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The Glaciated Slopes of the High Alpine Mountains: Holocene Evolution and Impacts of the Current Climate Crisis

Ludovic Ravanel, Melaine Le Roy, Florence Magnin et Marta Chiarle
Cet article est une traduction de :
Les versants englacés de la haute montagne alpine : Évolution holocène et impacts de la crise climatique actuelle [fr]

Texte intégral

The coordinators of this special issue would like to extend their warmest thanks to the editors of the Journal of Alpine Research|Revue de géographie alpine, Olivier Vallade and Sébastien Hardy, as well as the special editor of this issue, Prof. Monique Fort, for all the work they put into compiling the ten previously unpublished contributions on glaciers and permafrost in the Alps. The coordinators would also like to extend their warmest thanks to the twenty or so reviewers who worked to improve these contributions and to Maxime Frezat for the layout.

Hot Flush on the Alpine Mountains

1After the wake-up calls of the summers of 2003 and 2015, along with their significant media impact, the succession of the summers of 2022 and 2023 represents a third stage and a clear acceleration in the warming and morphodynamics of the high Alpine mountains. In Chamonix, at the foot of Mont Blanc, these four years respectively rank as the third, fourth, first, and second-hottest summer seasons since measurements began in 1934 (MétéoFrance data). The morphodynamics of high mountain environments, already influenced by steep terrain and lengthy slopes, have experienced an unprecedented acceleration due to glacier retreat and permafrost warming (Sommer et al., 2020; Magnin et al., 2023). The most noticeable signs of these changes are the highest glacier losses, such as the Mer de Glace glacier’s thickness decreasing by more than 16 m at the Montenvers tourist site in 2022 (data from L. Moreau), and over 10% of the volume of Swiss glaciers being lost in only two years (GLAMOS data). Additionally, the frequency of rockfalls affecting the Mont Blanc massif has reached unprecedented levels in recent decades, with nearly 300 events in 2022 (data from L. Ravanel). In the Italian Alps, the number of rock slope movements at high elevations has doubled in 2022 compared to the period of 2000–2021 (Geoclimalp data). These disruptions are now even observable at the highest altitudes, including areas above 4,000 m a.s.l., which were relatively untouched until now. The altitude of the roof of Western Europe, measured in September 2023 at 4805.59 m a.s.l., has not been this low since the first topographic survey conducted by Captain Jean-Joseph Mieulet in 1863. This suggests that we may already be witnessing the consequences of rising temperatures, which are becoming increasingly prominent at these altitudes. For instance, on June 18, 2022, a temperature of 10.4 °C was recorded at Col Major, near the summit of Mont Blanc (ARPA VdA data), and there was a recent record sequence of four consecutive days with a 0 °C isotherm reaching and exceeding 5000 m a.s.l. at the beginning of September 2023. The rapid climate change occurring in the Alps is making the future of glaciers and permafrost areas increasingly central concerns for environmental, heritage, economic, and safety reasons (IPCC, 2019). These components of the cryosphere could virtually disappear from the Alps by the end of the century (Magnin et al., 2017; Rounce et al., 2023), with significant consequences in terms of resources and risks.

A Career Focused on High Mountains and Towards Others

2After a decade in the industry, getting an Agrégation degree in Geography in 1997, completing a PhD thesis titled “Geomorphological study of interactions between rockfalls and glaciers in the high Alpine mountains: the south-eastern side of the Mont Blanc massif (Aosta Valley, Italy)”, which he defended in 2002, and dedicating the last 18 years to his role as Senior Lecturer at the University Savoie Mont Blanc, Philip Deline is retiring coinciding with the publication of this special issue of the Journal of Alpine Research. His primary research topics have focused on glaciers and rockwall permafrost. Since the publication of his first article in this journal in 1998, titled “The morphodynamic tiering of high Alpine mountains: the example of Val Veny (Aosta Valley, Italy)”, he has been committed to investigating the post-glacial morphodynamics of glaciated high Alpine mountains, with a particular emphasis on the Italian side of the Mont Blanc massif. Over the past 25 years, five main lines of research have been developed.

