Dr. Robert Kenner

Observations in the European Alps show a long-term rise in rock glacier velocities, which is often associated with increased air and ground temperatures and, more recently, water content. Long-term rock glacier acceleration is superimposed by a high interannual variability of the velocity with a particular gap in the quantitative assessment of the role of water in rock glacier kinematics and the factors leading to short-term rock glacier deceleration.
To address this research gap, we drilled three vertical boreholes in the Schafberg rock glacier, Swiss Alps, in August 2020. We documented their stratigraphy and equipped one of the boreholes with temperature sensors and piezometers and the other two with cross-borehole electrodes for electrical resistivity tomography measurements. Rock glacier velocities were determined using repeated terrestrial laser scans. Using data from an additional borehole and nearby weather stations and ground surface temperature sensors, we analysed the interactions between meteorological and subsurface conditions during a rock glacier deceleration period, from January 2021 to July 2023.
Our findings show that a lowering of the water content in rock glacier shear horizons is crucial for interannual rock glacier deceleration. The impact of the snowpack, both as an insulator and as a water source, is significant for rock glacier kinematics. Winters with little snow and relatively dry summers appear to be ideal for rock glacier cooling and drying, leading to deceleration. Summer heat waves have limited impact on rock glacier velocity if they are preceded by snow-poor winters.
Our study uses an innovative combination of borehole data to gain insights into rock glacier temperatures and water contents, allowing us to detect relative changes in ice and/or water contents in ice-rich permafrost. The monitoring techniques used have the potential to contribute to a better understanding of the main drivers of rock glacier kinematics and water availability.

Ground temperatures in alpine terrain vary considerably over short distances, particularly due to differences in elevation and incoming short-wave radiation but also snow and surface conditions. To allow for direct cross-site, interregional, and cross-disciplinary comparisons, we introduce a parameter called the potential 0 °C isotherm (PZDI) in the ground. This parameter represents an aspect- and elevation independent geo-projection of ground temperatures. It was calculated for several ground temperature datasets from the (sub-)permafrost zone in the European Alps. We analyse the reaction of the PZDI at different depths to long-term changes in atmospheric temperature, represented by the atmospheric 0 °C isotherm (AZDI). The close correspondence of PZDI and AZDI mainly provided two new insights: Based on 15 boreholes, the PZDI/AZDI interaction allowed a depth-dependent analysis of the magnitude and temporal evolution of the disequilibrium between atmosphere and ground and the potential heat transfer processes involved. Moreover, it allowed a reconstruction of the development of ground temperatures in the European Alps during the second half of the 20th century, adding 50 years to the longest existing time series measured in ice-poor permafrost. This extension into the past reveals a major warming at the end of the 1980s, which occurred before the start of the available permafrost temperature observations. In the 1955–2021 period, the 5-year running mean of the AZDI rose by 400 m, while the PZDI at 15 m depth rose by about 300 m. Projecting this warming into a permafrost distribution map shows a decline in shallow, ice-poor permafrost area by roughly 60 % since the 1980s. We expect the PZDI to follow the AZDI and to increase by another 100 m in the coming decade and up to at least 14 m depth. This would increase the area with loss of shallow permafrost to approximately 80 % since the 1980s.

Am 14. April 2024 um 06:56 Uhr ereignete sich in der Westflanke des Piz Scerscen (Berninamassiv, Engadin, Graubünden) auf einer Höhe von 3640 m ü. M. ein grosser Bergsturz. Rund 5.5 Millionen m³ Fels und Gletschereis lösten sich, stürzten auf den darunter liegenden Vadret da Tschierva und rissen in der Sturzbahn eine dicke Schneedecke und grosse Mengen Gletschereis mit sich. Dieses Gemisch aus Gestein, Eis und Schnee floss über das Gletscherplateau, durch die darunterliegenden Eisfälle und zwischen den Seitenmoränen des Gletschers hinunter und erzeugte eine grosse Staubwolke, bevor es sich auf rund 2100 m ü. M. im Val Roseg, fast 6 km vom Anriss ablagerte. Das Ereignis forderte glücklicherweise keine Opfer und verursachte keine Infrastrukturschäden. In diesem Bericht beschreiben wir die Bedingungen, die zum Zeitpunkt des Ereignisses herrschten und nutzen die verfügbaren Informationen, um die Prozesse zu analysieren, die vor und während des Ereignisses stattfanden.

