The Ticino Canton, located in the Swiss Alps, is characterized by steep valleys with important slope instabilities. It particularly affected by rock avalanches and landslides especially after important precipitations.
One of those is the Cima del Simano gneissic mountain in the Blenio valley. The top, reaching an altitude of 2550m, is strongly weathered and presents one main 500 meters-long open fracture and several smaller fractures. Some preliminary satellite InSAR results highlight downward movements. This instability is worthy to be studied since it represents a risk for the road passing at the bottom or villages implanted on its slopes. 
Nevertheless, this mountain is challenging to study because of (1) its bad accessibility: the top without access roads is covered by snow half of the year and (2) the atmospheric effects: the top is often hidden by clouds.  
For those reasons, the study is carried by combining several remote sensing techniques to acquire a maximal amount of information on the instability movements such as rockfalls, topplings and slow deep-seated landslides. Those techniques are extensometers, GNSS, Lidar, satellite InSAR, Ground-Based InSAR (GB-InSAR) and drones Structure from Motion (SfM). They are aimed at confirming the failure scenarios, predicted based on field observations and by structural analyses.  
With Lidar and SfM point clouds one is able to detect small blocks in toppling or sliding, which are confirmed by the results of GNSS and GB-InSAR campaigns, as well as zones of accumulations of rock avalanches debris. By means of GB-InSAR and satellite InSAR one can detect more long-term moving areas (few mm/year). We estimate the limits of those instabilities and their corresponding volume with structural analyses of the discontinuities using Coltop3D and by applying the Slope Local Base Level (SLBL) method. 
For the main fracture, we try to delimit the contours of the instability, but such an aperture and hypothetical instability edges are hardly explained by the actual topography. One explanation is that this fracture was inherited from an older important gravitational event, whose involved material collapsed and was washed out since the event occurred.

How to cite: Wolff, C., Choanji, T., Fei, L., Gutierrez, A., Derron, M.-H., Jaboyedoff, M., Pedrazzini, A., and Rivolta, C.: Use of combined monitoring remote sensing techniques for the study of active fractures in a remote area: Case of Cima Del Simano rockslide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13466, https://doi.org/10.5194/egusphere-egu23-13466, 2023.

Global atmospheric warming and associated deglaciation effects lead to the increasing development of slope instabilities in glacier forefield environments. The primary drivers are debuttressing effects due to retreating glaciers, exposure of previously contained rock masses and thawing of permafrost. Such effects can lead to a decrease in slope stability and possible resulting failure in the generally rough and steep terrain encountered in high mountains, such as the densely populated European Alps, calling for extensive hazard analyses of such features.

Within the framework of the ESA Regional Initiatives for the Alps, the AlpGlacier project analyses capabilities to monitor glaciers in the Alps from the Copernicus Sentinel satellites. The derived products are: (a) snow cover and (b) flow velocities, both on glaciers, as well as (c) pro-glacial lakes and (d) slope instabilities, both in glacier forefields. Synergies through a combination of sensors, with focus on Sentinel-1 and -2, are tested and sensor limits identified. The presented work focusses on the slope instability product. The specific challenges to detect slope instabilities are the highly variable rates of movement combined with the long-lasting presence of snow cover, requiring the application of diverse DInSAR processing approaches and a detailed visual analysis of the observed changes. We present a comparison of standard and advanced DInSAR methods using Sentinel-1 data to evaluate the possibilities and limitations to detect slope displacements in three selected study regions in the European Alps. The Mattertal region in Switzerland, Mont Blanc region in France/Italy and Ötztal Alps in Austria are characterised by steep relief, the occurrence of permafrost, dense infrastructure and known slope instabilities. All sites experience glacier retreat since the Little Ice Age that leads to the potential formation of glacier lakes and slope instabilities. Continuous Sentinel-1 acquisitions exist for each site, which are used in multiple DInSAR techniques to detect and map slope instabilities, allowing an assessment of the variability of detected surface motion and suitability of the applied methods.