3The first area of focus concerns fluctuations of Alpine glaciers since the Lateglacial, serving as a significant source of paleo-environmental insights in mountain regions. These fluctuations are reconstructed through a combination of geomorphological approaches involving moraine complexes and deposits, which are further dated using various complementary methods, including dendrochronology, cosmogenic dating, and radiocarbon dating (Deline, 1999; Deline and Orombelli, 2005). With M. Le Roy’s PhD thesis, a multi-proxy approach has allowed for the development of a Holocene chronology of glacial variations in the French Alps (Le Roy et al., 2015; 2017), similar to the approaches previously established in the Swiss and Austrian Alps (Nicolussi and Patzelt, 2001; Holzhauser et al., 2005). Furthermore, the first comprehensive inventory of glaciers in the French Alps since the end of the Little Ice Age (LIA) was conducted during M. Gardent’s PhD thesis as part of the Franco-Italian GlaRiskAlp project (Gardent, 2014).

4The second area of research is focused on the recent and current dynamics of debris-covered glaciers, which are glaciers partially covered with rock debris. Philip has made this one of his specialties, investigating the unique nature of fluctuations in their fronts, the formation and growth of their enlarged moraine complexes, the processes by which they accumulate debris, and the changes in their surface debris cover. Field and diachronic geomorphological studies, based on aerial photographs of the debris cover of several debris-covered glaciers, including Miage Glacier and Mer de Glace (Deline, 2005), as well as the small Estelette Glacier (Kirkbride and Deline, 2013; Deline and Kirkbride, 2017), have validated a model that connects the expansion of the debris cover with the glacier mass balance, alternating between phases dominated by transport (positive mass balance) and ablation (negative mass balance).

5In tandem with the aim of gaining a deeper understanding of the formation of debris covers, the lecturer-researcher has embarked on a third line of research concerning significant historical and contemporary rockfalls and their interactions with glaciers (Deline, 2009; Deline et al., 2022). The presence of glaciers alters the conditions under which rockfalls propagate and settle, and conversely, these deposits influence glacier dynamics. By dating the deposits of major rockfalls using the in situ produced cosmogenic radionuclides, significant events such as the 1717 rock avalanche in the Triolet glacier basin (Deline and Kirkbride, 2009; Akçar et al., 2012; Hajdas et al., 2021), or an event dating back to the Early Middle Ages at the Frébouge Glacier (Dieleman et al., 2023), have been reconstructed. The chronology of significant Holocene rockfalls on the Brenva Glacier is currently the most extensive in the Alps, with seven major rockfalls (>1 × 106 m3) occurring over the past 3,500 years (Deline, 2001; Deline et al., 2015). Recent major events in the Alps, some of which have been deadly, such as the one at Piz Cengalo (Grisons, Switzerland; Walter et al., 2020), highlight the significance of this research for risk assessment.

6A fourth line of research, built upon the previous one, investigates the frequency and volume of rockfalls occurring in high-altitude rock walls. With L. Ravanel’s PhD thesis, recent collapses (since the end of the LIA through the comparison of photographs) and ongoing events (monitored by a network of observers) have been studied in the Mont Blanc massif (Ravanel and Deline, 2008; 2011; 2013). Their temporal and spatial distribution highlights how, particularly during warmer periods, these rockfalls affect steep rock slopes characterised by temperate permafrost (close to 0 °C). These data were complemented by a diachronic analysis involving high-resolution 3D models obtained annually since 2005 through terrestrial laser scanning of approximately a dozen selected rock faces in the massif (Guerin et al., 2020). X. Gallach’s PhD thesis has further extended the temporal scope by reconstructing the historical frequency of rockfalls affecting the rock walls of the Mont Blanc massif over several tens of thousands of years, using the in situ produced cosmogenic radionuclides to date numerous rockfall scars (Gallach et al., 2018; 2020). Once again, the warm periods of the Holocene were conducive to rock slope movements.

