Comment on esurf-2022-48

Erosion at rock glacier fronts can supply sediment to adjacent torrents, which can be mobilized as damaging debris flows. Understanding the mechanisms which govern this erosion process is therefore critical for hazard management in affected areas. Previous research shows that rock glacier advance and liquid water input are the two main drivers of erosion at rock glacier fronts. However, earlier studies that calculated erosion volumes at rock glacier fronts were limited to temporal resolutions ranging from months to years. Therefore, these studies exhibit a high uncertainty due to the opposing influences of rock glacier front advance and retrogressive erosion. This prevented an in-depth understanding of the underlying drivers of these processes and their magnitudes on a short timescale. To overcome this limitation, we adapt the setup by Aaron et al. (2023) and use a permanently installed LiDAR sensor to monitor surface changes at a rock glacier front. By calculating Digital Elevation Models of Difference (DoDs) with respect to the local surface normal, we are able to compute erosion volumes at an hourly temporal resolution. This enables the quantification of short-term and small-scale geomorphic changes at the rock glacier front, which could not be detected by previous studies.Our study site is the fast-moving Ritigraben rock glacier (front velocity > 1cm/day) in the Mattertal (Valais). Its front is directly connected to a torrential channel, which regularly produced debris flows in the past and has been monitored for more than 30 years. Preliminary results show a link between erosion events and short-term precipitation with camera images showing signs of surface runoff in the affected areas. However, erosive events are triggered by comparatively common rainfall events. Small-scale reworking of material at the rock glacier front also occurs completely independently of precipitation events in some cases. Further investigation is needed to determine if the release of material is due to failure disposition from prior events and the rock glacier creep, or the influence of meltwater from the rock glacier body. ReferencesAaron, Jordan, Raffaele Spielmann, Brian W. McArdell, and Christoph Graf (2023). “High-Frequency 3D LiDAR Measurements of a Debris Flow: A Novel Method to Investigate the Dynamics of Full-Scale Events in the Field”. In: Geophysical Research Letters 50.5. doi: 10.1029/2022GL102373.

<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>

Rock glaciers are cryo‐conditioned downslope‐creeping landforms in high mountains. Their dynamics are changing due to external factors influenced by climate change. Although there has been a growing scientific interest in mountain permafrost and thus in rock glaciers in recent years, their historical development, especially before the first alpine‐wide aerial image flights in the 1950s, has hardly been researched. Therefore, we utilize a historical stereophotogrammetric map from 1922 and historical flow velocity profiles (1938–1953) and relate them to data derived from historical aerial photographs and airborne laser scanning data in several time slices between 1953 and 2021. By doing so, the development of flow velocity, surface elevation changes, and frontal advance of the two lobes of the composite rock glacier Inner Ölgrube, Kaunertal, Austria, is analyzed and compared over almost a century. Results indicate an increased frontal advance in the laterally confined area of one lobe and a severe subsidence in the upper area of both lobes between 1922 and 1953. Whereas the former could be explained by a combination of the short warm phase in the 1940s and 1950s and the (subsurface) topography, the latter might be attributed to the strong melting of superimposed debris‐covered dead ice bodies, a relict of the Little Ice Age (LIA) glaciation. Both factors might also contribute to the increased flow velocities between 1938 and 1953, which are still recognizable in the 1953–1970 time step. Although both lobes follow a general similar trend, which is in line with the alpine‐wide trend of flow velocity acceleration in the 1990s, differences in the geomorphic development of the two lobes were identified. In addition to a slightly varying evolution of the flow velocities, the timing and magnitude of the volume changes are different. Furthermore, both lobes display a dissimilar mechanism of frontal advance over the entire study period. Because the external forcing is identical, the varying development might be attributed to variations in internal structure, bedrock topography, or upslope connection of the lobes. Due to the lateral constriction, the subsurface topography, and the LIA maximum extent of the glacier, it is assumed that the geomorphic development of the Innere Ölgruben rock glacier, particularly before 1953, represents a special case, and the results are not simply transferable to other rock glaciers.

