Relationship between geomorphological characteristics, environmental settings and activity of transitional rock glaciers: Insights from a statistical analysis in the French Alps

Field studies and examination of aerial photographs of approximately 200 rock glaciers in the Healy (1:250,000) quadrangle in the central Alaska Range showed that there are three types of rock glacier in plan: lobate, in which the length is less than the width (200–3500 feet long and 300–10,000 feet wide); tongue-shaped, in which the length is greater than the width (500–5000 feet long and 200–2500 feet wide); and spatulate, tongue-shaped but with an enlargement at the front. Lobate rock glaciers line cliffs and cirque walls and probably represent an initial stage; the other two move down valley axes and represent more mature stages. The rock glaciers are composed of coarse, blocky debris that is cemented by ice a few feet below the surface. The top quarter of the thickness is coarse rubble, below which is coarse rubble mixed with silt, sand, and fine gravel. Fronts of active (moving) rock glaciers are bare of vegetation, are generally at the angle of repose, and make a sharp angle with the upper surface. Fronts of inactive (stationary) rock glaciers are covered with lichens or other vegetation, have gentle slopes, and are rounded at the top. Active rock glaciers average 150 feet in thickness, inactive rock glaciers, 70 feet. The upper surface of most rock glaciers is clothed with turf or lichens. Sets of parallel rounded ridges and V-shaped furrows—longitudinal near the heads of some rock glaciers and transverse, bowed downstream, on the lower parts of others—and conical pits, crevasses, and lobes mark the upper surfaces of many rock glaciers. The upper surface of a rock glacier at the head of Clear Creek moved 2.4 feet per year between 1949 and 1957, and the front advanced 1.6 feet per year. Heights of the upper edges of the talus aprons along the fronts of rock glaciers average 45 per cent of the heights of the fronts. Each of these observations implies that motion is not confined to thin surface layers but is distributed throughout the interiors of the rock glaciers, which in this permafrost region are probably frozen. “Viscosity” has been calculated for rock glaciers at between 1014 and 1015 poises; for glacial ice it has been estimated at between 1012 and 1014 poises. Maximum average shear stresses within active rock glaciers range from 1 to 2 bars; these values are much larger than those calculated for solifluction and creep features. Rock glaciers occur on blocky fracturing rocks which form talus that has large interconnected voids in which ice can accumulate. They are rare on platy or schistose rocks whose talus moves rapidly by solifluction. The rock glaciers lie in an altitudinal zone about 2000 feet thick, centered on the lower limit of existing glaciers[1][1]. Although the firn lines on glaciers rise 1200 feet in a distance of 25 miles northward across the Alaska Range, the lower limit of active rock glaciers rises only 800 feet. The firn line on southward-facing glaciers is 2000 feet higher than that on northward-facing glaciers, yet in any given area southward-facing rock glaciers average only 200 feet higher than northward-facing rock glaciers. Insulation by the debris cover is believed responsible for the difference in altitudinal ranges between rock glaciers and glaciers. It is concluded that rock glaciers move as a result of the flow of interstitial ice and that they require for their formation steep cliffs, a near-glacial climate cold enough for the ground to be perennially frozen, and bedrock that is broken by frost action into coarse blocky debris with large interconnected voids. The longitudinal furrows are thought to result from the accumulation of ice-rich bands in the swales between talus cones at the head of the rock glaciers and the subsequent melting of this ice as the rock glacier moves down-valley. The transverse ridges are thought to result from shearing within the rock glacier that would occur where the thickness increases or the velocity decreases downstream. An average of 30 feet of bedrock was removed from source areas to form the present rock glaciers, indicating an average rate of erosion of 1–3 feet per year when they are active. [1]: #fn-1