Results show a widespread distribution of slope instabilities moving at <2 cm/year to >30cm/year. Movements include soil and rock slides, rock falls, rock slope deformations as well as permafrost-related movements and rockglaciers. Time series extracted for exemplary movements occurring along retreating glaciers in each study region show distinct accelerations in the last 5 years that may be related to deglaciation effects. The results are validated with optical and SAR offset tracking methods.

How to cite: Jones, N., Strozzi, T., and Paul, F.: Slope instability mapping in glacier forefield environments of the Alps using standard and advanced DInSAR techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15632, https://doi.org/10.5194/egusphere-egu23-15632, 2023.

Spaceborne synthetic aperture radar interferometry (InSAR) is commonly applied in mountain environments to detect and monitor mass movements to support local or regional natural hazard evaluation. InSAR technology is being increasingly used thanks to the recent open data policies or relatively low costs. Despite the remarkable advantage of observing wide regions, the technology presents intrinsic limitations which are emphasized or reduced depending on the satellite and the characteristics of the area investigated. Satellites with different revisiting times and operating in various bands, namely in the X (wavelength lambda = 3.1 cm), C (lambda of 5.6 cm), and L (lambda of 23.1 cm) bands, are suitable for observing mass movements with different characteristics depending on mountain relief, vegetation, and displacement rates. However, the use of a certain satellite can result in misleading displacement rates or a lack of measurements.

In this work, we compare the data from different satellites to highlight the capabilities and the general limitations of the method for application in a 1’500 km² wide area of the Southern Swiss Alps, covering the Canton Ticino and a portion of Canton Grisons. The main valleys have a north-south orientation, characterized by steep slopes of altitudes between 2’000 and 3’000 meters a.s.l., covered by typical alpine vegetation. The dataset processed includes the ERS, Envisat, Sentinel-1, and RadarSAT missions, both ascending and descending geometries for a time frame of several decades. The distribution of the instabilities of the whole region is provided by the update “Catalog of the instabilities of Canton Ticino, 2016” expanded to the adjacent Calanca and Mesolcina valleys of Canton Grisons. The mapping has been made by the Institute of Earth Sciences of the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) in the framework of the Interreg AMALPI 18 project and the mapping of the geological maps Osogna, Grono, Biasca, and Mesolcina of the Swiss Geological Atlas AG25. We validate the InSAR results by comparing the surface velocities with terrestrial monitoring, field observations, and historical information that describe the rock slope failure activity.

From the statistical information obtained by the comparison of slope displacements detected through the Permanent Scatterers technique PS, the areas affected by instability, and different movement rates, we make considerations on the use of the PS for monitoring rock slope failures of different types and rates of displacement in a mountain context.

How to cite: De Pedrini, A., Ambrosi, C., Manconi, A., and Agliardi, F.: Evaluation of rock slope failure activity by comparison of multi-sensor InSAR datasets in the Sothern Swiss Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15433, https://doi.org/10.5194/egusphere-egu23-15433, 2023.

The interaction between glacier retreat and rock slopes has gained considerable attention in the past years due to climate change. Glaciers shape mountain slopes and can daylight zones of weakness as they recede. Glaciers can act as a preparatory factor or trigger for slope failure. A retreating glacier at the slope's toe is often cited as the cause of failure. However, the relationship between glacier retreat and rock-slope stability is much more complicated, particularly for landslides that lack an explicit trigger. We studied a paraglacial slope failure at Grewingk Lake and Glacier in southcentral Alaska, United States. The collapse occurred on October 14, 1967, with no specific trigger, such as heavy rain or seismic activity on the day of the event. Grewingk Glacier is a lake-terminating glacier that has experienced and continues to experience rapid retreat, as have most glaciers around the world. The rapid retreat and the location of the glacier at the time of the collapse could lead to the conclusion that this was the cause of the collapse. However, a thorough examination of the structural geology of the slope and processes that could contribute to reduce the slope stability showed that the retreat of the glacier is only part of the tale. The structural preconditioning, together with an accumulation of seismic activity and daylighting fracture planes progressively contributed to the slope's destabilization. Our study emphasizes the value of examining the temporal trends of paraglacial rock-slope failures in situations in which there was no evident trigger at the time of the collapse.

