Christophe Lambiel

Active layer increase may contribute to greenhouse gas emissions, ecosystem change, and increased hazards. Here, we show the results of field measurements of active-layer thickness from 156 monitoring sites in Arctic, Antarctic and mountain permafrost regions. Active layer thickness increased significantly at 55% and 38% of sites in the Arctic and Antarctic regions, at more than 90% European mountain and high elevation Asian sites, and at sites in South America, demonstrating worldwide permafrost degradation during the first quarter of this century (2000–2024). The largest changes were observed in mountain regions where active layer doubled at several sites. The smallest changes were observed at sites with thick surficial organic horizons and high ground ice content. In continuous permafrost, sites generally exhibited smaller increases compared to sites in discontinuous permafrost. Regression analysis indicates Arctic active layer changes are attributable to increasing thawing degree-days, followed by increases in total rainfall. Other permafrost regions require more sites and longer time-series to draw conclusions regarding active layer change attribution.

Mountain permafrost, constituting 30% of the global permafrost area, is sensitive to climate change and strongly impacts mountain ecosystems and communities. This study examines 21st century permafrost warming in European mountains using decadal ground temperature data from sixty-four boreholes in the Alps, Scandinavia, Iceland, Sierra Nevada and Svalbard. During 2013–2022, warming rates at 10 metres depth exceed 1 °C dec⁻¹ in cases, generally surpassing previous estimates because of accelerated warming and the use of a comprehensive data set. Substantial permafrost warming occurred at cold and ice-poor bedrock sites at high elevations and latitudes, at rates comparable to surface air temperature increase. In contrast, latent heat effects in ice-rich ground near 0 °C reduce warming rates and mask important changes of mountain permafrost substrates. The warming patterns observed are consistent across all sites, depths and time periods. For the coming decades, the propagation of permafrost warming to greater depths is largely predetermined already.

This is a correction for Kellerer-Pirklbauer et al (2024 Environ. Res. Lett. 19 034022).

Cryospheric long-term timeseries get increasingly important. To document climate-related effects on long-term viscous creep of ice-rich mountain permafrost, we investigated timeseries (1995–2022) of geodetically-derived Rock Glacier Velocity (RGV), i.e. spatially averaged interannual velocity timeseries related to a rock glacier (RG) unit or part of it. We considered 50 RGV from 43 RGs spatially covering the entire European Alps. Eight of these RGs are destabilized. Results show that RGV are distinctly variable ranging from 0.04 to 6.23 m a⁻¹. Acceleration and deceleration at many RGs are highly correlated with similar behaviour over 2.5 decades for 15 timeseries. In addition to a general long-term, warming-induced trend of increasing velocities, three main phases of distinct acceleration (2000–2004, 2008–2015, 2018–2020), interrupted by deceleration or steady state conditions, were identified. The evolution is attributed to climate forcing and underlines the significance of RGV as a product of the Essential Climate Variable (ECV) permafrost. We show that RGV data are valuable as climate indicators, but such data should always be assessed critically considering changing local factors (geomorphic, thermal, hydrologic) and monitoring approaches. To extract a climate signal, larger RGV ensembles should be analysed. Criteria for selecting new RGV-sites are proposed.

In this study, we inventoried and mapped the active and transitional rock glaciers in the central part of the Southern Alps, New Zealand, using Sentinel-1 InSAR (interferometric synthetic aperture radar) data. We used forty-three interferograms acquired between 2015 and 2019 with time intervals between six days and two years along with orthoimage analyses. A total of 123 rock glaciers were identified, of which 40 are active; that is, displaying velocities higher than 10 cm/yr. The remaining landforms are considered transitional. Among the complete sample of rock glaciers inventoried, 9 may also be interpreted as debris-covered glacierets. The number of inventoried landforms is low compared to what is observed in other similar mountain ranges, such as the European Alps. We explain this by the reduced vertical extent of the periglacial belt and the generally steep topography often not favorable for rock glacier development. Additionally, the motion rates appear relatively low. We hypothesize that a mean annual air temperature at the rock glacier locations well above 0°C is the main reason for this. These conditions may have resulted in significant ground ice melt. Rock glaciers in the Southern Alps are thus in an inactivation phase, which is expressed by typical morphologies such as stable fronts.

