The 2016 Mw 7.8 Kaikōura earthquake on New Zealand’s South Island triggered c. 30,000 landslides. Around 70% of landslides occurred in Torlesse greywacke rock mass, which is characterised by closely spaced but low-persistence joints. Most failures in this rock mass were relatively shallow rock avalanches which do not appear to follow traditional failure mechanism models. Here, we use detailed site characterisation and dynamic numerical modelling to better understand landslide hazard and risk from Torlesse greywacke slopes. Using multi-method site characterisation including 3D pixel tracking in pre- and post-earthquake aerial imagery, geomorphic mapping, rock mass characterisation, geophysical ground investigations and a geotechnical borehole, we developed engineering geological ground models for individual sites. We then used these to develop a conceptual framework of failure mechanism in Torlesse greywacke and propose a ‘joint-step-path’ failure mechanism in which rupture surface propagation occurs along pre-existing, but low-persistence joints through multiple degrees of kinematic freedom. Torlesse greywacke failures typically evolve in three main landslide failure stages – incipient, transitional and rock avalanching. Hazard can increase for the same slope when it transitions from the incipient failure stage to sliding and/or avalanching. To quantify the transition between failure stages, we analysed coseismic displacement and strain for six landslides. As many displacement based coseismic landslide susceptibility models require some threshold, above which the slope is assumed to transition into a landslide, this information could potentially serve as a useful tool. For slopes at the incipient and transitional stage, 1D maximum total strain appears to be closely correlated with source slope angle. Based on these results, we develop the ‘transitional slope strain index’ (TSSI) that combines 1D maximum total strain with source slope angle. The TSSI relates to the likelihood of a slope transitioning into a more mobile, and therefore more hazardous, rock avalanche at a given level of earthquake shaking. Dynamic numerical back-analysis of the initiation of two landslides in Torlesse greywacke supports our empirical hypotheses that landslide susceptibility in this rock mass is strongly influenced by slope angle and rock mass strength. Coseismic failure initiation is, furthermore, strongly dependent on ground motion input. The geometry of failures can be reproduced using a random Voronoi joint network and adopting residual joint strength parameters, which further lends weight to the ‘joint-step-path’ failure mechanism hypothesis.

How to cite: Singeisen, C., Massey, C., Wolter, A., Stahl, T., Bloom, C., Kellett, R., Bruce, Z., Gasston, C., Mason, D., and Jones, K.: Initiation and mechanism of rock slope failures triggered by the 2016 Mw 7.8 Kaikōura earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4552, https://doi.org/10.5194/egusphere-egu23-4552, 2023.

Rock slope instabilities cause significant risk in populated alpine areas. To anticipate the final failure, a detailed understanding of the preparatory process dynamics including all potential promoting and triggering factors is needed. While standard external and internal drivers are known, measured evidence and a quantification of their relevance at a specific site is often lacking.

Here, we present the evolution of the imminent Hochvogel summit failure (200,000–600,000 m³) over multiple decades towards the current highly sensitive system. We identified the three most relevant potential drivers at the Hochvogel instability: (i) earthquakes, (ii) seasonal and short-term meteorological effects and (iii) increasing internal stress. To quantify these, we use diverse sources of information. Earthquake catalogues and the records of the regional seismic broadband stations help to constrain known historical rock fall events at the Hochvogel. The effect of precipitation events, snowmelt and temperature is quantified by the analysis of high-resolution crack opening and rain data of the last four years. Finally, we exploit the record of our local seismic network to reveal internal rock bridge failures, rock fall activity in the flanks and the seismic stressing of the instable mass due to local earthquakes.

The current process dynamics prove a close-to-failure status of the instability. The combination of historic records and high-resolution real-time data not only makes the Hochvogel a benchmark site for alpine hazard early warning but also enables the comprehensive definition and quantification of its relevant drivers. This will improve the global understanding of rock failure dynamics and so the anticipation ability for instable rock slopes.

How to cite: Leinauer, J., Dietze, M., Knapp, S., Jokel, M., Barbosa, N., Scandroglio, R., and Krautblatter, M.: Rock slope failure evolution towards a sensitive close-to-failure system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7521, https://doi.org/10.5194/egusphere-egu23-7521, 2023.

