Using satellite radar interferometry, we investigate surface deformation in the Great Aletsch Glacier region from 2015 to 2021. By applying a statistical blind source separation method on displacement timeseries, our study reveals irreversible trends near large slope instabilities, potentially indicating slope responses to the glacier’s retreat. Moreover, annual cyclic deformation indicates significant pore pressure variations in fractured bedrock slopes resulting from groundwater storage and discharge processes. These spatial variations, assessed with satellite radars, reflect changes in pore pressure and rock mass hydromechanical properties, aligning with continuous ground monitoring data. This study demonstrates the potential of using satellite interferometry to investigate slope-scale mechanical processes driven by seasonal to multiannual environmental factors in complex alpine regions. It is the first timeseries synthetic aperture radar (TS-InSAR) study in a paraglacial environment validated by spatially distributed, high-resolution ground monitoring data. Moreover, it shows the advantages of the TS-InSAR high spatial coverage and its capacity to complement ground monitoring during data interruptions at ground stations. Combining satellite data with ground-based measurements and coherent structural hypotheses opens new possibilities for studying similarly remote and less instrumented regions.

We performed an extensive analysis of C-Band SAR datasets provided by the European Space Agency (ESA) satellites ERS-1/2, Envisat ASAR, and Sentinel-1 in the period 1992-2020 aiming at reconstructing the multi-decadal spatial and temporal evolution of the surface displacements at the Brienz/Brinzauls landslide complex, located in canton Graubünden (Switzerland). To this end, we analyzed about 1’000 SAR images by applying differential interferometry (InSAR), multitemporal stacking, and Persistent Scatterer Interferometry (PSI) approaches. Moreover, we jointly considered Digital Image Correlation (DIC) on high resolution multi-temporal Digital Terrain Models (DTM) generated form airborne surveys and InSAR results to compute 3-D surface deformation fields. The extensive network of GNSS stations across the Brienz landslide complex allowed us to extensively validate the deformation results obtained in our remote sensing analyses. Here, we illustrate the limitations occurring when relying on InSAR and/or PSI measurements for the analysis and interpretation of complex landslide scenarios, especially in cases of relevant spatial and temporal heterogeneities of the deformation field. The joint use of InSAR and DIC can deliver a better picture of the evolution of the deformation field, however, not for all displacement components. Since InSAR, PSI and DIC measurements are nowadays routinely used in the framework of local investigations, as well as in regional, national and/or continental monitoring programs, our results are of major importance for users aiming at a comprehensive understanding of these datasets in landslide scenarios.

The construction/operation of ultrahigh arch dams may impose significant perturbations to surrounding mountains, resulting in landslide motions of rock slopes and endangering the safety of hydropower systems and human habitats. For example, the Laxiwa Hydropower Station in China witnessed its nearby Guobu slope displacing significantly after the reservoir impoundment and having so far displaced up to 40 m. It is of great importance to understand the mechanisms driving this large deformation. Here, we present some preliminary results from a combined remote sensing and numerical modelling investigation of this slope before, during, and after the reservoir impoundment. Analysis based on the differential interferometric synthetic aperture radar (DInSAR) data indicates that the slope had already been actively creeping at a rate of 10 cm/year (e.g. in years of 2003–2005). We develop a geological model including different rock mass compartments and various discontinuity structures as well as a realistic representation of the suspended ancient landslide. We model the coupled hydro-mechanical and creep behaviour of the slope in response to reservoir impoundment. A good agreement is reached between the simulation results and field measurements of slope displacement time series recorded at different elevations of the slope surface. Our results show that the reservoir impoundment causes notable pressure changes at the toe region of the slope, leading to strong deformations (under coupled poroelastic and primary creep effects) that propagate upslope with the ancient landslide partially reactivated. These deformations tend to decelerate significantly after the impoundment due to the transition to secondary creeps.