Rock glaciers are a periglacial phenomenon occurring in alpine regions. Their life cycle consists of a complex interaction of topographical, geological, hydrological, and climatic factors. In the light of a rapidly changing climate, the evolution of rock glaciers is of specific interest, as destabilizing rock glaciers may pose a potential hazard for high alpine infrastructure. In our contribution, we unravel the dynamics of a rock glacier located in Kühtai, Tyrol, within the Austrian alps, enveloped by steep mountain flanks. Directly below the rock glacier lies a hydropower reservoir, making the characterization, behaviour and stability of the rock glacier of specific interest for local stakeholders. Thus, we apply an integrated multi-methodical remote sensing monitoring approach encompassing Terrestrial Laser Scanning (TLS), UAV-Photogrammetry (UAV-P), Ground-based InSAR (GB-InSAR) and DGPS.The TLS and UAV-P measurements reveal ongoing acceleration of the rock glacier and revealing areas of differential displacement rates and activity, with certain areas. The differential acceleration of the rock glacier is especially pronounced indicating an ongoing detachment of the front. Furthermore, the GB-InSAR showed spatiotemporal variations of the different sections depending on varying meteorological boundary conditions. DGPS measurements were conducted to evaluate and verify the accuracy of the measured displacement rates of the remote sensing dataset.Detailed geological, geomorphological and hydrological mapping was performed on and around the rock glacier, to provide a comprehensive understanding of the geological and geomorphological context and the possible factors influencing the rock glacier's activity. UAV-P and TLS allowed to acquire structural data from inaccessible sections of the rock glacier and the steep adjoining rock walls. The structural data allowed to assess potential failure mechanisms of the rock slope and allowed to determine the source areas and volumes of continuous material supply from the rock walls on the rock glacier.In this study, preliminary results on annual, interannual and diurnal flow velocity variations of Finstertal rock glacier, based on GBInSAR, are presented, and compared to annual variations derived from UAV-P and TLS data. Thereby, our study contributes to the understanding of rock glacier dynamics in alpine environments. These findings help to deduce future developments of the rock glacier and to assess potential impacts on the surrounding landscape and infrastructure.

A Digital Twin (DT) is an accurate virtual representation of a physical object, phenomenon, or process. DTs are utilized in geosciences to simulate and analyze complex terrains. Developing DTs of rock glaciers is essential due to their significant role in addressing challenges related to climate change, monitoring permafrost, water resource management, and the dynamics of mountain ecosystems. Creating a DT of a rock glacier is very challenging because of the monitoring strategy (regarding spatial, temporal, and spectral resolution), the selected tools for processing, analyzing, and simulating data collected, and the computational infrastructure.  In this work, we study the rock glacier of Lazaun, South Tyrol, Italy (southern Ötztal Alps). The actively moving rock glacier (elevation range 2,480 to 2,700 m a.s.l.; 0.12 km2) is a prominent site for long-term monitoring and research, being one of the most investigated rock glaciers worldwide in terms of internal structure, motion, and hydrological behaviour.Here, we present a scale-down strategy starting from remote sensing products using differential synthetic aperture radar interferometry (DInSAR) to analyze extensive areas and identify active zones. Over these identified zones, we introduced a proximal sensing approach using drones equipped with specialized sensors.Using high-resolution cameras, we captured and combined overlapping images through photogrammetry techniques to generate detailed orthomosaics, 3D models, and Digital Surface Models. Additionally, we incorporated thermal imaging from UAV sensors to detect land surface temperature variations, inspect the presence of subsurface ice, and identify areas of activity.These data sources offer unparalleled spatial resolution and detail, which is crucial for building an accurate DT. Using GNSS to determine displacement and velocity, we continued a long-lasting in-situ method to measure the coordinates of specific features (boulders). We integrate ground photography to identify their shapes in drone products for further automatic shape identification.Finally, we introduced the use of FLAC3D (Fast Lagrangian Analysis of Continua for 3D modeling) to understand the propagation and evolution of the rock glacier movement by using a viscous constitutive model whose parameters have been calibrated by matching the velocity field of the central part of the glacier. We propose the use of Azure Digital Twins tool to visualize the possible combinations of data and scenarios. 

Rock glaciers and protalus ramparts are characteristic landforms of the periglacial domain often used as markers for the occurrence of permafrost in mountain terrains. As such, relict rock glaciers can be used for paleoclimate reconstructions. We present here the first previously unreported rock glacier inventory of the south-eastern Alps (including the north-eastern-most region of Italy and Slovenia), interpreted from high resolution orthophotos and a high resolution digital terrain model interpolated from airborne laser scanning (LiDAR). We mapped 53 rock glaciers covering a total area of 3.45km2. The majority of rock glaciers are classified as relict and distributed between 1708 and 1846ma.s.l. with slope ranging between 19° and 27°. In addition to rock glaciers we observed 66 protalus (pronival) ramparts, having median elevation of 1913ma.s.l. and covering 0.48km2. More than half of the inventoried protalus ramparts are located in the more maritime area of the Alps with higher precipitation compared to the location of rock glaciers. Using paleoclimate reconstruction based on the 1981–2010 climatological record of the area, we infer that the rock glaciers formed during one of the dry and cold periods of the late Pleistocene and early Holocene. Possible evolution of the active pronival forms observed in the most maritime area of this alpine sector is also discussed.