In the coming decades with enhanced rainstorm activity, massive sediment redistribution in Alpine catchments will be a key hazard and challenge in Alpine communities. While several studies have collected data from massive rock slope failures, few studies have quantitatively assessed the cascading sediment redistribution in highly active alpine catchments. Recurrence intervals for cliffs falls are estimated at 80 years (Krautblatter et al., 2012 ), thus, observations of the subsequent sediment cascading are limited or inexistent despite their major role in landscape evolution and sediment fluxes. Digital aerial photogrammetry acquired by governmental agencies is becoming a relevant tool to better understand short landscape response to climate change. Repetitive yearly to bi-yearly orthophotos and DSM extracted from large format aerial surveys represent a valuable monitoring tool at regional scale because of their wide extent coverage (km) at a high spatial resolution (20 cm). 

This contribution reports the massive sediment redistribution that has been triggered by the multistage failure of >200.000 m³ from the Hochvogel dolomite peak during the summer of 2016. Seven true orthophotos and high-resolution aerial photogrammetric digital surface models (DSM) between 2010 and 2020 were 3D coregistered to a reference system for optimized volume calculation in steep terrain. Three consecutive differential DSMs (2010-2012, 2012-2014, 2014-2015) describe the catchment morphodynamics before the cliff fall, while, the subsequent differential DSMs (2015-2017, 2017-2018, 2018-2020) describe the morphodynamics one year, two years and four years after the cliff fall. Spectrograms from surrounding seismic stations expand the understanding of the cliff fall timing. We observe the decadal throughput of >200.000 m³ of sediment with massive sediments pulses that (i) respond with reaction times of 0-4 years and relaxation times beyond 10 years, (ii) with faster 0-2 years response times in the upper catchment (A&B) and >>2 years response times in the lower catchments, (iii) the inversion of sedimentary (>10²-10³ mm/a) to massive erosive regimes (>10² mm/a) within single years and vice versa and the (iv) dependency of redistribution to rainstorm frequency and intensities.

Krautblatter, M., Moser, M., Schrott, L., Wolf, J., Morche, D., 2012. Significance of rockfall magnitude and carbonate dissolution for rock slope erosion and geomorphic work on Alpine limestone cliffs (Reintal, German Alps). Geomorphology 167, 21–34. https://doi.org/10.1016/j.geomorph.2012.04.007

How to cite: Barbosa, N., Leinauer, J., Jubanski, J., Dietze, M., Münzer, U., Siegert, F., and Krautblatter, M.: Quantifying massive cascading sediment transport triggered by a cliff fall in a highly-active alpine basin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13129, https://doi.org/10.5194/egusphere-egu23-13129, 2023.

The investigated deep-seated rock slide is located at the valley entrance of the Münstertal in South Tyrol directing to the Swiss border. The area is attributed to the Sesvenna Crystalline of the S-charl crystalline nappe, which is mainly formed by poly-metamorphic orthogneisses with intercalations of amphibolites, phyllites, paragneisses and marbles. The rockslide extends approx. 400 m in NE-SW-direction and spans 650 m from 1450 m to the main scarp at. 2015 m a.s.l. The SE-facing slope shows a main slope inclination of approx. 35° (min. 20°, max. 80°). A total rockslide volume could be estimated at approx. 3 to 4 Million m³ by means of GIS.

The rock mass shows a flat into the slope dipping foliation (mean dip angle approx. 15°) and is highly fractured by two orthogonally orientated sets of brittle joints (set 1 and set 2). Kinematic analysis suggests direct toppling for fracture set 1 and flexural toppling for fracture set 2. Geological mapping and laboratory analysis via thin section and XRD analysis identified Muscovite-rich shearing planes and phyllonite rock types in the area of the main scarp. Weathering progresses along scarps and developed tension cracks further eroding and dissembling the rock mass.

The activation of the movement occurred in the year 2000, showing a rapid expansion since the year 2012 causing a relocation of the road underneath in 2014. Multi-temporal deformation analysis based on orthoimages, ALS and TLS were able to show high velocities of at least 9 m per month during the initial formation phase in 2014, followed by a continuous velocity reduction to mean annual values of 1 to 2.5 m per year until spring 2022. In the period spring to autumn 2022 no more movements could be detected via TLS, which raises the question of the causal reasons for the movement and the different velocities of movement. The absence of significant precipitation in spring and summer 2022 can be interpreted as a probable cause, since also previous movement velocities showed a correlation with the respective amount of precipitation.