The stability of rock slopes along the reservoir bank is very important for achieving safe operation of a hydropower station during its impoundment period. The Guobu slope at the right bank of the Laxiwa Hydropower Station is a typical ultrahigh rock slope (700 m) and has continuously shown large deformations during and after the reservoir impoundment. In this paper, some preliminary results are presented from a combined field observation, in-situ monitoring, and experimental investigation of this slope. Based on a detailed analysis of the monitoring data of the slope and the impoundment procedure of the reservoir, it is found that the deformation of the Guobu slope shows a clear correlation with the temporal variation of the reservoir water level. According to the filed observation and inspection of the slope surface and internal deformation, the Guobu slope may be divided into three zones with their boundaries approximately defined: (i) the upper highly fractured rock mass with large deformation, (ii) the middle moderately fractured rock mass at a near-critical state, and (iii) the lower less fractured rock mass at a stable condition. Based on the observed correlation between the slope deformation and reservoir impoundment, a conceptual model interpreting the deformation mechanism of the Guobu slope is proposed. Reduction of effective stress and mechanical properties of the rock mass at the toe region of the slope, as a result of the rise of the reservoir water level, triggers the toe of the slope to deform and further induces the rock mass at the upslope region to show large deformation dominated by toppling. Furthermore, we present some experimental results to elucidate the effect of water on rock strength, which support the above conceptual model based on the mechanism of water-induced strength degradation of granitic rocks.

We present a combined experimental and numerical study of failure and damage in faulted Opalinus Clay shale around an opening at the Mont Terri Rock Laboratory, Switzerland. An experiment borehole with a diameter of 0.6 m and a length of 12.9 m intersecting a major fault zone at an acute angle of similar to 40 degrees degrees was drilled, with subsequent overbreaks closely monitored. To investigate the underlying mechanisms that lead to the observed overbreaks, we developed a 3D geomechanics model to simulate the deformation and failure behaviour of faulted Opalinus Clay shale. To represent geological structures including the major fault zone and secondary fracture sets, a site-specific fracture network was constructed. Our model captured many important geomechanical properties and responses of the faulted Opalinus Clay shale, such as anisotropy of the shale matrix, deformation of the fault zone, dislocation of secondary fractures, and growth of new cracks as well as generation of overbreaks around the opening. We compared our simulation results with in-situ experimental observation of short-term overbreak patterns along the borehole and found that the overbreak occurrence is strongly controlled by both stress conditions and geological structures. Our results indicate that the damaged zone is characterised by an inner shell and an outer shell, where the former (dominated by extensive tensile/shear cracks) has a thickness of about one quarter of the borehole diameter and the latter (dominated by sparse shear cracks) extends by half to one borehole diameter into the surrounding rock. We further elucidated the impacts of the major fault zone and secondary fracture sets as well as the borehole-fault intersection angle on the deformation, damage, and failure characteristics. The findings and insights obtained in this study have important implications for the stability evaluation of waste emplacement drifts and long-term safety assessments of nuclear waste galleries in faulted argillaceous rocks.

Prediction of rockslope dynamic evolution and catastrophic failure remains a fundamental challenge for scientists and practitioners, even though this topic has been studied for decades. Here we report about a case in the Swiss Alps, which has received worldwide attention, not only because a village was evacuated on May 12, 2023, and traffic corridors were progressively closed prior to the slope collapse, but also because this site had been studied and monitored with unprecedented detail during many years before failure. In 2023 the structural and dynamic evolution of the 2 million m3 suspended compound rockslide at Brienz/Brinzauls was closely monitored with diverse ground-based systems and continuously modeled with Voight’s creep law. Substantial deviations from this classical failure model were observed, which are in most cases not related to variations in external driving factors, but diverse internal strength degradation processes. This led to a systematic analysis of Voight’s model uncertainty and the development of an early warning system which includes supplementary early warning parameters to the classical velocity thresholds. We show how to treat the spatial and temporal variations of velocity thresholds and when they reach their applicability limit in a real-time early warning model. The unstable compartment at Brienz/Brinzauls progressively collapsed in the night of June 15, 2023, and generated a series of dry granular flows and rock mass falls, which just stopped at the Brienz settlement boundary.

