Rock glaciers are typical landforms of mountain permafrost, composed of a surface of boulders and debris insulating an ice-bearing sediment layer, overlying a glacial till deposit and/or bedrock. It is well-known and documented that the degradation of mountain permafrost is influencing the triggering of slope mass movements (e.g. rock falls, debris flows, and floods), and the stability of infrastructures (e.g. ski resorts). Consequently, a reliable characterization of rock glacier’s structure is a key aspect for evaluating the risk related to their presence.

Since boreholes are challenging and expensive to realize in high mountain environments, geophysical methods are widely used to characterize the internal structure of rock glaciers. Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT) are among the most applied techniques to retrieve the electrical properties and the compressive wave velocities (Vp) in the subsurface.

In this work, we propose the application of the Multichannel Analysis of Surface Waves (MASW) to complement the information brought by ERT and SRT, and to overcome some limitations of the SRT method. For this purpose, the seismic data should be collected with low-frequency geophones (i.e., with 4.5 Hz natural frequency). The main advantage of the MASW approach is the possibility of obtaining shear wave velocity (Vs) profiles and to reveal velocity inversions in the subsurface, i.e., a lower velocity layer between two higher velocity layers (e.g., the unfrozen till deposit between the ice-bearing layer and bedrock). Furthermore, Vs are insensitive to the liquid phase in the medium, therefore MASW approach could be used to detect the ice-rich layer when it is surmounted by a water-saturated sediment layer (supra-permafrost flow), that could prevent P-waves from penetrating deeper.

In this work, we successfully tested the MASW method at the Flüela rock glacier (Engadine, Switzerland). ERT results clearly suggest the presence of an ice-rich layer, but the SRT analysis surprisingly does not show P-wave velocities consistent with this interpretation. The Vp model reveals in fact the typical values of liquid water. On the other hand, the Vs profiles retrieved from the MASW approach are in very good agreement with the ERT outcomes. Therefore, we hypothesise the presence of a thin water-saturated sediment layer on the top of the ice-rich layer, that would prevent P-waves penetration. In order to support our hypothesis, we performed a seismic full-wave forward modelling: the synthetic shot gathers are consistent with the real ones, both in terms of surface wave dispersion and P-wave first-arrival times.

How to cite: Pavoni, M., Barone, I., Boaga, J., Gaona Torres, S. J., and Bast, A.: Advantages of applying the Multichannel Analysis of Surface Waves (MASW) in ice-rich rock glacier environments: A case study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8864, https://doi.org/10.5194/egusphere-egu25-8864, 2025.

In recent years, the rockslide near Spitze Stei (Kandersteg, Switzerland) has shown elevated displacement rates exceeding 10 cm per day, indicating a growing instability of 20 million m³. This increased activity triggers frequent mass movements, including rockfalls, gravel flows, and debris avalanches, which elevates the potential for major events with secondary consequences such as debris flows and flooding.

To mitigate the risks associated with the Spitze Stei rockslide, extensive monitoring has been in place since 2018, including borehole measurements of temperature and water pressure and surface displacement observations. These measurements underline the presence of degrading permafrost and planes of enhanced gliding and shear deformation. However, the limited spatial coverage of these methods makes it challenging to understand slope-wide subsurface processes, which are crucial for characterizing instability and identifying mass movement triggers, especially in complex, highly active rockslides with multiple rock compartments.

Our study addresses these challenges through a passive seismic experiment to quantify mass movement activity and investigate subsurface processes at Spitze Stei. In this talk, I will discuss the two main research questions that motivate our study:

• Are there correlations between meteorological factors and rock slope stability that reflect climate-induced changes? How can they be quantified?
• Can seismology constrain subsurface processes, such as freeze-thaw cycles, water pressure variations, and progressive damage that affect rock slop stablitity? How these processes impact the dynamics of the rock slope?

To address these questions at the Spitze Stei rockslide, we develop a machine learning approach combining seismic and infrasound data to monitor rock falls, avalanches, and possibly stick-slip tremors reflecting frictional sliding within the slope. Furthermore, we use interferometric seismic noise analysis to detect small changes in elastic properties within the rock slope, which may be related to stability changes and permafrost degradation.

The rich ancillary data acquired at Spitze Stei offers a unique opportunity to validate our seismic methods against independent measurements and refine the interpretation of our results. Such analysis enhances warning efforts, deepens our understanding of triggering factors and their thresholds, and establishes a foundation for continuous seismic monitoring of rockslide dynamics in the context of climate change.

