elevation bands. Over <1 day, surface temperature is influenced by surface meteorological conditions, shading, roughness and elevation; over period of >1 week, debris thickness is the primary control. Both ground and remotely sensed data predict well the thick debris cover at the terminus and its upstream decrease, and broad cross- and along-glacier patterns of debris thickness are revealed in the ASTER data, e.g. moraines, crevassed areas. Finer details in the debris thickness distribution are not revealed in the ASTER data, due mainly to the coarse 90 m resolution of the thermal-band imagery. [Copyright &y& Elsevier]

Abstract: A quantitative analysis was performed with the aim of identifying changes in the volume and thickness of the Brenva Glacier tongue (Mont Blanc Massif, Italy) in the second half of the 20th century. This analysis was based on the comparison of digital elevation models (DEMs) derived from historical records, specifically maps (1959, 1971, 1983, 2003) and photogrammetric surveys (1991, 1997). The DEMs were generated by means of a digital photogrammetric workstation, with semi-automatic and automatic procedures. Problems relating to the identification of the control points in the photos had to be resolved in order to define the external orientation. An unconventional photogrammetric methodology, based on the identification of homologous points in zones considered outside of the glacier area, was adopted to insert the surveys into a single reference system. Furthermore, along with the photogrammetric data, DEMs derived from digitized historical maps were generated and compared to define changes in the geometry of the glacier tongue. The results indicated a positive long-term glacier tongue balance. In fact, between 1959 and 2003, there was an increase of 22.6×106 m3, equal to an average thickness of ca.+34 m (+0.7 m a−1 w.e.). Validation of the data obtained from comparison of the DEMs and the reliability of the results were discussed as well. [Copyright &y& Elsevier]

Because of insulation by supraglacial debris, the dynamics of debris-covered glaciers differ from those of 'clean' glaciers. Thus, changes in debris cover have to be taken into account when interpreting glacier fluctuations in terms of climate forcing. Three large glaciers in the Mont Blanc massif were investigated for the period since the termination of the 'Little Ice Age' (LIA) using historical and scientific documents of the eighteenth and nineteenth centuries. Although debris cover was limited to its frontal area until the 1840s, Miage Glacier exhibited a continuous debris cover in the first decades after the LIA, increasing to its present extent by the 1930s. On the Mer de Glace, a partial debris cover formed by coalescence of two of the four medial moraines at the close of the LIA; until 1890, these moraines have formed the present Veine noire ('Black vein'). In contrast, Brenva Glacier had a continuous debris cover at the end of the eighteenth century, possibly following a rock avalanche in 1767. For glaciers like Mer de Glace and Miage Glacier, the close of the LIA represents a threshold marked by a rapid change in state from 'clean' to debris-covered; for others, long-term debris accumulation or frequent rock avalanching (e.g., Brenva Glacier) mask the climate control of a slow post-LIA expansion of debris cover. [ABSTRACT FROM AUTHOR]