How to cite: Lemaire, E., Dufresne, A., Hamdi, P., Higman, B., and Amann, F.: Evaluation of factors that led to the 1967 paraglacial slope failure at Grewingk Lake and Glacier, Alaska, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12711, https://doi.org/10.5194/egusphere-egu23-12711, 2023.

The Kandersteg region, Switzerland, has a history of catastrophic rock slope failures that repeatedly occurred throughout the Holocene, with volumes reaching hundreds of millions of cubic meters. In recent years, the rock slope near "Spitze Stei" has exhibited elevated displacement rates exceeding 10 cm per day, suggesting a growing instability of up to 20 million m³.

Due to the destructive potential of the Spitze Stei rockslide, extensive monitoring has been put in place since 2018, including borehole temperature logging, water pressure measurements and surface displacement monitoring. Borehole temperature measurements and direct observations highlight the presence of degrading permafrost, possibly on planes of enhanced gliding and shear deformation. However, point-like borehole measurements and sensing technology focusing on the slope surface cannot fully describe processes influencing slope dynamics, such as freeze-thaw cycles, varying water pressure, and progressive damage within the slope. These processes have lateral and depth-dependent sensitivity, causing changes in the rock's elastic properties, thus impacting seismic velocities. Here, we aim to provide a better understanding of these primary processes driving the dynamics of Spitze Stei. To this end, we analyze variations in relative seismic velocities (dv/v) measured through continuous seismic data and seismic interferometry. With this technique we transform seismic noise into coherent signals through cross-correlations of data from five 3-component seismometers.

The initial results of the time series of relative seismic velocity variations (dv/v) constrain the lateral and depth-dependent extent of subsurface changes. The results indicate that a substantial decrease in relative seismic velocity occurs at the times of rather heavy rain (rainfall >10 mm d^-1). This suggests that dv/v reflects material changes caused by pore pressure increase and reduction in material strength. The shallowest dv/v measurements agree with surface displacements displaying cyclic slipping of material.

We discuss how our observations help identify the primary processes controlling the dynamics of the Spitze Stei rockslide, give quantitative insight into rock damage, and allow separating effects from irreversible damage growth and reversible thermoelastic and hydrologic variations. This knowledge is needed to better understand the development of large rock failures and potentially improve warning systems.

How to cite: Chmiel, M., Walter, F., Husmann, L., Gassner, J., and Kienholz, C.: Towards a better understanding of large-scale rock slope dynamics with seismic interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11642, https://doi.org/10.5194/egusphere-egu23-11642, 2023.

During the RESOLVE project ("High-resolution imaging in subsurface geophysics: development of a multi-instrument platform for interdisciplinary research"), continuous surface displacement and seismic array observations were obtained on Glacier d'Argentière in the French Alps for 35 days during May in 2018. This unique data set offers the chance to perform a detailed, local study of targeted processes within the highly dynamic cryospheric environment. In particular, the physical processes controlling glacial basal motion are poorly understood and remain challenging to observe directly. Especially in the Alpine region for temperate based glaciers where the ice rapidly responds to changing climatic conditions and thus, processes are strongly intermittent in time and heterogeneous in space. Spatially dense seismic and GPS measurements are analyzed with machine learning techniques to gain insight into the underlying processes controlling glacial motions of Glacier d'Argentière.

Using multiple bandpass-filtered copies of the continuous seismic waveforms, we compute energy-based features, develop a matched field beamforming catalogue and include meteorological observations.Features describing the data are analyzed with a gradient boosting decision tree model to directly estimate the GPS displacements from the seismic records.

