Dr. Alexander Bast

Electrical resistivity tomography (ERT) is widely used to map, characterize, and monitor the ground in alpine and periglacial environments, where coarse blocky surfaces are often ubiquitous. ERT measurements typically use conventional steel electrodes in combination with a water-soaked sponge. However, ensuring an optimum contact resistance between the electrodes and the ground to obtain high-quality data is often challenging and requires considerable logistical, physical, and time commitment. To overcome this, we tested a promising sand-filled, fist-sized conductive textile electrode. We conducted ERT measurements using both steel and textile electrodes at a landslide and two rock glaciers in the European Alps with coarse blocky surfaces and performed statistical analyses to test the accuracy and precision of the proposed textile electrodes. Our results show that the textile electrodes can be used as an alternative to the conventional steel electrodes without limitations, as they ensure good galvanic contact with the ground and accurate resistivity measurements. The use of textile electrodes also resulted in lower contact resistances, less time invested, physical and logistical advantages, and reduced risk of injury. In the future, this will enable applications such as enhanced ERT monitoring and/or faster (quasi-3D) imaging of the interior of entire landforms.

According to various projections, climate change will alter the disposition for alpine mass movements, as well as their dynamics and the interaction of gravitational processes in process cascades. This will change the risks that people living in mountain regions are exposed to. The research program CCAMM - Climate Change Impacts on Alpine Mass Movements – initiated by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, fosters inter- and transdisciplinary research and thus addresses a socially relevant question and provides an important contribution to climate change adaptation of society. In this contribution, we provide an overview of the 22 projects and the envisioned outreach activities in 2025.

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.

Seismic refraction tomography is a commonly used technique to characterise rock glaciers, as the boundary between unfrozen and ice-bearing layers represents a strong impedance contrast. In several rock glaciers, we observed a reversed polarity of the waves refracted by an extended ice-bearing layer compared to direct-wave arrivals. This phase change may be related to the presence of a thin low-velocity layer (LVL), such as fine- to coarse-grained sediments, above a thicker ice-rich layer. Our results are confirmed by the modelling and analysis of synthetic seismograms to demonstrate that the presence of a low-velocity layer can produce a polarity reversal on the seismic gather.

Machine learning has grown in popularity in the past few years for susceptibility and hazard mapping tasks. Necessary steps for the generation of a susceptibility or hazard map are repeatedly implemented in new studies. We present a Random Forest classifier-based landslide susceptibility and hazard mapping framework to facilitate future mapping studies using machine learning. The framework, as a piece of software, follows the FAIR paradigm, and hence is set up as a transparent, reproducible and modularly extensible workflow. It contains pre-implemented steps from conceptualisation to map generation, such as the generation of input datasets. The framework can be applied to different areas of interest using different environmental features and is also flexible in terms of the desired scale and resolution of the final map. To demonstrate the functionality and validity of the framework, and to explore the challenges and limitations of Random Forest-based susceptibility and hazard mapping, we apply the framework to a test case. This test case conveys the influence of the training dataset on the generated susceptibility maps in terms of feature combination, influence of non-landslide instances and representativeness of the training data with respect to the area of interest. A comparison of the test case results with the literature shows that the framework works reliably. Furthermore, the results obtained in this study complement the findings of previous studies that demonstrate the sensitivity of the training process to the training data, particularly in terms of its representativeness.

The study of glacier rocks is of utmost importance in recent years due to the known changes in the structure of this kind of environment. A correct understanding of this structure can avoid severe problems related to natural hazards. Therefore, we propose integrating the use of multichannel analysis of surface waves (MASW) with those already widely carried out (such as ERT and EST). Through this study, there is the chance of obtaining shear wave velocity (Vs) profiles and thus revealing possible velocity inversions caused by the presence of the frozen layer.

In this study, a MASW has been carried out on data collected in the Swiss Alps over the past two years and the results show that the potential of this analysis for the characterization of mountain permafrost is promising.

Gebirgswälder bieten ein breites Spektrum an Waldleistungen, stehen aber aufgrund des globalen Wandels vor grossen Herausforderungen. Aufgrund zunehmender natürlicher Störungen sind gute lanungsgrundlagen zur Priorisierung der Bewirtschaftung von fichtendominierten Gebirgswäldern besonders wichtig. Dafür erstellen wir flächendeckende, interaktive Karten zur Waldstruktur und Störungsanfälligkeit der Wälder. Die Karten repräsentieren den aktuellen Waldzustand und weisen die Anfälligkeit der Schutzwälder gegen verschiedene Störungen aus. Kombiniert mit Informationen zur Schutzfunktion und Grundlagen bezüglich waldbaulicher und erntetechnischer Optimierung, dienen sie der Priorisierung von forstlichen Eingriffen in fichtendominierten Gebirgswäldern.