<p>Active rock glaciers in Greenland have been studied since the 1980s focusing on two regions (Disko Island and Zackenberg) located north of 69°13’N. As judged from permafrost models, widespread existence of permafrost and thus active rock glaciers are also possible south of this latitude. Therefore, research on a large rock glacier on the island of Bjørneø (size: 1 km²; elevation 250-600 m a.s.l.; NNW-exposed) at 64°30’N was initiated in 2016. Research focused until 2020 on repeated differential GPS measurements at several fixed ground control points, on the analysis of the bottom temperature of the winter snow cover, and on the assessment of high-resolution orthophotos and digital terrain models based on UAV campaigns. Results up to 2020 indicate that permafrost influences a large part of the rock glacier and surface displacement takes place in the order of cm per year particularly in the central part.</p><p>Within an INTERACT research project we continued and expanded research at this rock glacier in 2021 applying two types of geophysics (electrical resistivity tomography, ground penetrating radar), differential GPS, relative surface dating, geomorphic mapping, clast form analysis, and monitoring of ground, air, and water temperatures. We find that widespread permafrost is likely along the measured geophysical profiles, that ground and water temperatures generally support the assumption of present permafrost conditions, and that the rock glacier evolved over a period of several thousand years, starting to form soon after the recession of the Greenland Ice Sheet from the coast some 10.4 to 11.4 ka BP.</p><p>In addition to fieldwork, different types of remote sensing- and modelling based research at this rock glacier were accomplished. Clast size distribution was semi-automatically quantified using a high-resolution digital terrain model. Results reveal distinct clast size-differences along a longitudinal profile of the rock glacier. Analyses of time-series of Sentinel-1 differential SAR interferograms for the period 2016 to 2021 showed minor motion in the uppermost part of the landform during a period of two months, distinct compressive flow (few cm) of two lobes of the landform after several months, and landform-wide movement over a period of 3 years. The terrain surface before the formation of the rock glacier, and thus the rock glacier volume, were reconstructed on the basis of field observations and terrain data. The volume of material relocated due to rock glacier activity was approx. 10 million m³. Finally, the present rock glacier extent and morphology were numerically reproduced as a steadily evolving and slowly moving viscous mass using a model implemented in the GIS-based open-source mass flow simulation framework r.avaflow.</p><p>Our chosen multidisciplinary approach is a significant step forward in understanding the long-term evolution and present conditions of large rock glacier systems in the low Arctic region of Greenland.</p>

Recent studies have demonstrated the rock glacier destabilisation and permafrost thawing induced by warming climate represent a continuous threat to life, infrastructure and socio‐economic development in the mountainous regions of the Hindu Kush Himalaya. This study presents the first systematic rock glacier inventory for the Shigar and Shayok basins, quantifying rock glacier geomorphology and kinematics based on morphological evidence using Google Earth images and interferometric synthetic aperture radar (InSAR). The certainty index of each inventoried rock glacier is recorded, along with its geomorphological properties and kinematic attributes. The rock glacier velocity is estimated through the InSAR time series analysis of Sentinel‐1 images from 2020 to 2021, with temporal baselines at 12‐day intervals. We developed a rock glacier inventory consisting of 84 rock glaciers covering an area of 29 km2 for the Shigar Basin and 2206 rock glaciers encompassing 369 km2 for the Shayok Basin. Among these rock glaciers, 69% and 52% are categorised as active rock glaciers, respectively. Rock glaciers in both catchments are confined to elevations between 3600 and 5875 m a.s.l., with a mean area of 0.22 km2. The maximum recorded velocity for active rock glaciers in the Shigar Basin is 101 ± 9 cm year−1, with a median of 27 ± 10 cm year−1, and in the Shayok Basin 114 ± 10 cm year−1 (median of 29 ± 9 cm year−1). Temporal variations in the surface velocities of the rock glaciers reveal that they increase with rising temperatures in both catchments, highlighting the seasonality in the rock glacier surface velocity. In total, we recorded the kinematic attributes of 98% of the inventoried rock glaciers in the study area.