The link between rock glacier velocity and climatic forcing is well established in permafrost research, especially for rock glaciers. This understanding underpins the inclusion of rock glacier velocity as an associated parameter of the Essential Climate Variable “Permafrost” within the Global Climate Observing System since October 2022. In this context, the rock glacier velocity (commonly abbreviated as RGV) is defined as a spatially averaged interannual horizontal velocity time series related to a RG unit or a part of it. However, RGV does not invariably track climatic forcing in a simple, linear manner, which can obscure the climatic signal. In this study, we combine primarily multi-decadal RGV monitoring with long-term observations of ground surface and near-surface temperatures, as well as spring water temperatures, at two sites in the Hohe Tauern, Austrian Alps: the Dösen rock glacier (DOE) and the Hinteres Langtalkar rock glacier (HLK). Both are well-developed, typical alpine rock glaciers. Each features a dominant rock glacier spring that drains runoff from the landform and its contributing hydrologal catchment. Annual in-situ geodetic surveys began in 1995 (DOE) and 1999 (HLK). Ground surface and near-surface temperatures, along with several meteorological variables, have been monitored using miniature temperature loggers and standard meteorological sensors since 2006 at both sites. Spring water temperature monitoring started in 2016 at DOE and 2017 at HLK. Our results indicate a clear relationship, in part, between RGV and temperature (air, ground, water). However, this relationship weakens or disappears where geodetic points are not, or are only partially, representative of permafrost creep. Moreover, summer spring-water temperatures can be damped by heat exchange with internal ice, such that melt of the ice component buffers water peak temperatures. These findings underscore the importance of parallel, co-located monitoring of ground, water, and air temperatures (and other climatic parameters), alongside carefully designed geodetic sampling that targets zones of active permafrost creep.

La utilización de técnicas liquenométrlcas en el glaciar rocoso activo de Skjóldalur I (Islandia) ha permitido cuantifcar la existencia de importantes diferencias en su dinámica superficial. El estudio se llevó a cabo partiendo de un muestreo suficientemente representativo constituido por una malla de 48 puntos de control repartidos por la superficie del glaciar rocoso. En cada una de las localidades se obtuvieron medidas de los diez diámetros más largos de Rhizocarpon geographicum (s.L) y de sus porcentajes de cubrimiento. El tratamiento estadístico de los datos (a partir de la realización de un análisis de la varianza tri-direccional y de tests de significación no-paramétricos) confirmó la presencia de líneas de flujo preferencial en las pautas de movimiento del glaciar rocoso, atribuibles a una distribución irregular del núcleo interno de hielo.

In the second half of the 20th century, the western Antarctic Peninsula recorded the highest mean annual air temperature rise in the Antarctic. The South Shetland Islands are located about 100 km northwest of the Antarctic Peninsula. The mean annual air temperature at sea level in this Maritime Antarctic region is close to −2 °C and, therefore, very sensitive to permafrost degradation following atmospheric warming. Among geomorphological indicators of permafrost are rock glaciers found below steep slopes as a consequence of permafrost creep, but with surficial movement also generated by solifluction and shallow landslides of rock debris and finer sediments. Rock glacier surface velocity is a new essential climate variable parameter by the Global Climate Observing System, and its historical analysis allows insight into past permafrost behavior. Recovery of 1950s aerial image stereo-pairs and structure-from-motion processing, together with the analysis of QuickBird 2007 and Pleiades 2019 high-resolution satellite imagery, allowed inferring displacements of the Hurd rock glacier using compression ridge-and-furrow morphology analysis over 60 years. Displacements measured on the rock glacier surface from 1956 until 2019 were from 7.5 m to 22.5 m and surface velocity of 12 cm/year to 36 cm/year, measured on orthographic images, with combined deviation root-mean-square of 2.5 m and 2.4 m in easting and northing. The inferred surface velocity also provides a baseline reference to assess today’s displacements. The results show patterns of the Hurd rock glacier displacement velocity, which are analogous to those reported within the last decade, without being possible to assess any displacement acceleration.