How to cite: Chmiel, M., Walter, F., Husmann, L., Belli, G., Hibert, C., Hählen, N., and Kienholz, C.: Multi-instrumental insights into the dynamics of an active rockslide near Spitze Stei, Switzerland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13168, https://doi.org/10.5194/egusphere-egu25-13168, 2025.

Recent years have shown the destructive nature associated with debris flows in alpine regions, including densely inhabited regions in Central Europe. Surge fronts within debris flows increase peak discharge and the dynamical complexity, which contributes much to the hazard potential. In recent years, numerical models helped to gain insights into the surging behavior of debris flows, in particular into the formation of surging waves including roll waves and erosion-deposition waves (Edwards & Gray, 2014). In order to capture the dynamic processes involved in the formation and propagation of flow surges, it is necessary to obtain distributed observations in the spatio-temporal domain. However, demanding field installations have confined studies to theoretical or laboratory settings, and results have yet to be validated under large-scale, real-world conditions. In this study, we close this gap by utilizing distributed, near-torrent seismic measurements at the Illgraben debris flow observatory maintained by the Swiss Federal Institute of Forest, Snow and Landscape Research WSL.

In 2024, a chain of 33 seismic nodes was deployed along a 2-kilometer section of the Illgraben torrent, with a spacing of 70 m between each node. In total, 10 debris flows with front velocities varying between 0.2 and 6 m/s and maximum flow heights varying between 1 - 3 m were recorded. The nodal array detected debris flow signals up to 2 km away, at a stage when the flows were still mobilizing in Illgraben’s upper catchment. The seismic record is characterized by high-frequency signals commonly attributed to particle-ground impacts within the debris flow. Additionally, it is found that steps in torrent geometry (check dams) produce a strong, low-frequency (1 – 10 Hz) background signal that is detectable kilometers away from the torrent.

Our measurements provide novel data of the spatio-temporal evolution of debris flows: Bifurcations of surge fronts and spawning of erosion-deposition waves can be observed and traced along the torrent. The data furthermore reveal the interaction between surging waves and the debris flow front. Our dense seismic recordings thus show how and where surging waves develop and how they modify maximum discharge and thus allow inferring the debris flows destructive potential.

The distributed seismic measurements at Illgraben offer new perspectives on measuring flow instabilities such as surge fronts and roll waves, allowing us to track them along extended torrent sections. They furthermore enabled us to refine our understanding of the seismogenesis of torrential processes, which is often only investigated with single stations or sparse networks. In a next step we plan to use these findings to better represent pulsing behavior in numerical debris flow models.  

Edwards & Gray, 2014, J. Fluid Mech., doi:10.1017/jfm.2014.643

How to cite: Wetter, C., Walter, F., McArdell, B., Zhang, Z., Aichele, J., and Fichtner, A.: Distributed Seismic Sensing of Debris Flow Dynamics at Illgraben, Switzerland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8772, https://doi.org/10.5194/egusphere-egu25-8772, 2025.

In the Mont-Blanc massif (western European Alps), seismic stations record numerous signals originating from surface mass movements, such as rockslides, rockfalls, and serac avalanches. The large number of recorded signals makes the automation of the processing workflow essential for practical application. These seismic waveforms differ significantly from those generated by earthquakes, making standard algorithms unsuitable for their analysis. The signals typically exhibit an emergent onset, making it challenging to precisely determine their start time. Moreover, the arrival times of P and S waves, routinely used for earthquake localization, cannot be easily identified. The seismic records also vary in length, reflecting the differing durations of the associated phenomena.

To analyze such data using a seismic network, we adapted selected algorithms to address these challenges. For detection, we chose the STA/LTA algorithm, and for localization, we used amplitude decay algorithm and BackTrackBB software, which exploits wave field coherence. To test these algorithms, we created a reference dataset consisting of large, well-documented mass movements. The dataset was developed using regional mass movement databases, webcam image analysis, direct observations made by a network of observers, and seismic data from the Sismalp network. This reference dataset enabled us to fine-tune the algorithms and automate the processing of waveforms related to mass movements.

How to cite: Kokowski, J., Helmstetter, A., Larose, E., Ravanel, L., and Cailhol, X.: Using a seismic network for automatic detection, localization and characterization of mass movements in the Mont-Blanc massif , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9189, https://doi.org/10.5194/egusphere-egu25-9189, 2025.

Snow avalanches pose a significant hazard in mountainous areas, especially when snowpacks block roads, either burying vehicles directly or exposing traffic to subsequent avalanches during active cycles.