Many theories about processes and conditions of rock avalanches lack field evidence, due to difficulties in monitoring such events and the rarity of accessible locations to study corresponding structures in bedrock outcrops. This study provides a detailed investigation of the basal contact zone (including the rupture/sliding surface) of the Flims rock avalanche at two sites (from the proximal and distal release area) in terms of architecture, microfabric, and formation conditions. In addition, we compare our findings with shallow seismotectonic fault zones and derive indications for processes that have occurred before, during, and after the failure of the Flims rock avalanche. Field observations document the wide natural variability of the basal contact zone architecture within the rock avalanche source area. The studied contact zone was formed at about 500 m depth as a stepped or undulating structure, few centimeters to several meters thick. It consists of chaotic breccia and locally features an up to 10 cm thick mesocataclasite, granular fault injections, and striated pavements indicating highly localized shear deformation. The pavements represent the main rupture/sliding plane of the rock avalanche and occur either as a sharp boundary to the intact bedrock or as parallel planes within mesocataclasite. In the proximal area of the source zone, a gradual increase of grain comminution towards the rock avalanche basal rupture/sliding surface suggests that most deformation and movement within the rock avalanche was concentrated in this narrow zone. In the more distal area, the deformation and movement were distributed on both the basal rupture surface and internal shear zones. Microstructural investigations of the contact zone reveal deformations older than the mesocataclasite and pavement, including mylonites and calcite veins related to the previous tectonic history, and an old healed breccia, possibly formed during pre-failure damage in this zone. The architecture of the rock adjacent to the rupture/sliding surface observed in this study shows similarities to observations from shallow seismotectonic fault zones and high-strain and high-speed shear experiments. The analogies help to understand processes that led to the formation of the rupture plane and its increased mobility: Observations of cataclasite at the basal rupture zone suggest that the movement of the rock mass first was slow (< 0.4 m/s) and crushed the rock near the basal rupture surface by constrained comminution, inducing a granular flow. An acceleration of the slip rate to over 1 m/s led to dynamic weakening and the development of a distinct rupture/sliding surface. With the formation of a thin rupture surface, several coupled processes (grain boundary sliding, frictional heating, and thermal decomposition) might have caused a further decrease of the frictional resistance on this plane, resulting in increased mobility of the rock avalanche in the source area. Evidence for these processes is given by the occurrence of rounded nano-grain structures on the pavement of the basal rupture surface, which are possible remains of thermal decarbonation. This decarbonation implies a very local temperature rise due to frictional heating (> 720 °C), less than 10 µm away from the rupture surface.

The Gotthard Base Tunnel (GBT), constructed between 2000 and 2011, is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Swiss Alps. Significant ground surface displacements reaching about 10 cm were observed during and after the tunnel construction. To gain a better understanding of the causal mechanism of such conspicuous ground deformations, we develop a three-dimensional (3D) fully-coupled hydro-mechanical model to simulate GBT-induced groundwater drainage, stress redistribution, rock mass consolidation, and fault zone deformation at the regional scale. First, we construct a geological model with topographical features, lithological units, and natural faults realistically represented. We constrain the material properties of fault zones and rock masses based on available extensive laboratory testing results and site characterisation datasets. We then simulate the tunnelling process over time, with the resulting coupled hydro-mechanical responses of faulted rock masses well captured and ground surface/subsurface displacements quantitatively analysed. The simulation results in general show a good agreement with the field monitoring data of ground surface displacement, subsurface tunnel settlement, and groundwater inflow into the tunnel. Our model indicates that ground surface displacements originate from GBT-induced water drainage and rock mass consolidation in the deep subsurface. Our results also show that the GBT construction could trigger faults to shear via drainage-induced pressure diffusion and poroelastic stressing. The research findings from our work have important implications for many groundwater drainage-related geoengineering activities such as underground excavation in alpine mountains and fluid withdrawal in subsurface reservoirs.

Catastrophic landslides characterized by runaway slope failures remain difficult to predict. Here, we develop a physics-based framework to prospectively assess slope failure potential. Our method builds upon the physics of extreme events in natural systems: the extremes so-called "dragon-kings" (e.g., slope tertiary creeps prior to failure) exhibit statistically different properties than other smaller-sized events (e.g., slope secondary creeps). We develop statistical tools to detect the emergence of dragon-kings during landslide evolution, with the secondary-to-tertiary creep transition quantitatively captured. We construct a phase diagram characterizing the detectability of dragon-kings against "black-swans" and informing on whether the slope evolves toward a catastrophic or slow landslide. We test our method on synthetic and real data sets, demonstrating how it might have been used to forecast three representative historical landslides. Our method can in principle considerably reduce the number of false alarms and identify with high confidence the presence of true hazards of catastrophic landslides.