7The fifth area of research, which perfectly complements the previous one, centres on the study of permafrost in high altitude rock walls. Philip was the first French researcher to investigate rockwall permafrost and the impacts of its warming in the context of climate change, catalysing a robust initiative that has led to the European PERMAdataROC and PermaNET projects. This line of research relies significantly on the comprehensive monitoring system developed since 2005 at the summit of Aiguille du Midi (3842 m a.s.l.). It primarily focuses on characterising the thermal regime within the rock, featuring numerous international collaborations (Magnin et al., 2015a). F. Magnin’s PhD thesis investigates the variations in rockwall temperature based on aspect and time, as well as the influence of snow on the thermal regime. A statistical model for the surface temperature of the rock faces in the Mont Blanc massif has been developed (Magnin et al., 2015b), which has been validated by geophysical measurements on different rock walls of the massif (Magnin et al., 2015c). These progresses in characterising steep permafrost has enabled the modelling of its evolution from the end of the LIA (around 1855) to the year 2100 (Magnin et al., 2017).

8Beyond the Western Alps, Philip’s passion for high mountains, his scientific rigor, and his remarkable power of observation led him to produce paleo-glacial reconstructions in the southern Russian Altai (Deline et al., 2020, 2023) through collaborations with archaeologists. He has also engaged in research in the northern Kerguelen Archipelago for paleo-climatological purposes.

9This thematic issue serves as a tribute to Philip Deline’s illustrious academic career, his leadership in numerous research projects that have led to internationally recognised work, his extensive contributions to scientific literature, and his diverse teaching activities, all highly valued by his students. It also acknowledges the responsibilities he has undertaken with deep humanistic principles. This tribute encompasses a collection of multidisciplinary contributions related to the core research question that continues to drive him: the impact of past and present climate change on the cryosphere of mountain slopes. The research on paleoenvironments and the current dynamics of high mountain regions presented in this issue will contribute to preparing responses that society anticipates regarding glacial and periglacial hazards, the state of the Alpine cryosphere, and the vanishing of glaciers.

Articles

10The original contributions in this special issue are grouped under three main topics.

11The evolution of glaciers during the late Holocene is here presented through the lens of three complementary methods: dating LIA moraines via dendrochronology (Le Roy et al.), utilising art as a source of geomorphological information by studying the abundant pictorial representations that defined the Alps in the 19th century (Nussbaumer and Zumbühl; Kirkbride et al.), and employing spatial remote sensing to accurately characterise recent changes in the cryosphere (Rabatel et al.).

12Several methods are employed to date glacier variations throughout the Holocene. Dendrochronology stands out as the most effective due to its annual, and even seasonal, precision and its applicability, covering a significant portion of the current interglacial period. Le Roy et al. contribute by presenting dendrochronological dating results that establish the maximum extent of two glaciers in the Arolla region (Valais, Switzerland) during the LIA. Based on the obtained dates, these two glaciers reached their maximum extension in the mid-1810s, specifically between 1813 and 1816, preceding the cooling resulting from the eruption of Mount Tambora. When dendrochronology is not applicable, historical sources can be utilised, and, in the context of the Alps, an invaluable resource has been harnessed. This resource consists of numerous paintings depicting glacial landscapes, whose accuracy was recognised from the late 18th century onwards. The article by Nussbaumer and Zumbühl provides an overview of the works by the captivating painter Jean-Antoine Linck from the period 1790–1820, focusing on quantifying the variations of two glaciers in the Chamonix valley, the Mer de Glace and the Bossons Glacier, during the interval of a slight retreat within the LIA centred on 1800, as witnessed by Linck. Unlike artists such as Jean-Antoine Linck and Samuel Birmann, known for their faithful, nearly photographic representation of landscapes, some contemporary artists depicted the same subjects with a different sensibility. The renowned English painter J.M.W. Turner visited the Alps multiple times in the early 19th century, emphasising his feelings about the landscape and the geomorphological forces at work, processes that deeply fascinated him, including avalanches, rockfalls, and serac falls. Turner aimed to convey the meaning the landscape held for him rather than just its appearance. The article by Kirkbride et al. offers a fresh interpretation of two paintings from an 1836 journey to the Italian side of the Mont Blanc massif. One painting, initially believed to depict the Brenva Glacier, was reidentified as representing Miage glacier and Mont Blanc (Val Veny). The second painting is, for the first time, interpreted as a later, amalgamated representation of the Triolet disaster of 1717, an event involving a rock avalanche that led to ice disruption and the tragic death of seven shepherds in the Italian Val Ferret, which the authors believe left an indelible mark on the collective memory and inspired Turner to re-imagine the event. The Italian side of the Mont Blanc massif (Val Veny) is also the subject of the article by Rabatel et al., which details the contribution of satellite observations in quantifying changes in glaciers since 2000. Advances in this field have enabled the quantification of surface and volume losses, along with glacier flow rates. A notable result of this study, in the context of glacier decline, is the identification of a highly dynamic zone in the Brenva accumulation basin, characterised by increasing velocities. The authors propose several hypotheses to elucidate this counter-intuitive finding. Overall, the authors estimate that the loss of glacial volume could reach 40% by 2050 across the entire region.