We have been monitoring avalanche activity along road stretches in Northern Norway since 2022 using Distributed Acoustic Sensing (DAS),  a technology capable of theoretically covering spans of up to 170 km. Traditional detection methods often focus on only a limited section of a road stretch, making effective risk management challenging. DAS powered alert system can work unaffected by visual barriers and in adverse weather conditions. The developed algorithm identifies avalanches affecting the road and estimates accumulated snow. Moreover, the system can also detect vehicles on the road, offering invaluable support to search and rescue operations.

Over 3 winters the system successfully identified 10 road-impacting avalanches (100% detection rate). Our results via DAS align with the previous works and indicate that low frequency part of the signal (<20 Hz) is crucial for detection and size estimation of avalanche events. We have identified subsets of snow avalanches based on the paths they followed and discuss the snow accumulation and deposition signatures on signals. Various fiber installation methods are explored to optimize sensitivity in detecting avalanches. The findings highlight the system’s robustness and low maintenance demands, offering a clear advantage over conventional systems, which are costly to install, have restricted coverage, or are vulnerable to environmental factors such as weather and lighting.

How to cite: Turquet, A., Svendsen, G. K., Wuestefeld, A., Nyhammer, F. K., Nilsen, E., Persson, A., and Refsum, V.: Insights from Snow Avalanche Detection in Norway: A Distributed Acoustic Sensing (DAS) Study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6219, https://doi.org/10.5194/egusphere-egu25-6219, 2025.

Landslides are complex systems, which are commonly investigated using data from punctual sensors, e.g., installed in boreholes. Assuming lateral variations in the subsurface fabric by interpolating the data from sparse boreholes may provide biased insight into the processes and architecture of landslides. Geophysical methods can be used to overcome this issue, gaining information about the physical properties (e.g., electrical conductivity, seismic velocity) of the subsurface covering large areas with high resolution. In landslides, geophysical methods have been used to investigate the geometry of the geological units and the depth to the bedrock, of the position of sliding planes and to compute the volume of mobilized material. Moreover, recent studies have demonstrated the ability of geophysical methods to quantify variations in the hydrogeological properties in an imaging framework. While the use of borehole data helps to reduce ambiguities in the interpretation of the geophysical images, the combination of more of different geophysical methods allows to enhance the coverage and resolution of the investigation as well as to reduce modeling uncertainties.

In this contribution, we present the combination of electrical and electromagnetic methods for the hydrogeological characterization of a clay-rich landslide located in Upper Austria (Austria). The investigation considers a two-step approach: (1) mapping at the large scale using electromagnetic methods at low induction number, and (2) selection of particular areas for the conduction of spectral induced polarization (SIP) transects. The first step aims resolving the main variations of clay content as well as to identify preferential flow paths for near-surface run-off; while in the second step SIP measurements are used to quantify hydraulic conductivity and water content. EMI mapping was conducted using vertical and horizontal configurations with two different instruments, each one consisting of three receivers, resulting in mapping information along 12 different geometries reaching a maximal nominal depth of investigation of 7 m. SIP measurements were collected at 12 different frequencies in the range between 0.25 and 225 Hz using 64 electrodes in each transect, with a spacing of 2.5 m to reach a depth of investigation of ca. 50 m.

Maps of the electrical conductivity gained by EMI measurements reveal strong lateral variations in clay content across the entire site. The inversion of the SIP data permits to quantify vertical and lateral changes in the hydraulic conductivity and water content along the transects. Our results demonstrate that an adequate processing of the data and the use of cascade inversion of multi-frequency SIP data permit to resolve for consistent hydraulic properties using different petrophysical approaches. Inversion of the EMI data along the SIP profiles reveals consistent results in the variations of electrical conductivity, permitting to validate the SIP results in shallow areas. Additionally, we investigate the relationship between electrical and hydraulic conductivity along the SIP transects and use it for a quantitative interpretation of the EMI maps; thus, permitting a hydrogeological investigation of the entire study area.  Our results reveal the potential of combining EMI and SIP for quantitative investigations of landslides.

How to cite: Flores Orozco, A., Hettegger, A., and Moser, C.: Hydrogeophysical investigation of clay-rich landslides through combined electrical and electromagnetic methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11136, https://doi.org/10.5194/egusphere-egu25-11136, 2025.

The last weeks of June 2024 were a very active period in the Alps with various floods, landslides, rockfalls and debris flows. In particular, the Mattertal valley (Switzerland) was hit by intense rainfall on June 20-22, following a very snowy winter and rainy spring. This led to various floods and debris flows, including the cutting off of the road and railway to the famous town of Zermatt. Also, some exceptional slope destabilization were also observed before the late June storm activity. Forecasting such natural hazards and anticipating the effects of rapid erosion processes is key for public managers, especially for energy and communications infrastructures and tourist resorts in mountainous valleys.