Abstract Water infiltration into fractures is ubiquitous in crustal rocks. However, little is known about how such a progressive wetting process affects fracture stiffness and seismic wave propagation, which are highly relevant for characterizing fracture systems in situ. We study the acousto‐mechanical behavior of a free‐standing fractured granite subjected to gradual water infiltration with a downward‐moving wetting front over 12 days. We observe significant differences (i.e., by an order of magnitude) in wave amplitudes across the fractured granite compared to an intact granite, with both cases showing a strong correlation between wave amplitudes and wetting front movement. Effects of water infiltration into the fracture and surrounding matrix on seismic attenuation are captured by a numerical model with parameters constrained by experimental data. Back‐calculated fracture stiffness decreases exponentially with the wetting front migration along the fracture. We propose that moisture‐induced matrix expansion around the fracture increases asperity mismatch, leading to reduced fracture stiffness.

We present and analyze a rockfall catalog from an active landslide complex in Brienz/Brinzauls of the Swiss Alps, collected with a new Doppler radar system. This radar system provides a complete and continuous time series of rockfall events with volumes of 1 m3 and greater since 2018 and serves as automatic traffic control for an important main road. In the period between January 2018 and October 2022, 6743 events were detected, which is 2 orders of magnitude higher activity than in stable continental cliffs. A few percent of all rockfall events reached the shadow area, which hosts an important road and agricultural area. The Doppler radar data set allows us to investigate the triggering factors quantitatively. We found that the background rockfall activity is controlled by seasonal climatic triggers. In winter, more rockfalls are observed during thawing periods, whereas in summer the rockfall activity increases with hourly rainfall intensity. We also found that, due to the geological setting in an active landslide complex, increased rockfall activity occurs clustered in space and time, triggered by local displacement hotspots. Thus, monitoring spatial and temporal variations of slope displacement velocity is crucial for detailed rockfall hazard assessment in similar geological settings.

Seasonal deformation of mountain rock slopes can be driven by groundwater infiltration and depletion. Such processes could explain our field observation in the Aletsch Valley, Switzerland, where GNSS‐derived 3D annual displacement amplitudes reach 3.4 cm. However, the physical mechanisms behind such groundwater‐driven surface displacements are not well understood. Here, we develop a fully coupled hydromechanical model to simulate the relevant processes in a valley slope embedded with numerous fractures of variable sizes. The magnitude and orientation of transient annual slope surface displacement obtained from our model are in overall agreement with the field observations. The key geological factors controlling the type and magnitude of reversible mountain slope deformations are fracture network geometry, fracture aperture, and regional stress field. We show that the heterogeneity and anisotropy of bedrock hydromechanical responses, originating from depth‐dependent variations of fracture properties, play a critical role in groundwater recharge and valley slope deformation. During recharge events, pore pressure perturbations migrate downward from the groundwater table and toward the receiving stream and the deep subsurface. This process driven by pressure diffusion and poroelastic stressing develops in the subsurface with a great reach of up to a few kilometers, called critical hydromechanical response zone, and controls surface deformation patterns. During groundwater recession, this hydromechanical response zone expands downward and ground surface displacement vectors rotate upwards. Our results suggest that slope surface deformation can inform about subsurface permeability structures and pore pressure fluctuations, which have important implications for understanding groundwater flow in fractured bedrock slopes.

The water adsorption into pore spaces in brittle rocks affects wave velocity and transmitted amplitude of elastic waves. Experimental and theoretical studies have been performed to characterize moisture-induced elastodynamic variations due to macroporous effects; however, little attention has been paid to the manner in which wetting of nanopores affects elastic wave transmission. In this work, we extend our understanding of moisture-induced elastic changes in a microcracked nanopore-dominated medium where 80 % of the surface area exhibits pore diameters (also include microcrack widths) below 10 nm. We study acousto-mechanical response resulting from a gradual wetting on a free-standing intact Herrnholz granite specimen over 98 h using time-lapse ultrasonic and digital imaging techniques. Linkages between ultrasonic attributes and adsorption-induced stress/strain are established during the approach of the wetting front. We find that Gassmann theory, previously validated in channel-like nanoporous media, does not work properly in predicting the P-wave velocity increase of microcracked nanopore-dominated media at ultrasonic frequency. However, squirt flow – a theory recognized to characterize wave velocity increase and attenuation in microcracked macropore-dominated media at the pore scale – also accounts for the observed increase of P-wave velocity in microcracked nanopore-dominated media. The transmitted amplitude changes in direct P waves are explained and predicted by the elastic wave propagation within P-wave first Fresnel zone and reflection/refraction on the wetting front.