Rock glaciers are key landforms of the Alpine periglacial environment that transfer large amounts of debris. To improve our knowledge of the variation in permafrost creep rates over the Holocene, we combined data on current surface movements with surface dating on two adjacent rock glaciers in the Western Swiss Alps, the so-called Yettes Condjà B and C rock glaciers (hereafter YC-B and YC-C). Surface movements have been monitored since 2000 using GNSS measurements, and since 2016 by complementary UAV surveys and daily oblique photographs taken by a webcam. Furthermore, we used Optically Stimulated Luminescence (OSL) for dating block samples in the front of both rock glaciers and Schmidt hammer exposure-age dating (SHD) on different transects.YC-B is a very active landform that has developed on a steep and regular slope directly at the foot of a rock wall. Surface velocities display substantial interannual variations, from 0.4 m/a between 2005 and 2007, up to 3.5 m/a in 2015 and 2020. Cumulative displacements reached up to 49 m in 21 years. During the last decade, the rock glacier has been separated into two distinct parts by the progressive appearance of a scar in the steepest part of the landform. This suggests the onset of a destabilization phase of the rock glacier. In contrast, YC-C is much less dynamic, and its morphology and topography are more complex than YC-B. Its roots are occupied by a small debris-covered ice patch, and geophysical surveys suggest a high ice content in the landform. Velocities are much lower than in YC-B, with values between 0.1 and 0.4 m/a in the lowermost active sector. During the last 21 years, the cumulative displacement has been up to 6.5 m.SHD revealed ages of around 7.00 to 9.00 ka towards the front of both rock glaciers, while OSL dating in the front yielded ages of 8.00 to 12.00 ka. Thus, the two rock glaciers would have started to develop during the Early Holocene (11.70–8.24 ka b2k), i.e. before the Holocene Thermal Maximum which, in the Alps, is dated between 9.55 and 6.35 ka b2k. Combining these ages with the length of the rock glaciers, we obtain a mean Holocene velocity of 0.3 m/a for YC-B and 0.4 m/a for YC-C. There is thus a strong discrepancy between the rock glacier ages and the current surface velocities, especially for YC-B. Indeed, the estimated mean velocities during the entire Holocene are two orders of magnitude lower than the current velocities for this rock glacier. This indicates a considerable increase in velocities in recent decades and that current creep rates are probably unprecedented. More generally, this raises several questions about the velocity variations of rock glaciers on a Holocene timescale.