Using passive seismic sensors placed on the Gugla rock glacier (2700 m a.s.l) above Herbriggen village, Mattertal, we have detected landslides and quakes around the rock glacier almost continuously from 2016 to 2024 [1]. Using the same seismic instrument, we were also able to measure relative seismic velocity changes on a daily basis, which are indicative for the variations in stiffness at depth undergone by the rock glacier [1]. We observe seasonal variations of relative velocity changes and rockfall activity, mainly controlled by the freeze-thawing cycles. Melting seasons and wet summer episodes (storms) generally lead to seismic velocity drops of 2-3% in May-June. In June 2024, however, we observed a significant decrease in seismic velocity (-6.5%), which corresponds to a significant decrease in stiffness (ice melting) and a high liquid water content (snow melting infiltration), both lowering ground stability. This reduction in ground stability is likely to be responsible for the observed faster kinematics of the frontal part of the rock glacier, as well as rockfall and debris flow activity increase downstream.

Since this reduction in ground stability is likely to have occurred further in the Mattertal catchment at the same elevation and orientation, our work emphasizes that this reduction in seismic velocity at the catchment scale may be a good proxy for the higher sensitivity of the catchment to environmental triggers such as rainfall, eventually leading to a higher probability of slope destabilization.

[1] A. Guillemot, et al: Seismic monitoring in the Gugla rock glacier (Switzerland) : ambient noise correlation, microseismicity and modelling, Geophys. J. Int. 221, 1719-1735 (2020).

This work was partially funded by the Wallis canton, and by the European Research Council (ERC) under grant No. 101142154 - Crack The Rock project.

How to cite: Larose, E., Strapazzon, M., Guillemot, A., Helmsetter, A., and Favre-Bulle, G.: The June 2024 Mattertal slope destabilizations: zoom into the Gugla rock glacier, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6320, https://doi.org/10.5194/egusphere-egu25-6320, 2025.

The extreme Ahr flood 2021 caused 135 fatalities (and one still missing), severe damage and enormous geomorphological changes of the riverbanks, floodplains and adjacent slopes. Many slopes were undercut and several landslides have been reactivated. The Müsch landslide is located in a narrow section of the upper Ahr valley. The instability is 100 m wide, 200 m long, and of unknown age. Approximately 7000 m³ of the landslide toe were eroded by the 2021 flood. After the flood, the landslide was reactivated, resulting in minor changes on the surface (e.g. opening of cracks). A major reactivation of the entire landslide body, however, might potentially lead to a landslide dammed lake inundating buildings upstream. Thus, there is the need to better understand the landslide structure and behavior.

Since water saturation plays a crucial role in landslide activities, an electrical resistivity tomography (ERT) moisture monitoring system has been set up in January 2024 along one longitudinal and one cross profile (both 200m). We use permanently installed steel electrodes with a spacing of 2.5 m for both profiles. Monthly repeated manual ERT measurements (array: gradient) are analyzed with time-lapse inversions.

ERT results show an increasing reduction in resistivity values until June 2024 down to about 10-15 m along both ERT profiles correlating with increasing water saturation in the landslide body. The opening and widening of cracks indicate accelerating landslide activity from April onwards and continuing until July 2024 when the topsoil had started to dry out while the deeper layers were still sufficiently wet. Subsequently, landslide activity slowed down. This is in line with precipitation records and modelled soil moisture distribution over 2 m soil profiles by the German Weather Forecast (DWD) and observations made in 2023, in which similar dynamics occurred.

Continued measurements and analyses will enable us to better assess water saturation of the landslide and its spatial heterogeneity. Results will be correlated to rainfall data, on site measured soil moisture data (10 and 40 cm depth) as well as data of a passive seismic monitoring of the landslide, which is in place since October 2021. Deep drillings are scheduled for early 2025, with inclinometers and piezometers subsequently installed on behalf of the State Geological Survey. A combination of those measurements will help to better understand landslide behavior and assess potential hazards and risks.

How to cite: Bell, R., Schoch-Baumann, A., Dietze, M., and Schrott, L.: Electrical Resistivity Tomography (ERT) Moisture Monitoring on the Müsch Landslide (Ahr valley, Germany), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17256, https://doi.org/10.5194/egusphere-egu25-17256, 2025.