We posit that features of the seismic noise provide direct access to the dominant parameters that drive displacement on the highly variable and unsteady surface of the glacier. The machine learning model infers daily fluctuations as well as longer term trends and the results show on-ice displacement rates are strongly modulated by activity at the base of the glacier. The techniques presented provide a new approach to study glacial basal sliding and discover its full complexity.

How to cite: Umlauft, J., Johnson, C. W., Roux, P., Trugman, D. T., Lecointre, A., Walpersdorf, A., Nanni, U., Gimbert, F., Rouet-Leduc, B., Hulbert, C., and Johnson, P. A.: Mapping glacier basal sliding applying machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7888, https://doi.org/10.5194/egusphere-egu23-7888, 2023.

Landslide dams are counted as one of the most destructive mountain hazards. They pose flood hazards downstream and damming effects upstream. Assessing their stability requires either a detailed case study or relying on geomorphic indices. A case-study project, while being accurate, is time-consuming and cannot be implemented during emergencies. Therefore, geomorphic indices which are calibrated based on the landslide dam inventories facilitate the stability assessment of these dams.

Landslide dam inventories generally include qualitative and quantitative parameters of geographical location, landslide, dam, lake, and upstream catchment. In the current research, a comparison is made on the applicability of the existing geomorphic indices on a developed data inventory of Western Austria, Bavaria, and Northern Italy. The comparison indicates that the geometrical parameters can solely or in combination with each other stand as resisting and driving forces and that the stability assessment based on these parameters is reliable. According to the results, the volume and height of the dam are the most representative parameters of the dam's stability. However, the catchment characteristics such as area, slope, and ruggedness act as the determining destructive force. To evaluate the reliability of the methods used in the calculation or estimation of the geometric parameters, a statistical assessment is conducted based on the data from other published inventories. A wide range of variations in the mean value of the landslide and dam volume indicates the results' dependency on the study areas' geomorphological characteristics. On the other hand, the dam height of the current dataset, the datasets of Japan, New Zealand, and a worldwide database varies in only a 15 m range indicating a close estimation in different geographical regions. This emphasizes the necessity of the existence of a determining procedure for the estimation of such representative parameters in the landslide dam inventories.

How to cite: Shafieiganjeh, R., Ostermann, M., Schneider-Muntau, B., and Gems, B.: Significant parameters of a landslide dam inventory from the stability assessment aspect - data analysis based on the 'part of the Eastern Alps' data inventory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7131, https://doi.org/10.5194/egusphere-egu23-7131, 2023.

Perennial landslide dams interrupt the sediment connectivity of rivers. Although most landslide dams do not persist for more than a few days, those that do can exhibit significant sediment trapping capacity. While water can pass through or over the dam, the sediment load is trapped upstream of the dam until the dam breaks or gradually erodes, or is completely filled with deposits. The volume of sediment stored in this way can reach up to three times the volume of impounded water, as we find by back-analyzing the lake Hintersee in southeastern Germany. In this work, we reconstruct the pre-landslide topography using Petrel and then use the Gerris shallow-water flow solver with a Voellmy rheology to back-analyze this landslide-dammed lake in the Bavarian Alps. We test several landslide release scenarios and different landslide rheologies to obtain the best-fitting reconstruction of the dam topography. We then fill the landslide dam with water and sediment using simple slope algorithms and validate the results against the current topography. Finally, we compare the landslide deposit thicknesses, water depths, and trapped sediment thicknesses of our different scenarios in order to provide new insight into the damming and sediment trapping capacity of landslides.

How to cite: Argentin, A.-L., Hauthaler, T., Liebl, M., Robl, J., Hergarten, S., Prasicek, G., Salcher, B., Hölbling, D., Pfalzner-Gibbon, C., Mandl, L., Maroschek, M., Abad, L., and Dabiri, Z.: Quantification of the damming and sediment trapping capacity of landslides and their dammed lakes: the example of the Hintersee landslide dam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9848, https://doi.org/10.5194/egusphere-egu23-9848, 2023.

