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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 m 3 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. [ABSTRACT FROM AUTHOR]

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 1m3 and bigger since 2018 and serves as automatic traffic control for an important cantonal road. In the period between January 2018 and September 2022, 6743 events were detected, which is two orders of magnitude higher activity than in stable continental cliffs. A few percent of all rockfall events reached the shadow zone, 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. [ABSTRACT FROM AUTHOR]

Six hydraulic shearing experiments have been conducted in the framework of the In-situ Stimulation and Circulation experiment within a decameter-scale crystalline rock volume at the Grimsel Test Site, Switzerland. During each experiment one out of two different shear zone types were hydraulically reactivated. An extensive monitoring system of sensors recording seismicity, pressure and strain was spatially distributed in eleven boreholes around the injection locations. As a result of the stimulation, the near-wellbore transmissivity increased up to three orders in magnitude, while jacking pressures of the stimulated structures reduced during most of the experiments. Transmissivity change, jacking pressure and seismic activity were different for the two shear zone types, suggesting that the shear zone characteristics govern the seismo-hydro-mechanical response. The elevated fracture-fluid-pressures associated with the stimulations propagated mostly along the stimulated shear zones. The absence of high-pressure signals away from the injection point for most experiments (except two out of six experiments) is interpreted as channelized flow within the shear zones. The observed deformation field within 15 m-20 m from the injection point is characterized by variable extensional and compressive strain, produced by fracture normal opening and/or slip dislocation, as well as stress redistribution related to these processes. At greater distance from the injection location, strain measurements indicate a volumetric compressive zone, in which the strain magnitude decreases with increasing distance. This compressive strain signals are interpreted as a poro-elastic far-field response to the emplacement of fluid volume around the injection interval. The exceptional hydro-mechanical data reveal that the overall stimulation effected volume is significantly larger than implied by the seismicity cloud, and can be subdivided into a primary stimulated and secondary effected zone. [ABSTRACT FROM AUTHOR]

In this contribution, we present a review of scientific research results that address seismo-hydromechanically coupled processes relevant for the development of a sustainable heat exchanger in low-permeability crystalline rock and introduce the design of the In situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to studying such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydromechanical processes that would enhance process understanding in a way that aids future stimulation design. Small-scale laboratory experiments provide fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from (1) difficulties and uncertainties in upscaling the results to the field scale and (2) relatively homogeneous material and stress conditions that lead to an oversimplistic fracture flow and/or hydraulic fracture propagation behavior that is not representative of a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales and for which access to the target rock mass with a comprehensive monitoring system is possible. The ISC experiment is designed to address open research questions in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland). Two hydraulic injection phases were executed to enhance the permeability of the rock mass. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation, and the microseismic response were monitored at a high spatial and temporal resolution. [ABSTRACT FROM AUTHOR]

In this contribution we present a review of scientific research results that address seismo-hydro-mechanical coupled processes relevant for the development of a sustainable heat exchanger in low permeability crystalline rock and introduce the design of the In-situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to study such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydro-mechanical processes that would enhance process understanding in a way that aids future stimulation design. Small scale laboratory experiments provide a fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from 1) difficulties and uncertainties in upscaling the results to the field-scale and 2) relatively homogeneous material and stress conditions that lead to an over-simplistic fracture flow and/or hydraulic fracture propagation behaviour that is not representative for a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales, and for which access to the target rock mass with a comprehensive monitoring system is possible. Only few intermediate-scale hydro-shearing and hydro-fracturing experiments have recently been performed in a densely instrumented rock mass. No such measurements have been performed on faults in crystalline basement rocks. The In-situ Stimulation and Circulation (ISC) experiment currently performed in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland) is designed to address open research questions, which could not be investigated in the required detail so far. Two hydraulic injection phases were executed to enhance the permeability of the rock mass: a hydro-shearing phase and then a hydraulic fracturing phase. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation and the micro-seismic response were monitored at a high spatial and temporal resolution. [ABSTRACT FROM AUTHOR]

Extremely-rapid, flowlike landslides can impact people and property far from their source, and predicting the initiation and runout of these events remains a challenging task. The ongoing risk analysis of the Schlucher Landslide, located near the town of Malbun, Liechtenstein, highlights the uncertainties associated with this type of analysis. This landslide, composed of clayey sand and clayey gravel, has accumulated 10s of meters of displacement in the last 3 years. Managing the risk posed by this unstable colluvial mass requires addressing the following questions: Can the Schlucher Landslide transition into an extremely-rapid flowlike landslide? If such a transition were to occur, what would be the consequence for the community located at the outflow of the Schlucher Catchment?Addressing these questions requires an understanding of potential mechanisms that can lead to catastrophic failure of the unstable mass. A number of mechanisms, including static and dynamic liquefaction, loss of true and/or apparent cohesion and shearing to residual strength have been well documented in literature, and can be identified by routine geotechnical analyses. The focus of this work is on macroscopic brittleness, a poorly understood mechanism that may have governed the failure of a number of well documented case histories that were composed of fine grained colluvium, similar to the Schlucher Landslide. Here we present detailed field observations and 3D numerical runout modelling of three extremely-rapid, flowlike landslides that occurred in fine grained colluvium: The 2014 Oso Flowslide, the 2012 Johnsons Landing Landslide and the 1973 Attachie Slide. These analyses reveal that the catastrophic runout of all three cases can be explained by the landslide debris undergoing a large, undrained strength loss. The potential for this mechanism to occur at these sites would have been difficult to identify by conventional geotechnical analyses. We then compare surface and subsurface data obtained for the Schlucher Landslide to these three cases to qualitatively assess the potential that this landslide could experience a similar undrained strength loss. The results of this work have significant implications for understanding catastrophic failure potential of fine grained colluvium, and highlight the need for further research on the mechanism of macroscopic brittleness. [ABSTRACT FROM AUTHOR]