Rockfalls are distinguished from rock mass falls and rock avalanches by their physical transport mechanisms. A common term used for this differentiation is "fragmental" rockfall, where individual blocks mainly interact by impacts with the substrate along the downslope motion, which can be described by rigid body ballistics. Rockfall is very frequent in steep rock slopes, and one of the most frequent hazards to alpine traffic lines and settlements, an important process of geological mass movements along slopes, and a key mechanism for coastal cliff erosion. Most rockfall blocks or rock masses are released from steep cliffs with a high fracture density. The temporal frequency of rockfall is strongly correlated with daily rainfall magnitude, diurnal freeze-thaw cycles, the occurrence of earthquakes with magnitude greater than 4, and local rock slope stability. During a fragmental rockfall event the movement of blocks occurs in the release, transit and deposition zone. The zone boundaries are diffuse and the four types of movement – fall, bounce, roll and glide – occur everywhere. During ground impacts the blocks loose part of their translational energy and each deceleration history is unique and not comparable to the others. This energy loss depends most on the flight path, the inclination and the properties of the ground.

Die Bewegungen und die kinematische Interpretation des Rutschungskomplexes von Brienz/Brinzauls (GR) sind Gegenstand detaillierter Untersuchungen. Sie liefern Grundlagen, um die Gefährdung des Dorfes zu beurteilen und entsprechende Massnahmen zu planen. Neben den klassischen Methoden Total Station (TPS), Global Navigation Satellite Systems (GNSS) und Inklinometer kommen auch terrestrische Radarinterferometrie und digitale Bildanalyse zum Einsatz. Dieser Artikel beschreibt neue Methoden der Integration Satelliten-basierter Radar-Interferometrie (DInSAR) und der digitalen Bildkorrelationsanalyse, die ein flächendeckendes Abbild des Verschiebungsverhaltens in drei Dimensionen generieren. In der Folge beschreiben wir die Stapelung differenzieller Interferogramme von C-, L- und X-Band-Radar-Satellitendaten sowie die Integration von Ergebnissen der Interferometrie mit digitaler Korrelation von hochaufgelösten optischen und Radarbildern der Jahre 2015 bis 2020. Auf der Basis dieser Resultate werden anschliessend verschiedene Verformungskomponenten des Rutschungskomplexes ermittelt, die für die Ermittlung von Rutschungskompartimenten und ihrer Kinematik wesentlich sind. Die Ergebnisse werden mit existierenden GNSS-Messdaten validiert.

We present the results of new and repeat gallery-and borehole-scale seismic experiments carried out in two excavation damaged zones (EDZs) of 10 (gallery 08) and 20 (gallery 98) years of age at the Mont Terri Underground Rock Laboratory in St. Ursanne, Switzerland. The initial geometry and rock mass properties of the EDZs were studied during and shortly after excavation-allowing for a direct comparison of measurements collected in 2018 to those completed in the past.& nbsp;In gallery 08 parts of the EDZ remain unchanged over ten years, whilst other zones show improvement (i.e., self-sealing) or considerable degradation. In addition, velocity tomograms from 2018 measure extensive areas of p-wave velocity reduction in comparison to the surrounding rock mass at depths shallower than 3.5 m. Isolated extensile fractures are still found in boreholes up to a maximum radial extent of 4.2 m. Data from borehole interval velocity measurements and cross-hole seismic surveys from this gallery suggest the damaged zone still extends up to 1.9 m and 3.1 m radial depth.& nbsp;Refraction seismic results in gallery 98, in contrast, suggest a less pervasive, shallower (< 1.0 m) EDZ with a lower frequency of extensile fractures. The smaller circumference of this gallery can in part explain this; however, when compared to various measurements collected during and after excavation, some reduction in EDZ extent is inferable. Both borehole interval velocity measurements and seismic refraction data record p-wave velocity values higher on average than those in gallery 08 and without obvious areas of velocity reduction. Most interval velocity measurements likewise do not measure zones of decreased velocity (e.g., corresponding to rock mass damage) at this location. This suggests more self-sealing has occurred over the twenty-year post-excavation period in gallery 98 in comparison to the ten-year period in gallery 08. As repository safety depends upon the integrity of the rock mass surrounding an excavation, these results are relevant for mid-term assessments of safety (i.e., especially prior to repository closure).