Rock fall and rock topple events with a dimension of several thousand m³ could also be observed along outbreak recesses at the rockslide flanks, scarps and at the internal slab margins and also be detected through several TLS measurement series.

Results indicate an internal slab formation along discrete shear zones recognizable on surface as main and minor scarps. The slabs show a translational movement behaviour along a fully persistent, slightly curvilinear basal shear zone. The reason for the destabilization of the valley flank is attributed to retrogressive processes caused by long-term stress release due to topographical and hydrogeological changes by adjacent, previous rockslides situated directly below the active rockslide.

How to cite: Voit, K., Fey, C., Rechberger, C., Mair, V., and Zangerl, C.: Deformation processes and failure analysis of a deep-seated rockslide near Laatsch, South Tyrol, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2335, https://doi.org/10.5194/egusphere-egu23-2335, 2023.

Since the end of the Little Ice Age in the late 19^th century Iceland’s glaciers have experienced dramatic mass loss. Thinning outlet glaciers are exposing oversteepened rock slopes, which sometimes adjust in the form of slow slope deformations that can occasionally result in catastrophic paraglacial rock slope failures. Especially around the country’s deglaciating central volcanoes large landslides have occurred in the past decades. We describe a cluster of gravitational mass movements around the margin of the Svínafellsjökull outlet glacier in Southeast Iceland. The glacier margin is a popular tourist attraction with hundreds of visitors daily. Housing, a hotel, a gas station and the national ring-road are located within one kilometer downstream from the glacier. The largest deformation in the valley is located on the northern slope of Mt. Svínafellsfjall and is evidenced by a 2-km-long fracture system that separates an area of about 1km² and a rock volume in the range of 50-150x10⁶m³ from the mountain slope. The unstable slope is characterized by about elongated 200 sinkholes where soil cover has collapsed into underlying bedrock fractures. In several places across the slope, deep vertical bedrock fractures with no visible vertical displacement were observed. Based on morphological and structural mapping we suggest that the deformation occurs as a composite slide. Remote sensing data, eyewitnesses and field observations indicate that the onset of the deformation occurred between 2003 and 2007. This is parallel with the fastest glacier thinning rate within the 131-year record of existing data. Since 2011 the glacier surface hasn’t lowered significantly, in part due to the deposits of a large debris avalanche from 2013 on the glacial tongue which protect the glacier against ablation. The slope hasn’t shown new signs of deformation since 2018. It is however likely that the slope deformation will start again when glacier thinning continues. Even though deformation rates have been small it is crucial to continue monitoring the slope since several large rock slope failures in Iceland have shown only a short pre-failure deformation period. In a worst-case scenario a catastrophic landslide could travel across the glacier and enter two pro-glacial lakes which may lead to an outburst flood. This study shows how climate change driven glacier thinning has and likely will have further destabilizing effects on paraglacial slopes in Iceland and similar environments elsewhere.

How to cite: Ben-Yehoshua, D., Sæmundsson, Þ., Hermanns, R. L., Erlingsson, S., Helgason, J. K., Magnússon, E., and Ófeigsson, B.: The onset of a large gravitational slope deformation on Mt. Svínafellsfjall, SE Iceland., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14374, https://doi.org/10.5194/egusphere-egu23-14374, 2023.

The effect of climate-change driven increases in temperature in high mountain areas is known to enhance the rockfall risk. One of the driving mechanisms is the fracture of rock masses that previously consisted of permafrost, but that are now subject to freeze-thaw cycles. Cohesive zone models are a high-fidelity way of modelling fracture propagation, and in particular extrinsic cohesive zone models are particularly suitable to the task of modelling rock fracture behaviour, as they can capture the full range of fracturing behaviour, from quasi-static to dynamic. As cracks in the field can progress very slowly before reaching a critical point from which they accelerate rapidly, being able to model the full range of crack speeds is essential to accurately capture the physics of rockfall initiation. Here, we propose a non-smooth cohesive zone model that allows us to combine fracture mechanics with contact mechanics, meaning that it is suitable both to model the formation of cracks and the subsequent contact of surfaces as newly formed blocks fall in a unified manner. Further, writing our problem in this way allows us to include frictional behaviour within a monolithic linear complementarity problem, which enables very efficient numerical resolution. We can prove mathematically that the discrete-in-time-and-space problem is well posed for a small enough time-step, meaning that the solution is unique and will not suffer from "solution jumps" (as can happen in quasi-statics). As such, the evolution of the fracture in the rock is continuous, matching the reality, and the shape of the newly-formed rock mass can be accurately captured. Our formulation is also well-adapted for extension to fully-coupled systems that include thermal effects, so as to accurately capture freeze-thaw cycles and properly integrate permafrost behaviour, and thus have a complete model of the system under climate-change-driven loading.