13The thermal evolution of mountain permafrost since the end of the 20th century is examined through two distinct paths. First, instrumented rock glaciers, featuring time series data that provide a unique insight into the mechanisms of permafrost degradation in low-slope blocky deposits, are explored (Haeberli et al.). Second, the changes in temperatures at instrumented sites on high-altitude rock walls in the Italian (Pogliotti et al.) and French Alps (Magnin et al.) are investigated. In the latter, the study presents key findings from the inventory of collapses that have impacted the rock walls of the Mont Blanc massif over the past 15 years. Lastly, an extension of this research is proposed to encompass other mountain ranges in the northern hemisphere, aiming to evaluate whether the insights derived from the study of permafrost in the Alps and Scandinavia can be applied to different climatic and topographical contexts (Stewart-Jones and Gruber).

14Quantitative studies of permafrost in the Alps began with a focus on rock glaciers. These iconic periglacial formations have been the subject of boreholes since the 1980s, marking a significant turning point in our understanding of their stratigraphy and the temperatures influencing the frozen ground at depth. The Murtèl-Corvatsch rock glacier (2670 m a.s.l., Graubünden, Switzerland), where temperatures have been continuously measured since 1987, is a pivotal site in the Alps in this regard. The article by Haeberli et al. reviews the findings of this extensive dataset in a format that is accessible and engaging, titled “Frequently asked questions about permafrost.” For instance, it reveals that the thickness of Alpine permafrost far exceeds the depth of the instrumented boreholes (100 m), where the impacts of climate change over recent decades are already noticeable. The study elucidates that the temperature at 15–20 m (a depth at which seasonal variations are minimal) is warming at the same rate as the atmosphere (0.8 °C in 35 years) and that this warming will propagate to greater depths over the next few centuries, irrespective of future climate trends, significantly affecting the stability of the rock slopes. The contribution by Pogliotti et al. presents the results of permafrost monitoring, encompassing surface and deep boreholes, initiated a decade to 15 years ago at various high-altitude sites (3100–4450 m a.s.l.) in the Aosta Valley (Italy). Similarly, an average warming of 0.2 to 0.4 °C per decade is observed at depth, along with a deepening of the active layer by 2 m per decade. The authors underscore that data collected at very high altitudes illustrates a potential discrepancy in warming relative to altitude, with more significant warming at higher elevations. The contribution by Magnin et al. deals with the past 18 years of permafrost studies in the Mont Blanc massif and the opportunities they present for addressing practical challenges, whether in regional planning, geotechnical requirements, or risk mitigation for mountain sports enthusiasts. Among the outstanding questions is the quantification of water infiltration and its effects on permafrost-affected rock faces, as well as the estimation of the ice content in these terrains. In the past few decades, the Alps and Scandinavia have been the focal points of advanced work aimed at characterising permafrost and its evolution. Nonetheless, it is crucial to apply this knowledge to other mountainous regions worldwide, serving as input for modelling work, particularly for understanding the relationship between permafrost and rock avalanches. With this objective, Stewart-Jones and Gruber have developed a methodological framework for comparing regional climates and highlighting similarities and differences, with the aim of assessing to what extent knowledge of permafrost gained in specific geographic areas can be extrapolated to other regions. Through a comparison between the mountains of western Canada and areas affected by permafrost in Europe, they conclude that the use of Alpine and Scandinavian data is not applicable in Canada, given the greater heterogeneity of permafrost-affected terrain. This suggests the importance of establishing local monitoring programs to characterise permafrost on a finer scale in Canada.