ABSTRACTIn the Colorado Front Range, rock glacier distribution has been noted on U.S. Geological Survey maps and in several publications; however, a comprehensive account of distribution is not available. When analyzed in a Geographic Information System (GIS), Digital Elevation Model variables (elevation, slope, or aspect) could reveal unique topographic characteristics of rock glaciers. The objectives of this study are to provide an accurate, complete account of rock glacier locations in a digital format, to compare topographic variables of rock glacier form and activity classes, and to evaluate glacier and rock glacier topographic information. Rock glacier locations were obtained from previous studies and were re-digitized on high-resolution digital orthophotos. Glacier distribution was determined through classification of a satellite image. Topographic information for rock glacier form and activity classes as well as for glaciers was obtained through zonal overlay in a GIS. Results indicate that tongue-shaped rock glaciers occur at higher elevations, have more northerly aspects, and have gentler slopes compared to lobate rock glaciers. Active, inactive, and fossil forms showed typical elevation and aspect gradients. Active rock glaciers are found at the highest elevations and most northern aspects. Inactive rock glaciers are found at lower elevations on all aspects with a tendency to face northeast, and fossil rock glaciers occur at the lowest elevations on all aspects. Topographic variables for all rock glaciers were statistically different compared to glacier locations; however, active tongue-shaped rock glaciers had similar topographic variables compared to glaciers, but lobate forms showed a significant difference. In the Front Range, active tongue-shaped rock glaciers are developed by glacial processes and active lobate forms are the product of periglacial processes.

Rock glacier dynamics in Southern Carpathian Mountains from high-resolution optical and multi-temporal SAR satellite imagery

Abstract. In this study, we propose a methodology to estimate the spatial distribution of destabilizing rock glaciers, with a focus on the French Alps. We mapped geomorphological features that can be typically found in cases of rock glacier destabilization (e.g. crevasses and scarps) using orthoimages taken from 2000 to 2013. A destabilization rating was assigned by taking into account the evolution of these mapped destabilization geomorphological features and by observing the surface deformation patterns of the rock glacier, also using the available orthoimages. This destabilization rating then served as input to model the occurrence of rock glacier destabilization in relation to terrain attributes and to spatially predict the susceptibility to destabilization at a regional scale. Significant evidence of destabilization could be observed in 46 rock glaciers, i.e. 10 % of the total active rock glaciers in the region. Based on our susceptibility model of destabilization occurrence, it was found that this phenomenon is more likely to occur in elevations around the 0 ∘C isotherm (2700–2900 m a.s.l.), on north-facing slopes, steep terrain (25 to 30∘) and flat to slightly convex topographies. Model performance was good (AUROC = 0.76), and the susceptibility map also performed well at reproducing observable patterns of destabilization. About 3 km2 of creeping permafrost, or 10 % of the surface occupied by active rock glaciers, had a high susceptibility to destabilization. Considering we observed that only half of these areas of creep are currently showing destabilization evidence, we suspect there is a high potential for future rock glacier destabilization within the French Alps.

Rock glaciers result from the long-term creeping of ice-rich permafrost along mountain slopes. Under warming conditions, deformation is expected to increase, and potential destabilization of those landforms may lead to hazardous phenomena. Monitoring the kinematics of rock glaciers at fine spatial resolution is required to better understand at which rate, where and how they deform. We present here the results of several years of in situ surveys carried out between 2005 and 2015 on the Laurichard rock glacier, an active rock glacier located in the French Alps. Repeated terrestrial laser-scanning (TLS) together with aerial laser-scanning (ALS) and structure-from-motion-multi-view-stereophotogrammetry (SFM-MVS) were used to accurately quantify surface displacement of the Laurichard rock glacier at interannual and pluri-annual scales. Six very high-resolution digital elevation models (DEMs, pixel size <50 cm) of the rock glacier surface were generated, and their respective quality was assessed. The relative horizontal position accuracy (XY) of the individual DEMs is in general less than 2 cm with a co-registration error on stable areas ranging from 20–50 cm. The vertical accuracy is around 20 cm. The direction and amplitude of surface displacements computed between DEMs are very consistent with independent geodetic field measurements (e.g., DGPS). Using these datasets, local patterns of the Laurichard rock glacier kinematics were quantified, pointing out specific internal (rheological) and external (bed topography) controls. The evolution of the surface velocity shows few changes on the rock glacier’s snout for the first years of the observed period, followed by a major acceleration between 2012 and 2015 affecting the upper part of the tongue and the snout.