Im Zuge des Klimawandels kann auftauender oder sich auf nahe 0°C erwärmender Permafrost zu einer Häufung von Felsstürzen in steilem Gelände führen. Diese Studie hat deshalb steile Felshänge des Wallis in einem Temperaturbereich von -3°C bis 0°C auf ihr Gefährdungspotenzial für tiefer liegende Infrastrukturen untersucht. Dazu wurde die Präsenz von sensibler Infrastruktur im Gefährdungsbereich ebenso berücksichtigt wie die aus mehreren Einzelkriterien zusammengesetzte Wahrscheinlichkeit für Sturzereignisse. Zusammen ergeben beide Faktoren einen Risikohinweis für jeden Steilhangsektor im betreffenden Bodentemperaturintervall. Auf Grundlage dieses Risikohinweises zeigt sich, dass sich die potenzielle Gefährdung durch grosse Felsstürze aus warmem Permafrost auf 89 Standorte im Kanton Wallis beschränkt. Für diese Standorte wurde in Abhängigkeit des Risikos eine Rangliste erstellt, welche es den Naturgefahrenverantwortlichen ermöglicht, einen Fokus auf diese Gebiete zu legen sowie mit präventiven Massnahmen und Vorkehrungen eine Gefahrensituation frühzeitig zu erkennen.

Lidar measurements and UAV photogrammetry provide high-resolution point clouds well suited for the investigation of slope deformations. Today, however, the information contained in these point clouds is rarely fully exploited. This study shows three examples of large-scale slope instabilities located in Switzerland, which are actively monitored for reasons of hazard prevention. We used point clouds acquired by terrestrial laser scanning to (1) identify differences in kinematic behaviour of individual rock compartments; (2) highlight active shear planes within the moving rock mass; (3) define the kinematic process driving the slope displacements; (4) model basal sliding planes based on the 3D surface movements of rock slides; (5) calculate exact displacement angles, (6) provide estimates on destabilised rock volumes. This information has significantly contributed to the process understanding and has thus supported decision-making in hazard management.

Rising air temperatures and increasingly intense precipitation are being observed in the Swiss Alps. These changes strongly affect the evolution of the temperature regime and the dynamics of mountain permafrost. Changes occur at different rates depending on ground ice content. Long-term monitoring reveals progressive warming and degradation of permafrost and accelerating rock glacier velocities. This study analyses changes occurring in ice-rich (excess-ice) and ice-poor mountain permafrost in Switzerland between 1997 and 2019 on the basis of ground temperature and rock glacier dynamics measurements carried out by the WSL Institute for Snow and Avalanche Research SLF at seven sites. Long-term borehole data indicate an increase of ground temperatures at all depths, in particular at ice-poor and nearly snow-free sites. Active layers are thickening at most sites and prolonged periods of active layer thaw are observed. Long autumn zero curtains are observed in ice-rich permafrost, possibly leading to an overall acceleration of rock glaciers. All these changes point towards ongoing permafrost warming and permafrost degradation in future.

The landscape above Pontresina in the Eastern Swiss Alps is characterized by mountain peaks reaching around 3,000 m a.s.l, steep rock walls, ice-bearing scree slopes and dynamic rock glaciers in a corrie - all located above a precipitous gully leading down to the village. A strong visual impact is caused by the presence of over 15 km of avalanche defence structures and a large retention dam. These protection measures were progressively built over the past 130 years. The most recent ones are specially adapted for unstable permafrost conditions and to provide protection against both avalanches and debris flows triggered in over-steepened ice-bearing terrain. The Foura da l’Amd Ursina site (also known as Schafberg) above Pontresina displays the ideal implementation of research results in the development of practical solutions against natural hazards in a mountain environment undergoing climate-related changes.