The degradation of mountain permafrost is well documented at many Alpine sites. Geophysical techniques have been intensively used to monitor these sites, since permafrost degradation is not only a proxy of climate change and global warming but also a possible source of slope instabilities and triggering of mass movements. While the use of non-invasive geophysical techniques is promising, the interpretation of different geophysical results can introduce ambiguities in defining the investigated subsoil and often does not lead to a quantitative estimation of the internal permafrost constituents (rock matrix, ice, liquid water and air contents). To overcome these limitations, we applied an optimized joint inversion approaches of electrical resistivity and refraction seismic tomography datasets collected at two Swiss rock glaciers (Schafberg - Canton Grisons, and Ritigraben - Canton Valais). Firstly, to improve the structural interpretation of the frozen near subsurface, we performed a structurally coupled cooperative joint inversion, optimizing the coupling parameters. Subsequently, we used the petrophysical joint inversion to quantify the composition of these mountain permafrost substrates, optimizing the numerical and petrophysical parameters. The obtained results agree with field observations and the borehole data collected at these two sites, opening new perspectives for the future quantitative monitoring of permafrost constituents.

A novel combination of borehole temperature, borehole piezometer and cross-borehole electrical resistivity tomography (ERT) data is used to investigate changing ice and/or water contents in the creeping ice-rich Schafberg rock glacier in the Eastern Swiss Alps. Instrumentation techniques and first results are presented. The rock glacier ice is close to its melting point, and the landform has locally heterogeneous stratigraphies, ice and/or water contents and temperature regimes. The measurement techniques presented continuously monitor temporal and spatial phase changes to a depth of 12gm and should provide the basis for a better understanding of accelerating rock glacier kinematics and future water availability.

Large landslides are known to generate powerful air blasts capable of causing damage far beyond the landslide runout. In many cases, observations of tree destruction are the only evi-dence to quantify the air blast danger. In this study, we proposed an approach to assess the air blast power using the tree breakage information, including the eigenfrequency prediction, tree motion calculation and breakage conditions. The tree is modelled as a flexible beam with elastic support at the tree base. Large tree deflection is accounted for when calculating the air blast loading and two failure modes (bending and overturning) are defined. Modelling results illustrated that tree eigenfrequency is always close to the air blast frequency, leading to a dynamic magnification for tree deformation. This magnification effect is greatly influen-tial in a weak air blast case, but the large tree inclination resulting from strong air blast load-ing would weaken the effect. Additionally, both failure modes are likely to occur and the exact failure mode of trees depends heavily on their bending and anchorage resistance. Therefore, further measurements need to be conducted on the biometric and mechanical characteristics of trees, which will improve the accuracy of air blast hazard assessment.

Windstorms are natural disturbances predicted to increase in frequency in the future, with a consequent increased risk of damage to forests. Such damage severely affects the forest structure and, therefore, its protection capacity. Previous studies analyzed post event conditions and the recovery time of abated forest within study areas smaller than 10 ha, while not accounting for larger spatial scales. In this study, we propose a new methodology to provide tools for the spatial assessment and monitoring of protection forests against snow avalanches affected by large-scale windstorms. Four indices have been used: (i) vegetation height model, (ii) surface roughness, (iii) stored volume height and (iv) adapted tree parameters, of which the latter two have been specifically developed for this goal. We selected and periodically recorded two windthrow areas using photogrammetric surveys (deriving dense point clouds) to assess the performance of the proposed indices and to investigate the long-term changes in protective effects (Disentis, CH) and the influence of snow cover (Franza, IT). Stored volume height and the adapted tree parameters were the best indices to capture the forest conditions and standing trees, respectively. The stored volume height was further used to estimate forest protective capacity in relation to the snow cover height. Analyzing the Disentis (CH) area, we concluded that the minimum level of protective capacity occurs ten years after the storm event. After 29 years, the forest protective capacity against natural hazards increased again as forest recovery proceeded. However, special attention should be given to gaps between growing trees that may be critical for potential avalanche formation as wood decays. This study provided new insights into the long-term protective efficiency of windthrow forests, introducing two new indices to spatially assess and monitors their evolution.