Recent progress in rock glacier studies is reviewed with some emphases on the competition between the glacial and periglacial hypotheses. Rock glaciers are tongue-shaped or lobate bodies composed of angular boulders that resembles a small glacier, usually accompanied by multiple transverse ridges resulting from a compressive flow. Rock glaciers are classified, in terms of the origin of surface materials, into talus and morainic rock glaciers, and in the light of the activity status, into active, inactive and fossil ones. The distribution of active rock glaciers are delimited by the regional glacier equilibrium line and lower limit of mountain permafrost.The internal structure of rock glaciers has been approached by direct observations and indirect geophysical soundings. In some rock glaciers, natural outcrops exhibit a massive ice body with debris bands beneath the surface boulder layer, which has encouraged the glacial hypothesis. Massive ice was also found in boreholes penetrating through a rock glacier permafrost in the Swiss Alps, despite being considered to originate from snow avalanche or refrozen meltwater. In fact, deformation occurred mostly in the frozen debris layer beneath the massive ice, indicating the periglacial origin of the rock glacier due to permafrost creep. Geophysical soundings, including seismic, geoelectric and gravimetric measurements, have provided useful information on the three-dimensional structure, stratigraphy and ice contents of rock glacier bodies, although authors preferring the glacial hypothesis tend to reject such indirect results. The origin of any rock glacier is thus equivocal without detailed analyses of internal stratigraphy and ice composition.Most of the active rock glaciers are moving at a speed of 101 cm yr-1, two orders of magnitude slower than 'ice' glaciers. The periglacial model attributes such a slow movement to permafrost creep. A possible consequence of this is that active rock glaciers usually have ages of several thousand years ; that inactive ones were activated repeatedly during the colder periods of the Holocene; and that fossil ones moved during the Late Glacial. In contrast, the glacial model explains that many rock glaciers originated from a debris-covered glacier during the Little Ice Age and have been loosing their ice content and speed rapidly with the 20th-Century warming.Only a few rock glaciers have been identified from Japanese mountains. Although locations favorable for active rock glaciers are restricted to the northern side of some high mountains, the mountain permafrost belt must have been wide enough to form a number of rock glaciers during some past cold periods. Subsequent permafrost melting would have fossilized these rock glaciers, some of which may have been misinterpreted as glacial moraines or protalus ramparts.

Rock glaciers represent typical periglacial landscapes and are distributed widely in alpine mountain environments. Rock glacier activity represents a critical indicator of water reserves state, permafrost distribution, and landslide disaster susceptibility. The dynamics of rock glacier activity in alpine periglacial environments are poorly quantified, especially in the central Himalayas. Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) has been shown to be a useful technique for rock glacier deformation detection. In this study, we developed a multi-baseline persistent scatterer (PS) and distributed scatterer (DS) combined MT-InSAR method to monitor the activity of rock glaciers in the central Himalayas. In periglacial landforms, the application of the PS interferometry (PSI) method is restricted by insufficient PS due to large temporal baseline intervals and temporal decorrelation, which hinder comprehensive measurements of rock glaciers. Thus, we first evaluated the rock glacier interferometric coherence of all possible interferometric combinations and determined a multi-baseline network based on rock glacier coherence; then, we constructed a Delaunay triangulation network (DTN) by exploiting both PS and DS points. To improve the robustness of deformation parameters estimation in the DTN, we combined the Nelder–Mead algorithm with the M-estimator method to estimate the deformation rate variation at the arcs of the DTN and introduced a ridge-estimator-based weighted least square (WLR) method for the inversion of the deformation rate from the deformation rate variation. We applied our method to Sentinel-1A ascending and descending geometry data (May 2018 to January 2019) and obtained measurements of rock glacier deformation for 4327 rock glaciers over the central Himalayas, at least more than 15% detecting with single geometry data. The line-of-sight (LOS) deformation of rock glaciers in the central Himalayas ranged from −150 mm to 150 mm. We classified the active deformation area (ADA) of all individual rock glaciers with the threshold determined by the standard deviation of the deformation map. The results show that 49% of the detected rock glaciers (monitoring rate greater than 30%) are highly active, with an ADA ratio greater than 10%. After projecting the LOS deformation to the steep slope direction and classifying the rock glacier activity following the IPA Action Group guideline, 12% of the identified rock glaciers were classified as active and 86% were classified as transitional. This research is the first multi-baseline, PS, and DS network-based MT-InSAR method applied to detecting large-scale rock glaciers activity.