Alpine permafrost is currently warming, leading to changes such as active layer deepening and talik formation. Frequency domain electro-magnetometry (FDEM) measurements were tested as a simple and efficient method to investigate ground characteristics along two transects on the ice-rich Schafberg rock glacier in the Eastern Swiss Alps. The results were compared with electrical resistivity tomography (ERT) and ground temperature data acquired simultaneously in boreholes. FDEM provides information on the electrical properties of the ground, allowing to investigate ground-ice distribution. Our device allowed measurements to a depth of around 7 m. In ice-rich permafrost, FDEM can provide an approximation of the active layer thickness, and ice-free zones within the permafrost such as intra-permafrost taliks can be identified. This rapidly applicable geophysical method can be used to monitor ground ice distribution easily and efficiently, making it an ideal complement to borehole temperature data, which only provide point information and are costly to install and maintain. At the Schafberg site the three methods FDEM, electrical resistivity tomography and borehole temperature measurements provided similar results, with regard to active layer thickness and the presence of unfrozen zones within the ice-rich permafrost.

An increasing number of studies highlight the controlling influence of water on rock glacier deformation velocities. The link between the concept of water‐driven shearing processes and numerous observations of correlating mean annual air or ground temperatures and rock glacier velocities is discussed here. We present a dataset measured at the Schafberg rock glacier in the Eastern Swiss Alps, complemented by temperature data from three other rock glaciers in the Swiss Alps, which allowed us to reconstruct the processes influencing both mean annual ground temperatures and rock glacier deformation velocity. Rock glacier hydrology is the parameter linking rock glacier temperature and velocities and is a crucial influencing factor. The main external forcing parameter appart from mean annual air temperature is early winter snow coverage. The study shows that the concept of water being a controlling factor for rock glacier velocity is no contradiction to the observed correlations between air or ground temperature and rock glacier deformation.

An alpine permafrost talus slope at Flüelapass (Eastern Swiss Alps) was observed using annual terrestrial laser scanning measurements between 2009 and 2018. The high-resolution digital elevation models derived from these measurements enabled the detection and quantification of mass wasting processes with an accuracy of a few centimeters. Rock fall, snow avalanche erosion, and debris flow tracks could be distinguished and their quantitative and qualitative contribution to talus slope growth and shaping was examined. Erosion rates were calculated for each of the investigated processes and an estimate for the recession rate of the talus slope head wall is reported. Currently, debris flows supply most of the debris inputs to the talus slope, while snow avalanches were found to play an important role in reshaping its surface morphology. Rock fall causes distinct grain size sorting down the slope, as the travel distance of rocks increase with their size. The presented data and results illustrate the current processes occurring at the talus slope surface, which appear to differ in quantity and quality from those during the onset of the talus slope formation.

Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock-slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0 × 10⁶ m³ failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2 km and removed over one million m³ of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30 s followed by ten debris flows within 9.5 h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near-immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche's runout path for Alpine hazard assessments.

Mountain permafrost is invisible, and mapping it is still a challenge. Available permafrost distribution maps often overestimate the permafrost extent and include large permafrost-free areas in their permafrost zonation. In addition, the representation of the lower belt of permafrost consisting of ice-rich features such as rock glaciers or ice-rich talus slopes can be challenging. These problems are caused by considerable differences in genesis and thermal characteristics between ice-poor permafrost, occurring for example in rock walls, and ice-rich permafrost. While ice-poor permafrost shows a strong correlation of ground temperature with elevation and potential incoming solar radiation, ice-rich ground does not show such a correlation. Instead, the distribution of ice-rich ground is controlled by gravitational processes such as the relocation of ground ice by permafrost creep or by ground ice genesis from avalanche deposits or glacierets covered with talus.
We therefore developed a mapping method which distinguishes between ice-poor and ice-rich permafrost and tested it for the entire Swiss Alps. For ice-poor ground we found a linear regression formula based on elevation and potential incoming solar radiation which predicts borehole ground temperatures at multiple depths with an accuracy higher than 0.6 ^∘C. The zone of ice-rich permafrost was defined by modelling the deposition zones of alpine mass wasting processes. This dual approach allows the cartographic representation of permafrost-free belts, which are bounded above and below by permafrost. This enables a high quality of permafrost modelling, as is shown by the validation of our map. The dominating influence of the two rather simple connected factors, elevation (as a proxy for mean annual air temperature) and solar radiation, on the distribution of ice-poor permafrost is significant for permafrost modelling in different climate conditions and regions. Indicating temperatures of ice-poor permafrost and distinguishing between ice-poor and ice-rich permafrost on a national permafrost map provides new information for users.