Rock glaciers may appear to be stubby, slow-moving, debris-mantled cousins of glaciers, yet the controls on their formation, size, and persistence differ from those of glaciers. The defining rock glacier characteristic is a debris cover sufficiently thick to protect its icy core from ablation. We therefore model the controls on debris thickness, incorporating debris input, ice accumulation, and ice speed. We show that rock glaciers exist in a narrow range of conditions that provides both enough debris from eroding headwalls and enough ice from focused snow avalanches to create a small area of net accumulation. The deformation speed of the ice-rich rock glacier core sets the time available for accumulation of the protective cover. Quantitatively, a 100-m-tall headwall backwearing at 1 mm/yr produces a thick-enough debris cover only if rock glacier surface speeds at the exit of the avalanche zone are <1 m/yr. This low speed in turn limits the length of rock glaciers. Where surface ages have been constrained, rock glaciers are found to have originated in the early Holocene. There is only so far, typically hundreds of meters, rarely more than a kilometer, that rock glacier lobes can travel in the Holocene. The handover from glacial to rock glacial occupation of alpine valleys may involve complete deglaciation before rock glacier conditions are met. Finally, that the required rapid headwall retreat far outpaces vertical lowering rates of summits can explain observed strong ridgeline asymmetry.

Research Article| February 01, 1981 Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado STEVEN G. VICK STEVEN G. VICK 1Dames & Moore, Salt Lake City, Utah 84111 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1981) 92 (2): 75–84. https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation STEVEN G. VICK; Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado. GSA Bulletin 1981;; 92 (2): 75–84. doi: https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Some 23 rock glaciers have been identified in the central portion of the Mosquito Range. Surface features and characteristic forms correlate well with those reported for rock glaciers in Alaska and elsewhere in Colorado, New Mexico, and Utah. On the basis of air-photo interpretation, about two-thirds of the rock glaciers are lobate in form, and one-third are tongue-shaped. Only 5 of the 23 rock glaciers are believed to be active.A detailed stability analysis of two rock glaciers in Iowa Gulch indicates that landsliding of unstable morainal deposits played a major role in their formation. Landslide debris provided loading necessary to initiate ice creep in frozen till on the lower valley slopes. Ice creep continued, eventually bringing the rock glaciers to their present form. With the supply of landslide debris exhausted and with insufficient ice wedging and rock exposure to generate large talus cones, stresses generated by the superincumbent load were reduced by creep-induced spreading, and motion ceased. Internal ice, in the form of both interstitial ice and ice layers, still remains.Techniques developed to evaluate activity of rock glaciers in Alaska have been applied to the two rock glaciers in Iowa Gulch. These techniques, based principally on steepness and form of the rock glacier front as well as on calculated values of basal shear stress, indicate both rock glaciers to be inactive. Re-survey of a mining claim corner and inspection of a shaft show that no movement has occurred over the period of record and that the rock glaciers are indeed inactive, substantiating the usefulness and validity of the above-described techniques for assessment of rock glacier activity elsewhere. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abstract. Increased rates of glacier retreat and thinning need accurate local estimates of glacier elevation change to predict future changes in glacier runoff and their contribution to sea level rise. Glacier elevation change is typically derived from digital elevation models (DEMs) tied to surface change analysis from satellite imagery. Yet, the rugged topography in mountain regions can cast shadows onto glacier surfaces, making it difficult to detect local glacier elevation changes in remote areas. A rather untapped resource comprises precise, time-stamped metadata on the solar position and angle in satellite images. These data are useful for simulating shadows from a given DEM. Accordingly, any differences in shadow length between simulated and mapped shadows in satellite images could indicate a change in glacier elevation relative to the acquisition date of the DEM. We tested this hypothesis at five selected glaciers with long-term monitoring programmes. For each glacier, we projected cast shadows onto the glacier surface from freely available DEMs and compared simulated shadows to cast shadows mapped from ∼40 years of Landsat images. We validated the relative differences with geodetic measurements of glacier elevation change where these shadows occurred. We find that shadow-derived glacier elevation changes are consistent with independent photogrammetric and geodetic surveys in shaded areas. Accordingly, a shadow cast on Baltoro Glacier (the Karakoram, Pakistan) suggests no changes in elevation between 1987 and 2020, while shadows on Great Aletsch Glacier (Switzerland) point to negative thinning rates of about 1 m yr−1 in our sample. Our estimates of glacier elevation change are tied to occurrence of mountain shadows and may help complement field campaigns in regions that are difficult to access. This information can be vital to quantify possibly varying elevation-dependent changes in the accumulation or ablation zone of a given glacier. Shadow-based retrieval of glacier elevation changes hinges on the precision of the DEM as the geometry of ridges and peaks constrains the shadow that we cast on the glacier surface. Future generations of DEMs with higher resolution and accuracy will improve our method, enriching the toolbox for tracking historical glacier mass balances from satellite and aerial images.