15Two innovative contributions shed light on the risks associated with ongoing changes in the cryosphere. Firstly, all the large-scale rock and serac collapses that have occurred during the winter season (December-January) are documented in the Italian Alps (Chiarle et al.). Secondly, the risks faced by climbers using the two primary access routes to the summit of Mont Blanc have been precisely quantified over multiple recent summer seasons. This assessment compares the number of climbers using these routes (vulnerability) with the threats posed by rock and serac falls (hazard) along these routes (Ravanel et al.).

16Rock (and ice) falls affecting high mountains are far less frequent during the winter compared to other seasons, with the highest occurrence in summer (especially for altitudes above 2500 m a.s.l.). In contrast, winter events tend to be larger than those during other times of the year, primarily due to the inclusion of snow. Additionally, the late autumn represents the peak of the summer heat wave’s penetration, which can destabilise substantial volumes of rock. Therefore, winter events pose a higher risk to infrastructure. Although the inventory presented by Chiarle et al. includes a limited number of events (n=12), which does not allow for detailed statistical analysis, it seems reasonable to suggest that major events at high altitudes in permafrost-affected areas have primarily occurred in the recent period since 1997. This could be attributed to a shift in the triggers for winter events, transitioning from precipitation control to temperature control from the 2000s onwards. Mountaineers are the main users of high mountains, and they are the first to experience the effects of changing snow conditions and alterations in route geomorphology. As the highest point in Western Europe, Mont Blanc holds an iconic status and attracts thousands of climbers each year, numbering more than 20,000. The study conducted by Ravanel et al. provides the first-ever assessment of the risks incurred by climbers on the two primary access routes to the summit, including the notorious and accident-prone Goûter normal route. These two routes are exposed to different types of hazards: rockfalls for the Goûter route and serac falls for the Trois Monts route. An innovative methodology was employed, combining data from pyroelectric sensors to quantify passage and seismic sensors to record rockfalls in the Goûter couloir. Automatic photography was used for the Trois Monts route. The results reveal that the individual risk of death for the Trois Monts route is much lower that of the Goûter route. However, in both cases, the risk is considered to be within the threshold of “tolerable” regarding social acceptability of risk in France.

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Ludovic Ravanel, Melaine Le Roy, Florence Magnin et Marta Chiarle, « The Glaciated Slopes of the High Alpine Mountains: Holocene Evolution and Impacts of the Current Climate Crisis »Journal of Alpine Research | Revue de géographie alpine [En ligne], 111-2 | 2023, mis en ligne le 02 novembre 2023, consulté le 25 mars 2025. URL : http://journals.openedition.org/rga/12294 ; DOI : https://doi.org/10.4000/rga.12294

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Auteurs

Ludovic Ravanel

EDYTEM, Université Savoie Mont-Blanc, CNRS (UMR 5204)

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Melaine Le Roy

EDYTEM, Université Savoie Mont-Blanc, CNRS (UMR 5204)

Florence Magnin

EDYTEM, Université Savoie Mont-Blanc, CNRS (UMR 5204)

Articles du même auteur

Marta Chiarle

Italian National Research Council, Research Institute for Geo-Hydrological Protection (CNR-IRPI)

Articles du même auteur

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