How to cite: Collins-Craft, N., Bourrier, F., Gaume, J., and Acary, V.: A non-smooth cohesive zone model for rock fracture and contact, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13950, https://doi.org/10.5194/egusphere-egu23-13950, 2023.

One of the most visible consequences of climate changes in Iceland are retreating outlet glaciers and formation of proglacial lakes. It is estimated that Icelandic glaciers have lost about 16% of their mass since 1890 or over a 130-year time interval. Temperatures have been fluctuating over this period with exceptional warm period in the 1920s and 1930s followed by slightly colder interval until beginning of the 1980s. During this time outlet glacier retreated considerably but around 1970 glaciers begun to readvancing which continued until around 1995. At the end of the 20th century another turning point occurred, with higher temperatures and rapidly retreating outlet glaciers. Existing proglacial lakes expanded and many new were formed in front of the rapidly retreating ice margins. Over the last years temperature have become more stable and several outlet glaciers have been showing a readvancing phase. Glacial fluctuations have affected the stability of valley slopes above retreating outlet glaciers and their proglacial lakes. Resulting in increased frequency of mass movements and slope deformation in these high-mountain regions. In 1967 a large rockslide fell onto the Steinsholtsjökull outlet glacier and into its proglacial lake causing a GLOF.

The rockslide was approximately 20 million m³ in volume. The head scarp was around 970 m long and up to 300 m high. It fell onto the western side of the glacier and broke up its snout. Part of the rockslide material fell into a proglacial lake, in front of the ice margin, causing a large GLOF down the valley. Large amounts of sediment were transported and redistributed down-valley with the GLOF. About 20km downstream a maximum flood discharge of 2100-2700 m³/s, was estimated.

The Steinsholtsjökull 1967 GLOF, entirely overprinted the proglacial landscape in the Steinsholtsdalur valley. Similar circumstances to the valley prior to the event, now exist and are forming in glacial environments around Iceland’s present-day outlet glaciers, which highlights the urgent need to study and monitor these environments.

How to cite: Sæmundsson, Þ., Ben-Yehoshua, D., Smail, N., Hjartardóttir, Á. R., Wells, G., Belart, J. M. C., and Toschka, S.: The 1967 Steinsholtsjökull rockslide and GLOF event in light of climate change in Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14220, https://doi.org/10.5194/egusphere-egu23-14220, 2023.

In regions where rockfall in a constant occurrence, understanding rockfall evolution becomes essential. Accurate information on the quantity of rock that happens can be obtained through historical data or primary data that can be compared between the two. The Koto Panjang area is a small local mine that is quite risky because it is on the side of the main road connecting access to the two provinces. This area is geologically included in Bohorok Formation composed of gravelly mudstone deposited during the Carboniferous - Early Permian period. Three rockfalls occurred in this area in 2015, 2016 and 2016, closing access for passing vehicles. To obtain historical data comparison, 164 images of data were collected from 360 street view panoramas ranging from 2015 - 2021. The data were extracted and converted into cube images using the decompose equirectangular panorama method, and then the images were processed using Agisoft to create point clouds and compared with the latest UAV data. Based on the comparison results, it was found that significant changes of up to 4,400m3 from 2015 to 2021 occurred at several points along this area. Kinematic structure analysis from direct measurement and 3D point cloud also showed the rockfall area predominantly with direct toppling and wedge failure, which caused the previous rockfall. Therefore, this method can help reconstruct area that have experienced rockfall and provide an understanding of the retreat evolution of rockfall in the area.

How to cite: Choanji, T., Fei, L., Wolff, C., Wang, J. J., Yuskar, Y., Derron, M.-H., and Jaboyedoff, M.: Evolution of Rockfall based on SfM reconstruction of Street View and UAV data: Case study Kotopanjang, Indonesia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11649, https://doi.org/10.5194/egusphere-egu23-11649, 2023.