Rock glaciers are a common landform in mountain areas with few or no glacier, which morphology reflects the deformation of an ice and debris mixture, and which response to climate changes raises many questions. Indeed, in a recent context of observed rock glacier destabilization or even collapse, the flow of the ice-rich permafrost on slope is the subject of various studies and surveys, especially with respect to the natural hazard they might represent. This paper presents the main results of the analysis of two terrestrial LiDAR surveys of the Laurichard rock glacier (French Alps), performed at a one year time lapse (2005-2006). This technique has allowed to acquire, at a sub-decimeter resolution, models of the rock glacier surface, which have been afterward compared together through two complementary approaches, in order i) to extract the small scale topography ; ii) to quantify the inter-annual surface changes ; iii) to determine the main characteristics of the rock glacier flow. The LiDAR-derived datasets were also compared to a digital terrain model of 1975 and to a geodetic data-sets of annual block position.

Abstract. Despite the abundance of rock glaciers in the Sierra Nevada of California, USA, few efforts have been made to measure their surface flow. Here we use the interferometric synthetic aperture radar (InSAR) technique to compile a benchmark inventory describing the kinematic state of 59 active rock glaciers in this region. In the late summer of 2007, these rock glaciers moved at speeds that range from 14 cm yr−1 to 87 cm yr−1, with a regional mean value of 53 cm yr−1. Our inventory reveals a spatial difference: rock glaciers in the southern Sierra Nevada moved faster than the ones in the central Sierra Nevada. In addition to the regional mapping, we also conduct a case study to measure the surface flow of the Mount Gibbs rock glacier in fine spatial and temporal detail. The InSAR measurements over this target reveal (1) that the spatial pattern of flow is correlated with surface geomorphic features and (2) a significant seasonal variation of flow speed whose peak value was 48 cm yr−1in the fall of 2007, more than twice the minimum value observed in the spring of 2008. The seasonal variation lagged air temperatures by three months. Our finding on the seasonal variation of surface speed reinforces the importance of a long time series with high temporal sampling rates to detect possible long-term changes of rock glacier kinematics in a warming climate.

Abstract. Glaciers and rock glaciers play an important role in the hydrology of the semi-arid northern Chile. Several studies show that glaciers have rapidly lost mass in response to climate change during the last decades. The response of rock glaciers to climate change in this region is, however, less known. In this study we use a combination of historical aerial photography, stereo satellite imagery, airborne lidar, and the Shuttle Radar Topography Mission (SRTM) DEM to report glacier changes for the Tapado Glacier–rock glacier complex from the 1950s to 2020 and to report mass balances for the glacier component of the complex, Tapado Glacier. Furthermore, we examine high-resolution elevation changes and surface velocities between 2012 and 2020 for 35 rock glaciers in the La Laguna catchment. Our results show how Tapado Glacier has shrunk by -25.2±4.6 % between 1956 and 2020, while the mass balance of Tapado Glacier has become steadily more negative, from being approximately in balance between 1956 and 1978 (-0.04±0.08 m w.e. a−1) to showing increased losses between 2015 and 2020 (-0.32±0.08 m w.e. a−1). Climatological (re-)analyses reveal a general increase in air temperature, decrease in humidity, and variable precipitation since the 1980s in the region. In particular, the severe droughts starting in 2010 resulted in a negative mass balance of -0.54±0.10 m w.e. a−1 between 2012 and 2015. The rock glaciers within the La Laguna catchment show heterogenous changes, with some sections of landforms exhibiting pronounced elevation changes and surface velocities exceeding that of Tapado Glacier. This could be indicative of high ice contents within the landforms and also highlights the importance of considering how landforms can transition from more glacial landforms to more periglacial features under permafrost conditions. As such, we believe high-resolution (sub-metre) elevation changes and surface velocities are a useful first step for identifying ice-rich landforms.