This study proposes an integrated methodology to investigate hydrogeological instability, combining remote sensing with in-situ geophysical surveys in Gorgoglione, a small town in Basilicata, southern Italy, located in a low mountain area (~800 m a.s.l.). The Italian Apennines, where Gorgoglione is situated, are highly susceptible to geomorphological instability due to the interplay of lithology, relief morphology, active tectonics, seismicity, climate, and vegetation. In recent decades, land abandonment around small towns and villages has exacerbated soil erosion and increased landslide occurrence. These challenges are further compounded by inadequate urban planning, poor construction practices, and ineffective water and wastewater management, along with a lack of sufficient landslide mitigation measures. Unlike regions experiencing rapid urbanization, these areas face issues tied to unregulated urban decline, making them critical test beds for developing innovative methods to study and mitigate natural processes that heighten urban risks.

The research aims to provide insights into residual landslide risks to support the development of effective mitigation and management strategies. The activity of instability processes was analyzed using SAR interferometry from both satellite and ground-based platforms. Subsurface geological and lithostratigraphic characteristics were reconstructed by integrating geological and geomorphological information with geophysical techniques, including Electrical Resistivity Tomography (ERT) and Horizontal-to-Vertical Spectral Ratio (HVSR) analysis of ambient seismic noise. The pronounced directional patterns observed in HVSR analysis are being investigated to determine their potential correlation with the landslide movement direction identified through SAR interferometric data.

How to cite: Calamita, G., Perrone, A., Falabella, F., Pepe, A., Stabile, T. A., Gallipoli, M. R., Serlenga, V., Gueguen, E., Bellanova, J., Bentivenga, M., and Piscitelli, S.: Integrating Remote Sensing and Geophysics to Assess Landslide Risk in the Italian Apennines: A Case Study in Gorgoglione, Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6485, https://doi.org/10.5194/egusphere-egu25-6485, 2025.

The Pays de Herve, located in the eastern part of Belgium, can be characterized as a multiple sections tableland with gentle slopes of less than 15°. It is located in the vicinity of the northern section of the Hockai Fault Zone, a 42 km-long seismogenic fault zone, that is characterized by the presence of fault scarps, multiple dissection elements and the presence of more than 20 paleo-landslides. Among these latter, the Manaihan landslide is the most studied and monitored landslide in the area. From a geological point of view, it developed in a Upper Cretaceous sedimentary setting, i.e., Vaals Clays overlaying Aachen sands. Even today, the slope is affected by instability and subsidence phenomena, likely linked to anthropogenic loading combined with prolonged periods of rainfall and possibly historic seismic events leading to liquefaction in the Aachen sands.

Recently, new geophysical surveys have been carried out using an integrated approach, combining electrical resistivity measurements, active seismic methods (interpreted as P-wave tomography and MASW), and passive seismic techniques (single-station H/V). The key question to address is: How deep is the sliding surface, and is it possible to identify it?

The combination of these surveys allowed the identification of two main layers. The first layer has a variable thickness ranging between 5 m and 20 m. On the electrical resistivity tomography, it corresponds to a more conductive layer with values between 5 and 20 Ωm, and on the seismic tomography, it shows velocities between 500 and 1300 m/s. From the electrical and seismic tomographies, the second layer appears to be more resistive, with values ranging between 30 and 50 Ωm, and P-wave velocities exceed 1500 m/s. Based on the geological map and their physical properties, the identified layers have been attributed to the Vaals clay formation and the Aachen sands, respectively.

The H/V measurements were processed to produce sections showing the variation of H/V amplitude (or the log of H/V) with depth. If multiple H/V measurements can be aligned in a linear array and the surface layer can be assumed to be homogeneous, i.e., shear wave velocity increasing with depth, the H/V curves along the alignment can be modeled together to create a 2D section. Several H/V sections could be developed for the Manaihan landslide, revealing a similar pattern of contrasts between the before mentioned layers. The main contrast is located at a depth ranging from 15 m to 40 m and corresponds to the interfaces identified by ERT and SRT. This interface is present beyond the landslide and even outside of it, suggesting that it may be associated to the geological contact between the Vaals clays and the Aachen sands. The conductive layer identified in the ERTs can furthermore be associated to very low log H/V amplitudes in the upper range of the H/V sections until 10-20 m depth. The H/V amplitude analysis of all the identified sections suggests that the sliding surface of the Manaihan landslide is located at the contact between the clay and the sand layers.

How to cite: Pazzi, V., Innocenti, A., Mreyen, A.-S., Cauchie, L., Caterina, D., Hussain, Y., Dorival, V., and Havenith, H.-B.: Seismic noise measurements for the characterisation of Pays de Herve landslides, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17452, https://doi.org/10.5194/egusphere-egu25-17452, 2025.