Rock glaciers are the visible expression of mountain permafrost. The deformation of internal ice and basal horizon make them creeping downward, which allows their detection. Their geomorphological characteristics tend to evolve as a response to degrading permafrost conditions. If the internal ice is melting, the surface creeping gradually decreases until the landform stabilizes. This gradual deactivation has led to the definition of “rock glaciers in transition”. Recent studies highlighted a general trend of active rock glaciers’ increasing surface velocity in the last decades. In this context, we are asking if remaining ice in rock glaciers in transition could allow an increase of surface velocity trend similar to active rock glaciers? This study aims to describe rock glaciers in transition geomorphic settings and their present-day kinematics, and explore how their intrinsic and extrinsic characteristics can explain their activity. To answer this question, we applied remote sensing techniques from a French inventory of rock glaciers such as i) High resolution differential radar interferometry images to describe present days surface velocities for all “inactive” inventoried rock glaciers and reveal global trends at a large scale. ii) Geomorphic mapping of the rock glaciers characteristics such as their geometry, geomorphological and geological settings (rock glacier system, slope, latitude/longitude, altitude, concavities, vegetation cover, exposition, aspect and lithology of the blocks…). iii) By combining a dataset with i) and ii), we analyze correlations and dominant parameters using an MCA factorial analysis and a multimodal linear regression. Over 521 rock glaciers, 305 present displacements detectable from 30 InSAR images during summer period between 2016 and 2018. Most of them have velocities rates lower than 10 cm. yrˉ¹ (N=184), and for 1/3 (N=120) it ranges from 10 to 50 cm. yrˉ¹. Higher rates only concern 11 rock glaciers. For 80% of them (N=247), the mean surface area of displacements is lower than a half of the rock glacier surface area. The most represented geomorphic criteria are related to sagging landforms. Indeed, more than 50% of rock glaciers have a concave transversal profile matching with subsidence, whereas the others face with a high asymmetric topography. We support the hypothesis that lithology, exposition and the slope could be external factors that explains the most the heterogeneity of rock glaciers responses to a global climatic impact. The concavity/convexity index of transversal profiles, the surface slope and the vegetation cover should be the best parameters to describe the state of a transitional rock glacier in accordance with its activity. However, for many of rock glaciers with velocities ranging between 10 and 50cm. yrˉ¹ these criteria are met. Morphodynamical approaches are essential to better understand the link between external parameters and morphological settings of rock glaciers in transition, in responses to their activity. Nonetheless, the ice content and amount of water input can be essential drivers of rock glaciers activity. It is therefore important to complement such morphodynamical studies with an analysis of the subsurface in order to correlate these characteristics with the actual internal properties of rock glaciers.