Yosemite National Park is a major natural asset of the USA and attracts millions of visitors each year. Its geology and geomorphology make it particularly susceptible to rockfalls, with tens of kilometers of granite cliffs up to 1000 m in height. Between 2010 and 2020, 640 rockfalls were recorded; almost half of these caused damage to the road network somewhere within the park. Approximately 300 rockfalls affected the Merced River corridor, which contains the El Portal Road, the entranceway preferred by about 30% of the visitors. In addition to causing road damage and temporary road closures, rockfalls have also caused fatalities along roadways. Because National Park policies generally preclude mitigations on natural slopes, rockfall risks along roads are mitigated through traffic management practices based on the evaluation of local hazard conditions. Due to the widespread occurrence of rockfalls and the variability of geological conditions, implementing these practices remains challenging and requires a distributed yet accurate quantitative rockfall analysis approach. We performed high-resolution 3D rockfall simulations using the Hy-Stone rockfall runout model over an area about 18 km² in size that contributes to rockfall hazards along two sections of roadway within the park, including the El Portal Road.

We set up our models using existing datasets (1m LiDAR DEM, canopy height, geological and vegetation maps), a database of Yosemite rockfall events (1857-2020), and new field surveys of infrastructure, rockfall paths and deposits, and visible damage caused by previous rockfalls. We identified rockfall sources using a morphometric approach refined by mapping rockfall evidence and additional unstable areas. Sources were classified into “cliff” and “roadcut” (engineered) categories. We mapped Quaternary deposits at the scale of consideration, reclassified vegetation types in categories relevant to rockfall interactions, and produced a unique condition map for model parametrization.

We calibrated Hy-Stone parameters (initial velocity, impact restitution, and rolling friction coefficients) by the back analysis of occurred rockfalls, for which field-based evidence was collected by NPS and USGS. We used post-event aerial pictures of the 2017 Parkline rockfall to map the location and size of 4700 blocks, producing a reference block size distribution for the simulations. Model parameters were calibrated by optimizing the fit between simulated and observed arrest locations and volumes.

We performed forward simulations over the study area considering “cliff” rockfall sources and two different block volume scenarios: a) realistic, stochastically variable volumes; b) worst-case, constant volume (100 m³). An additional simulation considered roadcut sources with variable block volumes. Results were extracted as raster maps of block frequency, velocity, energy, and height and validated against the historical and field databases, making it possible to perform a quantitative evaluation of rockfall susceptibility using the Rockfall Hazard Vector (RHV) method.

Our models combine robust 3D simulations with detailed field data, allowing the characterization of rockfall susceptibility over a large area with the spatial accuracy typical of site-specific studies. This provides robust inputs to quantitative risk analysis that will allow optimizing risk management and granting safer access to the park.

How to cite: Agliardi, F., Frattini, P., Stock, G. M., Demonti, S., Franzosi, F., Lanfranconi, C., and Collins, B. D.: Supporting rockfall risk management along roadways in Yosemite National Park, California (USA) by field-constrained high-resolution 3D modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11263, https://doi.org/10.5194/egusphere-egu23-11263, 2023.

Wooden rockfall barriers offer a sustainable solution to rockfall problems, while the full potential of wood remains untapped with increasing demands for natural hazards management in a changing climate. In Switzerland some of the first rockfall protection barriers were made from recycled wooden railway sleepers. Others sourced round wood beam elements from local mountain forests providing protection from natural hazards. However, advances in steel-wire net rockfall protection solutions have superseded wooden alternatives and this sustainable solution is being neglected.

With the aim of documenting existing wooden rockfall barriers and their protective capacity. Field investigations of existing wooden rockfall barriers, their construction design, remaining wood quality and moisture content, along with environmental conditions and evidence of rockfall impact events were conducted. This contribution focuses on a rockfall event that impacted one of the documented wooden barriers, causing damages to the beams and system structure. Rockfall impact scars were traced from its release source to the impact with the wooden barrier and are used to apply classical methods in rockfall trajectory analysis. Damages to the wooden barrier system are used to back calculate the rockfall impact energies and compared to the trajectory analysis of the event. Through this study an initial foundation in defining the protective capacity of wooden rockfall barriers has been established. Initial results indicate a higher energy dissipation capacity of wooden rockfall protection barriers than previously assumed and warrants further investigation of this sustainable rockfall protection solution.