The Moosfluh slope, located in the vicinity of the current tongue of the Great Aletsch glacier, Switzerland, hosts one of the largest active instabilities of the European Alps. Despite at this location accelerated slope displacement has been detected over the past decade, the rapid evolution observed between September and November 2016, locally reaching tens of meters, was largely unexpected. During this "crisis phase", the rock mass experienced substantial internal deformation mainly composed of toppling, formation of tensile scarps, and basal sliding. The large internal deformation caused also several local failure events in the form of single block falls and/or rock mass collapses of moderate size. Here we focus on the post-crisis, i.e. the period going between spring 2017 until today. The deformation occurring at the Moosfluh slope is still consistent and rock failure events are regularly going on, however, not in a dramatic fashion as observed in fall 2016. We show the results obtained by jointly investigating satellite, airborne, and ground based imagery, exploiting optical and radar sensors, as well as the data recorded from a local seismic network. In particular, we focus on the joint analysis of the information obtained from the optical imagery acquired with high temporal frequencies and the seismic waveforms associated to rock failure events. The combined remote sensing and geophysical dataset presented here is unique, and allows for a detailed interpretation of the rapid spatial and temporal rock mass disintegration in an alpine slope. Our results are of interest to understand mutual influences between predisposing slope instability factors (i.e., mainly due to geological, structural, and geomorphological conditions), and external driving factors (i.e., seismicity and meteo-climatic effects) on the progressive evolution of rock mass, specifically at the Moosfluh slope but also in similar case scenarios. [ABSTRACT FROM AUTHOR]

Fractured rock-masses deform in response to changes in pore pressure. In alpine catchments, groundwater flow dynamics is generally dominated by strong recharge signal from snowmelt infiltration in spring / early summer and in early winter, and punctuated by large rainstorms in snow-free periods. In crystalline rock slopes, infiltration occurs along discontinuities, such as faults and joints. Under constant normal stress joint apertures increase non-linearly during pore pressure increase, increasing the volume of saturated rock masses and leading to surface deformation. The latter can be measured with high-resolution geodetic monitoring systems and remote sensing methods such as DInSAR.In this work, we discuss temporal and spatial variations of reversible ground surface deformation measured in the Aletsch region, Switzerland. The study area is situated in the vicinity of the tongue of the Great Aletsch Glacier, central Swiss Alps, in the gneissic and granitic bedrock of the Aar massif. The valley (1550 to 2300 m.a.s.l.), is roughly oriented parallel to the main Alpine foliation (NE-SW) and to major fault zones. Total annual precipitation is less than 1 m/y, but snow depth frequently reaches 2 m during winter, with strong spatial variability. We use a network of 4 continuous Global Positioning System (cGPS) stations and 90 reflectors linked to 2 total stations (TPS), operating since 2014, to track deformation at millimetric to centimetric scale. We use weather and hydrological data from surrounding stations to estimate the timing of infiltration.At some locations in our study area we observe peak-to-peak magnitude of seasonal deformation over 2 cm, whereas other areas show no significant seasonal deformation. Measured displacement vectors are generally oriented towards the valley center in spring, when deformation rates are the highest (>0.5 mm/d). The start of the high-rate of deformation period also varies spatially. The South-facing slope starts deforming around 20 days earlier than the North-facing slope. The vertical component of motion is generally smaller than the horizontal one, and often below the noise level. Finally, we discuss possible factors (e.g. topography and slope orientation, discontinuities' orientation and density, lithology, groundwater recharge magnitudes and durations) that might influence the spatial and temporal variations of reversible deformation on the slopes adjacent to the tongue of the Great Aletsch Glacier. [ABSTRACT FROM AUTHOR]

This study is based on detailed monitoring data from a large DSGSD called Moosfluh instability, located at the current glacier tongue of the Great Aletsch Glacier (Switzerland). This about 100 Mm³ large, and up to 170 m deep toppling mode instability started to accelerate around 1990, presumably caused by increased rates of glacier ice downwasting at the landslide toe. In 2013 and 2014, when average velocities reached about 500-700 mm/a, we installed a high accuracy displacement monitoring system, composed of 2 robotized total stations measuring displacements at about 15 reflectors positioned within the active landslide, 4 GNSS stations, and 2 Time-Lapse cameras. In the fall of 2016 a dramatic increase in acceleration occurred, leading to velocities of individual landslide compartments of up to 12 m in 6 weeks. Optical imagery and digital image correlation revealed that this acceleration was caused by the rapid development of three secondary rockslide scarps, and that movement initiated at the toe of the slope and evolved upslope. To investigate the depths of movements and the subsurface kinematic mechanism in detail, we developed a new analytical model, which considers the time series of three-dimensional displacements and plunge angles of discrete points within the landslide. The application of this model leads to the conclusion that a transition from primarily toppling to sliding mode displacements occurred during fall 2016. We can trace the detailed evolution of individual compartments, showing that toppling/sliding ratios varied in both space and time. The secondary rockslides forming during this period have a depth of about 30-40 meters and volumes ranging between 1 and 5 Mm³. Planar sliding surfaces are expected to have developed at a major kink zone within the large toppling rock mass.This kinematic evolution observed at Moosfluh significantly impacts the corresponding hazard and risk assessment, as flexural toppling tends to be a self-stabilizing mechanism, whereas planar rockslides can potentially transition into catastrophic failures. The estimated potential runout length probabilities show that the main hazard would be created by the formation and subsequent breach of a rock avalanche dam in the Massa gorge below the tongue of the Great Aletsch Glacier. [ABSTRACT FROM AUTHOR]