<p>Recent acceleration of rock glaciers has been largely documented in the European Alps, hence highlighting an increase in flow speed of stable rock glaciers and some anomalous behaviors called destabilization (development of landslides-like features on the rock glacier surface).  In this study, we focus on Laurichard active rock glacier, 225 m long, up to 75 m wide, which covers an area of 0.084 km2 and has the longest measurement time-series in the French Alps. Here we aim to understand the causes of the changes in ice velocity of Laurichard rock glacier. We investigate the changes in the fluxes of ice masses across longitudinal and transversal profiles in order to be able to analyze in details the differences between the upper part and the front of the glacier. Using a combination of remote sensing data from 1952 (historical aerial images) until 2018 (Pléiades high-resolution satellite images), we documented the three-dimensional evolution of the Laurichard rock glacier during the last 60 years. We calculated the surface flow velocity between 1952 and 2018 using a feature-tracking algorithm at a resolution of 1 m and a precision of 0.5 m. Digital elevation models were assembled using the SfM techniques for aerial images, and the AMES stereo pipeline for Pléiades data. In addition, we made the analysis using in-situ annual velocities and temperatures data allowing to understand better which factors mostly explain the kinematic behavior.  We reconstructed a time series of changes in surface elevation by systematically co-registering and differencing DEMs between 1952 and 2018, with an average precision of 1 m. We first observed that the average annual horizontal velocity measured had increased progressively from 0.65 m yr<sup>-1</sup> to 1.1 m yr<sup>-1</sup> to 1.5 m yr<sup>-1</sup> for the periods 1952-1960, 1994-2003 and 2013-2018, respectively. On the other hand, the surface mass changes and long term monitoring of mass transport show for all analyzed periods a clear negative surface elevation change of 2 m on average, between 1952 and 2018. The area with most of the elevation changes is the frontal part of the glacier, which is consistent with the increase in speed, which represents a mass exchange from the upper part to the front. We conclude that the rates of rock glacier mass transport have increased during the last 20 years and hypothetize, for this rock glacier, a transition state controlled mainly by local topographical factors which will eventually lead to high speed rock glacier or rock glacier destabilization.</p>

<p>Rock glaciers are perennially frozen bodies of ice and rock debris that move downslope primarily due to deformation of internal ice. These features play an important role in alpine hydrology and landscape evolution, and constitute a significant water resource in arid regions. In the Uinta Mountains, Utah, nearly 400 rock glaciers have been identified on the basis of morphology, but the presence of ice has been investigated in only two. Here, I use satellite-based interferometric synthetic-aperture radar (InSAR) from the Copernicus Sentinel-1 satellites to identify and monitor active rock glaciers over a 10,000 km<sup>2 </sup>area. I also compare the time-dependent motion of several individual rock glaciers over the summers of 2016-2019 to search for relationships with climatic drivers such as precipitation and temperature. Sentinel-1 data from the August-October of 2016-2019 are used to create 79 interferograms of the entire Uinta range and are processed with the NASA/JPL/Stanford InSAR Scientific Computing Environment (ISCE) software package. Temporal baselines of intrayear interferograms range from 6-72 days. We use average velocity maps to generate an active rock glacier inventory for the Uinta Mountains containing 196 active rock glaciers. Average rock glacier velocity is 3 cm/yr in the line-of-sight direction, but individual rock glaciers have velocities ranging from 0.3-15 cm/yr. Rock glacier speeds do have a seasonal component, and were fastest in August across all years. One rock glacier reached a speed of 40 cm/yr over a 12 day interval from August 5 to August 17 of 2017. Preliminary results suggest that active rock glaciers are found at altitudes 10 m higher on average than inactive and relic rock glaciers identified in the previous inventory. Rock glacier movement did not accelerate between 2016 and 2019, suggesting that rock glaciers in this part of the Rocky Mountains are not speeding up over time. Our results highlight the ability to use satellite InSAR to monitor rock glaciers over large areas and provide insight into the factors that control their kinematics.</p>

Rock glaciers are widespread periglacial landforms in mountain regions like the European Alps. Depending on their ice content, they are characterized by slow downslope displacement due to permafrost creep. These landforms are usually mapped within inventories, but understand their activity is a very difficult task, which is frequently accomplished using geomorphological field evidences, direct measurements, or remote sensing approaches. In this work, a powerful method to analyze the rock glaciers’ activity was developed exploiting the synthetic aperture radar (SAR) satellite data. In detail, the interferometric coherence estimated from Sentinel-1 data was used as key indicator of displacement, developing an unsupervised classification method to distinguish moving (i.e., characterized by detectable displacement) from no-moving (i.e., without detectable displacement) rock glaciers. The original application of interferometric coherence, estimated here using the rock glacier outlines as boundaries instead of regular kernel windows, allows describing the activity of rock glaciers at a regional-scale. The method was developed and tested over a large mountainous area located in the Eastern European Alps (South Tyrol and western part of Trentino, Italy) and takes into account all the factors that may limit the effectiveness of the coherence in describing the rock glaciers’ activity. The activity status of more than 1600 rock glaciers was classified by our method, identifying more than 290 rock glaciers as moving. The method was validated using an independent set of rock glaciers whose activity is well-known, obtaining an accuracy of 88%. Our method is replicable over any large mountainous area where rock glaciers are already mapped and makes it possible to compensate for the drawbacks of time-consuming and subjective analysis based on geomorphological evidences or other SAR approaches.