Steile Schutthänge mit einer fehlenden Vegetationsdecke sind in den Alpen allgegenwärtig und führen in Kombination mit Niederschlägen nicht selten zu Erosion und flachgründigen Rutschungen. Um die Gefahr durch diese Massenbewegungen zu reduzieren, wird durch ingenieurbiologische Massnahmen eine flächendeckende Oberflächenstabilität angestrebt. Insbesondere die ersten drei egetationsperioden sind für den Erfolg solcher Massnahmen ausschlaggebend. Um den Pflanzen möglichst gut unter die Arme greifen zu können, wird der Einsatz von Mykorrhizapilzen im ingenieurbiologischen Hangverbau innerhalb eines Feldexperimentes im Arieschtobel (Kanton Graubünden) getestet. Im Mai 2010 wurden dazu Heckenlagen mit einer kommerziellen Pilzmischung geimpft und mit herkömmlichen Heckenlagen ohne Impfung sowie einer Kontrollfläche verglichen. Die Impfung führte zu höheren Überlebensraten der eingebrachten Pflanzen, zu einer höheren Bodenaggregatstabilität, zu längeren und dickeren Wurzeln sowie einem tieferen und stärker differenzierten Wurzelraum. Die höhere ober- und unterirdische Biomasse führt nicht nur zu einer besseren Bodenstabilität, sondern reduziert zudem den Oberflächenabfluss und steigert die (Evapo-) Transpiration. Das vorgestellte Feldexperiment zeigt deutlich, dass die Zugabe eines kommerziellen, den ausgewählten Pflanzen angepassten Mykorrhiza-Inokulums sehr gewinnbringend im ingenieurbiologischen Hangverbau ist und, zumindest für den hier getesteten Anwendungsbereich, unbedingt berücksichtig werden sollte.

In order to prioritize protection forest management, it is essential to know where forests have an effect on avalanches and which criteria the forests have to meet to avoid avalanche releases and reduce avalanche runout distances. This contribution outlines how the current assessment of effective protection forest can be improved by combining process knowledge on forest-avalanche interactions with newly available remote sensing data, large-scale numerical modeling and cartographic visualization techniques. Within the scope of a practical application in the Canton of Grisons (Central Swiss Alps), we showcase how scenario-specific avalanche protection forest maps have been developed and implemented into natural hazard indication maps in collaboration with avalanche modelers and practitioners. We outline further developments of such combined information towards interactive, web-based decision support tools based on resulting maps of effective avalanche protection forests.

During recent decades, stable oxygen isotopes derived from tree-ring cellulose (δ¹⁸O_TRC) have been frequently utilised as the baseline for palaeoclimatic reconstructions. In this context, numerous studies take advantage of the high sensitivity of trees close to their ecological distribution limit (high elevation or high latitudes). However, this increases the chance that indirect climatic forces such as cold ground induced by permafrost can distort the climate-proxy relationship. In this study, a tree stand of sub-alpine larch trees (Larix decidua Mill.) located in an inner alpine dry valley (Val Bever), Switzerland, was analysed for its δ¹⁸O_TRC variations during the last 180 years. A total of eight L. decidua trees were analysed on an individual base, half of which are located on verified sporadic permafrost lenses approximately 500 m below the expected lower limit of discontinuous permafrost. The derived isotope time series are strongly dependent on variations in summer temperature, precipitation and large-scale circulation patterns (geopotential height fields). The results demonstrate that trees growing outside of the permafrost distribution provide a significantly stronger and more consistent climate-proxy relationship over time than permafrost-affected tree stands. The climate sensitivity of permafrost-affected trees is analogical to the permafrost-free tree stands (positive and negative correlations with temperature and precipitation, respectively) but attenuated partly leading to a complete loss of significance. In particular, decadal summer temperature variations are well reflected in δ¹⁸O_TRC from permafrost-free sites (r = 0.62, p < 0.01), while permafrost-affected sites demonstrate a full lack of this dependency (r = 0.30, p > 0.05). Since both tree stands are located just a few meters away from one another and are subject to the same climatic influences, discrepancies in the isotope time series can only be attributed to variations in the trees' source water that constraints the climatic fingerprints on δ¹⁸O_TRC. If the two individual time series are merged to one local mean chronology, the climatic sensitivity reflects an intermediate between the permafrost-free and –affected δ¹⁸O_TRC time series. It can be deduced, that a significant loss of information on past climate variations arises by simply averaging both tree stands without prior knowledge of differing subsurface conditions.

Under changing climate, temporal and spatial stability (stationarity) of growth responses of trees to weather and climate, which has often been presumed without explicit testing, is crucial for prediction of productivity and sustainability of forests. However, considering evolutionary adaptation of tree populations to wide spatiotemporal ecological gradients, extrapolation of linear responses, which could be observed in limited parts of the gradients (certain locality), can result in biased results. Accordingly, the plasticity of responses of tree-ring width of the eastern Baltic populations of Scots pine (Pinus sylvestris L.) to meteorological conditions across the regional climatic gradient was assessed using a mixed generalized additive model. The linear responses were assessed using a bootstrapped correlation analysis for comparison. The radial growth responses of the eastern Baltic population of Scots pine showed explicit regional gradients according to the local climates, indicating gradual shifts in the effects of winter temperature and summer moisture regime. Accordingly, temperature in late-winter and summer, as well as summer water deficit were identified as the main regional drivers of tree-ring width. Their effects were generally non-linear, indicating explicit spatiotemporal gradients in growth responses in the mid-part of species distribution. This also implied limited efficiency of simple linear models for the assessment of radial growth under moderate conditions. The responses to summer temperature indicated local optima, while the responses to drought index showed threshold values. The responses to winter temperature indicated positive effect of warming on growth. In some stands, specific non-stationary responses though were evident, suggesting that trees have adapted (specialized) to certain local climatic conditions, which are changing and thus explaining temporal shifts in growth responses. Nevertheless, the estimated responses suggested phenotypical adaptability limits of the eastern Baltic populations of Scots pine in a longer term, supporting the necessity of climate-smart management for sustainability of forest in the region in the future.