Large volume landslides are common features in the high-topography Andes of central Chile and Argentina (31°-35°S). Many of these landslide deposits, mostly dating from Late Pleistocene to Holocene and related to a combination of deglaciation effects, seismicity and climate pattern changes, were large enough to block the glacial valleys and form landslide dams, some of which remain holding lakes until today. In this paper, we review and investigate some conspicuous landslide dams deposits from prehistoric times in the Andes Main Range in Chile and Argentina and the Andes Frontal Range in Argentina. A bibliographic review is followed by remote sensing analysis to obtain the main morphometric parameters of the landslides and the dams, complemented with field investigations in some of them. The landslide dams related with the rock slope failures of Portillo (1.1 km³, ~13 ka), Salto del Soldado (0.2 km³, 14- 9 Ka) Mesón Alto (4.3 km³, 4.7 Ka), Cortaderas-San Nicolás (2.4 km³, Holocene) and the Pangal complex (0.3 km³ , 40-11 ka) in the Chilean Western slope and the Laguna Blanca (81 hm³, ~12 ka), Horcones (0.35 km³, ~11-8 Ka), Negro (~18 Ka), Amarillo (~8Ka), and Laguna Atuel (56 hm³,~3 Ka) landslides in the Argentinean Eastern slope are described. Eldest rock avalanches associated with a seismic triggering mechanism that generate dammed lakes were previously studied in the Central Argentinean Andes such as Tigre Dormido (1.7 km³, ~46 Ka), Placetas Amarillas (1.6 km³, ~150 ka), and Piedras Blancas (0.89 km³, ~130 Ka). In these cases, the fine lake sequences reach 30 m in thickness but no outburst terraces were identified downstream, hardly supporting their catastrophic drainage.

In both Chile and Argentina, most preserved damming collapses correspond in general to huge rock avalanches, even though some slides and debris flows also blocked narrow valleys. In general, studied ancient dams are isolated in mountain remote areas but they show evidences of catastrophic ruptures that emphases their importance in the cascade hazard scenarios. While the large majority of identified dams in the region are thousands of years old, some historic cases show that these processes still occur and pose a geological hazard. Given the large area that can be affected by outburst floods downstream the usually remote landslide sites, potentially impacting villages as well as mining, energy, and transportation infrastructure, these geohazards must be considered in risk reduction strategies in the Andean region.

How to cite: Sepulveda, S. A., Moreiras, S. M., Jeanneret, P., Correas Gonzalez, M., Bravo, K., Azanero, J., and Lara, M.: Investigation of prehistoric landslide dams in the central Andes of Chile and Argentina, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8382, https://doi.org/10.5194/egusphere-egu23-8382, 2023.

In mountainous terrains, coseismic landslide dams are catastrophic geological hazards that induce devastating and cascading effects on humanity. Identification of historical landslide dams is necessary to mitigate the long-term effects it may cause in the future. If not controlled or necessary mitigation measures are not appropriately applied, the landslide dam deposits may have longer implications in generating cascading hazards through geological time. Coseismic landslide dams in the Indian Himalayas are not explored more except for very few studies. Here, we propose a framework to examine the potential for coseismic landslide damming and analyze the possible mitigation strategies to minimize the effects. We use the framework to analyze the potential of coseismic landslide damming in Uttarakhand, India, in the western part of the Himalayas. In addition, to make a coseismic landslide dam susceptibility map, we identified around a dozen landslide dams along major river systems in Uttarakhand which were not mapped or identified earlier. We found that many landslides during the Chamoli 1999 earthquake triggered many dams. While major earthquakes after 1999 did not occur in Uttarakhand, the possibility of coseismic landslide disasters should not be overlooked, and preparedness and mitigation strategies become inevitable to avoid cascading damages by landslide damming. 

How to cite: Vashistha, A., Subramanian, S. S., and Das, J.: Co-seismic landslide damming in the Indian Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11125, https://doi.org/10.5194/egusphere-egu23-11125, 2023.