During the last two decades, the interest in the heritage values of geodiversity, mainly related to geology and geomorphology, has increased (Reynard and Brilha, 2018). Among the different methods used to analyse the geodiversity, geomorphological mapping can be considered as one of the main tools for the inventorying, assessment and valorisation of geoheritage sites.In this study, we compared two legend systems to analyse the contribution of each to the representation and mapping of various geomorphological landscapes. The two legend systems considered are the UNIL (University of Lausanne) legend and the CGMED-Tunisia (Laboratoire de Cartographie Géomorphologique des Milieux, des Environnements et des Dynamiques) legend. Both were used to map four sectors: (i) the Sebkhet Oum Ez-Zessar Ramsar site on the Gulf of Gabes coastline and (ii) the Wadi K'hil watershed on the Dahar Plateau, both located in south-eastern Tunisia, (iii) the Ferpècle glacier forefield and (iv) the Sanetsch area, both located on either side of the Upper Rhone valley in the Western Swiss Alps.In addition, the combination of the contributions of these two legends has made it possible to elaborate a geotouristic legend (Ghram Messedi et al., 2021) and, from this, to produce four geotouristic maps. These maps emphasise the geoheritage and geotouristic interests of Sebkhet Oum Ez-Zessar and Wadi K'hil, which fall within the perimeter of the UNESCO Dahar geopark project in Southeast Tunisia, as well as the importance of the Ferpècle glacier forefield geosite, part of which is listed in the federal inventory of alluvial areas of national importance illustrating rapid climate change, and the Sanetsch glacier-karst area listed in the inventory of Swiss geosites.Key-words: Geomorphological mapping, Geotourism maps, Tunisia, Switzerland.ReferencesGhram Messedi A., Ben Fraj T., Ben Ouezdou H., Clivaz M., Comisso C., Lambiel CH., & Reynard E., 2021: De la carte géomorphologique à la carte géotouristique : Proposition et application d’une méthode de représentation cartographique par SIG. Géomorphologie : relief, processus, environnement, vol. 27, n° 1, p. 69-87, DOI:10.4000/geomorphologie.15394Reynard E. & Brilha J., (ed) 2018: Geoheritage: assessment, protection and management. Elsevier, Amsterdam, 450 p.

Climate change leads to deep modifications of high Alpine environments. Those modifications have significant consequences on mountaineering itineraries and make them technically more difficult and more dangerous. Although a growing number of studies have recently documented this issue, they only list the processes affecting the itineraries and do not document their characteristics. Therefore, the acquired data lack relevance to be spread and for prevention making among climbers. In the present study, on the basis of the processes identified in previous studies in the Mont Blanc massif, we developed a legend in order to map the processes related to climate change that affect the itineraries and modify their climbing parameters. Following the UNIL geomorphological legend and using the same color code, 21 symbols were defined to map 23 processes. In order to evaluate the applicability and interest of the legend proposed, we present a first application in the Valais Alps (Switzerland), based on 21 semi-structured interviews with local Alpine guides and hut keepers. The map then allowed to list the processes affecting each of the 36 itineraries studied. On average, an itinerary is affected by 9 different processes and 25% of the itineraries have greatly evolved, which means their ascent in summer cannot be recommended anymore because of climate change. More generally, this legend would provide a common methodological basis, destined to be completed within future studies and to be relevant beyond the European Alps. This basis would also ease the comparability and compilation of results from different future studies.

In high alpine geomorphological research, different technologies are increasingly used to describe and monitor mass movements such as rock glaciers. Among them, the combination of Unmanned Aerial Vehicle (UAV) systems and Structure from Motion (SfM) techniques is gaining continuous interest due to rapid technological developments. In this study, we test the capability of repeated UAV surveys to accurately survey rock glacier deformation in the Lac des Vaux area, Valais Alps. The studied landform is located on a typical anthropic alpine environment in the Swiss Alps, where ski facilities and alpine tracks are a commonplace. A DJI Phantom 4 RTK UAV was flown twice in September 2019 and September 2020 to cover an area of about 0.25 km2 with nearly 1000 images each time. Differential corrections using a Virtual Reference Station (VRS) provided image geotags with centimetre-level accurate 3-D coordinates, thereby allowing dispensing with ground control. High-resolution orthomosaics and high-density point clouds are derived from the UAV-RTK surveys using a standard SfM processing workflow. The corresponding point clouds' accuracy was evaluated and adjusted based on stable terrain, reducing the 3-D alignment errors to a mean of 0.02 m. Elevation changes and surface kinematics in the rock glacier complex and its margins were quantified using point cloud operations and image correlation techniques. The results indicate that the landform has at least eight different lobes with mean velocities ranging between 0.1 and 1.3 m yr-1. The high-resolution analysis also permitted identifying moving lobes without morphological expression and small thermokarst depressions on the ski slope structure that traverses the rock glacier's active zone. Without relying on ground control, our approach achieves horizontal and vertical accuracies nearly as good as monitoring techniques using more traditional differential GNSS devices.