The interaction of glaciers and rock glaciers and the associated development and degradation of permafrost landforms are intensely discussed fields of periglacial geomorphology. This study presents examples of glacier–rock glacier interactions since the Little Ice Age in the Swiss and French Alps, based on sequences of current and historical maps and orthophotos as well as field observations. It is concluded from these examples that many creeping permafrost features, which were widely specified as 'glacier derived' in the literature, appear to be much older than the glacier itself and constitute the remains of rock glaciers, which were disrupted by glaciers. Furthermore, the environmental conditions causing an alternation of glaciers and rock glaciers at the same location are analysed here, and the processes leading to a transition from one landform to the other are identified in the examples given. The influence of climate change on rock glacier development appears to be ambiguous and partly contradictory. The examples show how rock glacier development can benefit from increased rock fall activity and deglaciation in warming periods.

Until today, snow depth data is mostly estimated based on point measurements, either collected manually or at automated weather stations. New photogrammetric technologies to map the snow depth distribution spatially continuous over larger areas are rapidly evolving. Especially in the field of unmanned aerial systems (UAS) new systems with better cameras and longer flight times are being developed. However, the specific strengths and weaknesses as well as the performance considering accuracy on homogeneous snow surfaces are not yet sufficiently investigated.

Therefore, we have simultaneously tested different photogrammetric platforms and sensors for snow depth mapping in the high alpine Dischma valley close to Davos (Switzerland) during winter season 2017/18. An extraordinarily snow rich winter challenged the data referencing approaches in particular. We acquired data over the whole Dischma valley with satellite and airplane based optical sensors. At two subsets in the Dischma valley, we flew with two different UAS and acquired ground-based data with a digital consumer camera. For the independent validation of the photogrammetric products we applied terrestrial laser scanning and measured snow depth by probing as well as by measurements on fixedly installed snow poles.

In this study we outline the experimental setup for a large campaign with different photogrammetric sensors and platforms. That will allow for an improved understanding of the specific advantages and disadvantages of different photogrammetric systems for operational, spatially continuous snow depth mapping in high alpine terrain over large areas.

An automatic method was developed to monitor rock glacier kinematics. Displacements derived from monoscopic time-lapse images were scaled and projected into the Swiss Coordinate System CH1903. We tested this method at the front of the rapidly creeping Ritigraben rock glacier, where time-lapse pictures of the rock glacier front were taken by an automatic camera with a temporal resolution of 3 h. The images were automatically processed using a Matlab algorithm. The output data were spatially resolved creep velocities between successive images and mean relative velocities over time. The digital elevation model used for the projection of the time-lapse data was acquired using terrestrial laser scanning (TLS). The resulting horizontal displacement velocities and accelerations were validated against GPS data measured at one point on the rock glacier front. The high temporal resolution of the time-lapse image velocities provided new insights on the kinematics of the rock glacier front, which could not have been discerned with the GPS or TLS measurements applied. The Ritigraben study site is particularly suitable for our approach due to the temporally constant movement directions. Snow coverage and fog are disturbing factors which can lead to failure of the method.

The paper presents an approach for the generation of digital elevation models (DEMs) of underwater areas from aerial images. Standard software-products do not provide the possibility to measure correctly through refractive interfaces, such as water. Existing solutions for that problem are based on oriented images and known water levels with the DEM points determined by forward intersection based on reconstructed image ray paths (ray tracing). In this article we present an integrated procedure for image orientation as well as DEM mass point determination from aerial imagery containing both land and underwater areas. The proof of concept was done by capturing UAV imagery of shallow water areas of a high-alpine lake in the Swiss alps. In the paper the processed dataset will be presented. Furthermore, the extraction and matching of image-points observed through water are discussed. The accuracy potential as well as practical limitations of processing multimedia-data are analysed.