Moisture variation has been noted as a driver of strains in both natural and anthropogenic bedrock environments. Similarly, increasing water content has been shown to reduce elastic stiffness in a variety of rock materials, though evidence for granites is limited. This study presents strains of an axially stressed (0.1 MPa) Herrnholz granite cylinder with ambient relative humidity alternating between 20% and 90% in a stepwise manner. At each ambient humidity level, the Young's modulus and Poisson's ratio were determined by performing a series of load and unload cycles at 1–12 hr intervals. We observed that when the ambient humidity increased from 20% to 90%, Young's modulus declined by 13% on average, and nearly returned to the initial dry value when the ambient humidity was reduced to 20%. Poisson's ratio increased by 130% in response to the same humidity change, and approximately 60% of it was reversed when dried. These changes occurred linearly with a volumetric strain of up to 8 × 10 −4 of the tested sample, equivalent to 24.5 MPa internal stress. This stress change is attributed to the generation of nanoscale adsorption stress, which includes surface adhesion pressure along pore walls and capillary pressures within characteristic pore spaces. Using a modified adsorption model, the two contributions were estimated to be 8.5 and 16 MPa, respectively. The agreement between laboratory‐derived and modeled stress change validates the proposed mechanism of adsorption‐induced strains and elastic property variations in unweathered granite.

Abstract Dry granular flows are ubiquitous, yet poorly understood mass wasting features on the Moon. Above all, their global distribution, relation to the physical environment, and drivers are poorly understood. Here, we build and deploy a convolutional neural network and map 28,101 flow features between 60°N and S by scanning through ∼150,000 Lunar Reconnaissance Orbiter images. We observe that flows are heterogeneously distributed over the Moon, where all major hotspots are located in craters and almost all hotspots are located in the nearside maria. We further observe that younger surfaces feature higher flow feature densities, while pre‐Nectarian terranes can still host flows, remaining subject to active erosion billions of years after their formation. Our observations suggest that impacts at various scales have been—and likely still are—acting as the main, global‐scale, long‐ and short‐term driver of flow occurrence, strongly influenced by the properties of the target rock material.

The old Belchen tunnel tubes in the Swiss Jura Mountains were excavated with drill-and-blast in swellable sedimentary rocks, i.e., anhydrite-rich marls (Gipskeuper) and Opalinus Clay shale (OPA). Already during construction in the 1960s both rock formations caused substantial damage to the tunnel support through high swelling pressures and heave, and in later years the tubes had to be refurbished again. Important maintenance and repair prompted the construction of a new, third Belchen tunnel tube (2016-2021) with a tunnel-boring machine (TBM). In this study we present in-situ datasets acquired to investigate the stress evolution and controlling mecha-nisms over more than four years at a monitoring section located in a strongly faulted OPA section of the new Belchen tunnel tube. The main datasets include time series of total radial pressure, radial strain, rock water content, rock and concrete temperatures, as well as details of the geological structures obtained from analyses of borehole logs and three-dimensional photogrammetric excavation face models. Finally, a series of idealised numerical simulations explore the impact of measured temperature variations on the measured total pressures, which confirm a strong temperature effect on radial pressures related to the setting of concrete and seasonal climatic variations. We find that in our monitoring section radial pressures on the tunnel support are very heterogeneous, i.e., they range between 0.5 MPa and 1.5 MPa, and still gently increasing 4 years after excavation. The measured pressures are 2-5 times greater than measured in the old Belchen tunnel tubes and similar in magnitude to swelling pressures obtained in laboratory tests. EDZ permeability measurements, water content evolution, and radial strain data from the tunnel invert suggest that swelling processes contribute to the long term radial pressure build-up. Thermo-elastic deformation and swelling might be superimposed by local reactivation of tectonic faults and gap grout cracking at crack-initiation stress levels.