How to cite: Glover, J. and Fröhlich, A.: Wooden rockfall barrier assessment and impact analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16570, https://doi.org/10.5194/egusphere-egu23-16570, 2023.

Rockfalls could be catastrophic for their inherent characteristics such as limited precursor deformation, unforeseeable movement, and extreme velocity. Potential damages in a rockfall event are mostly associated with blocks reaching vulnerable elements during their descent down the slope. The block volumes involved in a rockfall as well as detachment locations, trajectories and velocity along a slope are the parameters that directly determine the intensity of a rockfall hazard. Therefore, there is a dire need to develop effective evaluation strategies for rockfall phenomena through efficient monitoring and analysis techniques. Recent years have witnessed significant developments in the monitoring, analytical and physical methods for the study of rockfall phenomena. Improvements in the use of laser scanning, and drone photogrammetry have allowed to exploit high-resolution virtual outcrop models (VOMs) and derive accurate information about slope evolution. Rock falls are strictly related to fracture patterns pervading the rock mass. Hence, kinematic analyses can quantify the susceptibility to failure of a rock block. Moreover, discontinuity extraction represents the key data to investigate the spatial distribution of fractures and consequently to determine the potential rock block volumes. The trajectories of the rock fragments depend on the slope geometry and the characteristics of the propagation zone, local asperities, and the mechanical attributes of the exposed bedrock and soil cover.

The present study concerns the evaluation of rockfall activity, susceptibility, and hazard modelling of the Poggio Baldi landslide (Central Italy). The Poggio Baldi landslide is affected by frequent rockfalls, and it is being monitored for several years with multiple remote sensing instruments. It is home to a permanent natural monitoring laboratory managed by the Department of Earth Sciences of the Sapienza University of Rome and NHAZCA SRL. Over the years, many surveys and investigations have been carried out using modern remote sensing techniques to capture active gravitational processes.

Here, we introduce a new approach combining 3D and 2D VOM to assess rockfall activity and the associated hazard. Most active rockfall source sectors were found using 3D change detection on multitemporal VOMs, thus suggesting the state of activity of the rock scarp. In these sectors, we thoroughly surveyed the discontinuity sets and their patterns, such as spacing and persistence by integrating data from UAV-based photogrammetric point clouds and orthoimages. These data were then used to calculate the volume of the typical rock blocks characterizing each area. Moreover, we implemented a GIS-based modified kinematic method to assess the failure susceptibility of the rock scarp using slope morphometry and discontinuity orientations. Finally, to simulate the potential runout of falling blocks from the most active and susceptible areas of the slope, rockfall trajectory simulations were performed on a physical characteristics-based GIS model. The results of kinematic susceptibility and rockfall runout were then statistically assessed by comparing them with real depletion and accumulation areas derived by the multitemporal VOMs with a time span of 3 years. Through this approach, it was possible to perform detailed rockfall hazard simulations for each source area using specific structural/geomechanical data.

How to cite: Mastrantoni, G., Kundu, J., Santicchia, G., Cosentino, A., Robiati, C., and Mazzanti, P.: Rockfall hazard assessment of the Poggio Baldi landslide by combining 3D and 2D multitemporal remote sensing data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16048, https://doi.org/10.5194/egusphere-egu23-16048, 2023.

The coast of Ibiza is characterized by a large number of small coves and pocket beaches, impended by cliffs carved in relatively weak rocks such as calcarenites and marls. Due to its structural, geomorphological and lithological characteristics these cliffs are subjected by the widespread occurrence of rockfalls. Despite their moderate magnitude, these represent a major threat to the safety of tourists during the long touristic season of the island. This threat has increased in the last decades, as the island of Ibiza has become one of the major tourist destination in Europe. The management of rockfall risk is particularly complex, since risk varies locally according to both the hazard at the sites and the number of tourist attending the different beaches.