Abstract. Rock glaciers, composed of debris and ice, are widely distributed across cold mountain regions worldwide. Although research on rock glaciers is gaining momentum, the distinct behaviour of rock glaciers in the marginal periglacial environments remains poorly understood. This study combines remote sensing and in situ methods to characterize transitional rock glaciers in the Carpathian Mountains. We used Persistent Scatterer Interferometry (PSInSAR) on Sentinel-1 images (2015–2020) to detect slope movements associated with rock glaciers and differential GNSS measurements (2019–2021) to track horizontal movement of 25 survey markers. Continuous ground temperature and winter snow cover bottom temperature (BTS) measurements examined energy exchange fluxes affecting these rock glaciers. Geophysical surveys (electrical resistivity tomography and refraction seismic tomography), and petrophysical joint inversion (PJI) quantified ice content in one rock glacier. PSInSAR identified 92 moving areas (MAs) with slow displacement (<5 cm yr−1) mostly between 2000 and 2300 m, where solar radiation was minimal. Near-surface thermal data from four rock glaciers suggest favourable conditions for permafrost persistence, largely driven by internal ventilation processes (e.g., advection heat fluxes) throughout the winter. BTS confirmed very low ground surface temperatures over much of the investigated rock glaciers, particularly in their upper parts and within the MAs. Geophysical investigations reveal ice-poor permafrost remnants in the Galeşu rock glacier, while PJI modelling estimated a low ground ice content (∼ 18 %) in its upper sector. At this site, surface displacements stem from active layer deformation, not permafrost creep. At two other sites, dGNSS markers moved consistently toward rock glacier fronts, indicating permafrost creep. Regarding activity status, the majority of rock glaciers in the Retezat Mountains were categorized as relict, with only 21 % classified as transitional. Transitional rock glaciers occur 150 m higher and are slightly smaller than relict ones.

<p>While the knowledge of the dynamics and internal structure of rock glaciers is well developed, a lack of understanding of their hydrological functioning is observed in the scientific literature. In particular, the origin and the quality of the water emerging from rock glaciers are not well known, together with its contribution to aquatic systems. Since rock glaciers are becoming increasingly important water sources under the influence of climate change, it is essential to improve knowledge about the modification of the hydrological regime of these high altitude debris accumulation, in particular by tracing ice melt in rock glacier outflows, and to quantify the impact of ground ice melting on the hydrochemistry of Alpine water systems. In this research, we combined isotopic and physico-chemical analyses for six rock glacier outflows in the Swiss Alps during the 2020 summer season. Chemical and isotopic analyses were also performed in sources not fed by rock glaciers at all study sites. The ionic content (SO<sub>4</sub><sup>2-</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>, NO<sub>3</sub><sup>-</sup>) measured in water emerging from active rock glaciers and ice-patches was higher than that detected in sources not fed by rock glaciers. Water emerging from active rock glaciers and ice-patches was also characterized by an increase in electrical conductivity and in ionic content (SO<sub>4</sub><sup>2-</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>), and by isotopic (δ<sup>18</sup>O) enrichment during the warm season. The seasonal evolution of these physico-chemical and isotopic parameters could indicate the water supply related to ground ice melting in water emerging from active rock glaciers and ice-patches. We assume that the cryosphere stored atmospheric pollutants and other chemical elements during a colder period in the recent past (1960s-1980s) and that the current melting of rock glacier ice releases these chemical compounds in the Alpine water systems. The hydro-chemical processes taking place in active rock glaciers were summarized in a conceptual model based on the results of this study.</p>