Temperature measurements in boreholes are the most common method allowing the quantitative and direct observation of permafrost evolution in the context of climate change. Existing boreholes and monitoring networks often emerged in a scientific context targeting different objectives and with different setups. A standardized, well-planned and robust instrumentation of boreholes for long-term operation is crucial to deliver comparable, high-quality data for scientific analyses and assessments. However, only a limited number of guidelines are available, particularly for mountain regions. In this paper, we discuss challenges and devise best practice recommendations for permafrost temperature measurements at single sites as well as in a network, based on two decades of experience gained in the framework of the Swiss Permafrost Monitoring Network PERMOS. These recommendations apply to permafrost observations in mountain regions, although many aspects also apply to polar lowlands. The main recommendations are (1) to thoroughly consider criteria for site selection based on the objective of the measurements as well as on preliminary studies and available data, (2) to define the sampling strategy during planification, (3) to engage experienced drilling teams who can cope with inhomogeneous and potentially unstable subsurface material, (4) to select standardized and robust instrumentation with high accuracy temperature sensors and excellent long-term stability when calibrated at 0°C, ideally with double sensors at key depths for validation and substitution of questionable data, (5) to apply standardized maintenance procedures allowing maximum comparability and minimum data processing, (6) to implement regular data control procedures, and (7) to ensure remote data access allowing for rapid trouble shooting and timely reporting. Data gaps can be avoided by timely planning of replacement boreholes. Recommendations for standardized procedures regarding data quality documentation, processing and final publication will follow later.

Gemäss verschiedenen Abschätzungen wird sich durch die Klimaveränderung nicht nur die Disposition für alpine Massenbewegungen, sondern auch deren Dynamik und die Interaktion von gravitativen Prozessen bzw. deren Verkettung in Prozesskaskaden verändern. Dies wird zu einem veränderten Risiko für die Schweizer Bevölkerung in Bezug auf alpine Massenbewegungen führen.
Das WSL Forschungsprogramm CCAMM - Climate Change Impacts on Alpine Mass Movements untersucht die Auswirkungen des Klimawandels auf alpine Massenbewegungen, um die daraus resultierenden Risiken besser abzuschätzen und geeignete Anpassungsstrategien für die Gesellschaft zu entwickeln. Im Folgenden stellen wir das WSL-Forschungsprogramm CCAMM vor.

Selon diverses estimations, le changement climatique modifiera non seulement la disposition des mouvements de masse alpins, mais aussi leur dynamique et l'interaction des processus gravitationnels ou leur enchaînement en cascade. Cela entraînera un changement de risque pour la population suisse par rapport aux mouvements de masse alpins.
Le programme de recherche du WSL CCAMM - Climate Change Impacts on Alpine Mass Movements - étudie les effets du changement climatique sur les mouvements de masse alpins afin de mieux évaluer les risques résultants et de développer des stratégies d'adaptation appropriées pour la société. Nous présentons ci-après le programme de recherche du WSL CCAMM.

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.

Pflanzen übernehmen wichtige Funktionen in der Bodenstabilisierung sowie zur Regulierung des Wasserhaushalts und erhöhen so auch die Wasserspeicherkapazität, welche für die Verhinderung flachgründiger Rutschungen entscheidend ist. Ein 3-Stufen-Filter und eine Multi Faktor Analyse mit Aspekten der Bodenmechanik, Vegetation und Topographie konnten von über 200 Rutschungen mehr als 90% erklären. Hinsichtlich der Verhinderung flachgründiger Rutschungen erhöht eine gute Waldstruktur nicht nur die Bodenstabilität, sondern beeinflusst auch den Bodenwasserhaushalt positiv. Diesbezüglich «optimale» Wälder weisen eine hohe 3D-Diversität auf: ober- und unterirdische Vielfalt an Arten, Alter, horizontaler und vertikaler Struktur sowie Durchwurzelung und Wurzelarchitektur in unterschiedlichen Sukzessions und Entwicklungsstufen.