In this perspective, we performed an island-wide high-resolution 3D rockfall simulations, exploiting the capabilities of the Hy-Stone rockfall runout model along 210 km of the Ibiza coastline, in order to characterise rockfall risk at regional scale. Rockfall source areas have been identified using a morphometric approach with a slope threshold value of 50° obtained by a 2x2 m Lidar, further refined by mapping rockfall evidence and additional unstable spots. In order to characterize the slope surface and its interaction to rockfalls, as a basis for model parametrization, we combined lithology and land use. The first was classified with a geotechnical approach based on the average value of resistance to simple uniaxial compression into thrre classes: “weak rocks”, “moderately – hard rocks” and “hard rocks”, along with the Quaternary deposits. The land use has been classified into 8 classes, including forested, non-forested, and urban areas. The calibration of the restitution and friction surface parameters was obtained by back analysis of the 2017 rockfall in Es Cubells, for which field-based evidence was collected. The results of the rockfall simulations have been used within a multicriteria risk assessment by adopting the AHP weighting methodology. In addition to the results of the models, the multicriteria analysis includes indicators related to number of tourist and the presence of buildings, both obtained by a dataset provided by the Emergencies General Management and Interior of the Government of the Balearic Islands. The multicriteria analysis made it possible to rank the different beaches according to their rockfall risk, thus contributing to the risk management and mitigation plan strategies of the sites.

Two of the most at risk sites, Es Cubells and Cala d’Hort, were further simulated at the local scale, based on high-resolution data collected thought UAV survey and field activity.

In conclusion, this research combined robust 3D simulations and detailed field data to characterize rockfall hazard both at regional and local scale for the Ibiza coastal cliffs. Moreover, through the multicriteria analysis it provides a qualitative risk estimation that allows the optimization of the risk management and planning for the beaches of the island.

How to cite: Frattini, P., Bertolo, C., Agliardi, F., Sarro, R., and María Mateos, R.: Rockfall hazard and risk along the coast of Ibiza (Balearic Islands, Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16182, https://doi.org/10.5194/egusphere-egu23-16182, 2023.

Manikaran town of Kullu district, Himachal Pradesh, NW Himalaya, India is a famous hotspot for hot springs, ancient Ram Mandir, and Gurudwara Sahib, which makes it a major tourist attraction. Over the past years, the number of tourists visiting Manikaran to explore the hot springs and ancient temples has increased exponentially. One major rockfall event occurred in Manikaran town in August 2015, destroying the four-story Gurudwara building, killing nearly 10 people, and injuring 15 people sleeping in the Gurudwara’s Sarai. Manikaran and surrounding areas witness rockfall activity every monsoon. These past events and the attraction of tourists to this place make it a very risky zone that needs to be studied closely. In this study, a holistic approach comprising geological field investigation, geomorphic mapping, field-based rockfall dataset (rock shape and volume), generation of high-resolution digital elevation model (DEM) using RTK-DGPS, and numerical modelling using open-source software SICONOS was conducted. During field investigations, it was found that the August 2015 rockfall event was not only a result of a single rock block affecting the Gurudwara. Instead, the main rockfall source block triggered the chain of rockfall events by remobilizing the static blocks present on the surface of the runout path of the moving block. A novel rockfall propagation model was developed by incorporating the rock-rock interaction using the rigid body approach in SICONOS software to complement the real August 2015 rockfall event in Manikaran. A comparative rockfall hazard assessment was conducted by comparing the rockfall trajectory simulation with and without static blocks present on the slope. Consequently, two different scenarios of rockfall simulations were generated for Manikaran such that realistic rockfall events can be captured for predicting future rockfall hazards in Manikaran. This study considers for the first time the role of static blocks present on the surface in rockfall propagation models and has potential applications across a wide range of rockfall-prone areas, especially those where large static rock blocks are found in the run-out path of moving rock blocks during rockfalls.

How to cite: Dhiman, R. K., Bourrier, F., and Thakur, M.: The study of remobilization of static blocks present on the terrain due to rockfall impact: a comparative assessment of rockfall hazard in Manikaran, NW Himalaya, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1947, https://doi.org/10.5194/egusphere-egu23-1947, 2023.

Half tunnels occurring as ‘overhangs’ within steep slopes of massive and hard rock mass have advantages over full tunnels or open excavations as they are economical and take short time in construction. Because of their sporadic occurrence along NH-05 the stability analysis of half tunnels in these areas is undone and some are still unexplored. These half tunnels are excavated through a highly jointed/fractured rock slopes which may be the threat to people’s lives and can disrupt the transportation in any time if any reinforcement is not given. The detached rock blocks from these half tunnels and surrounding rocky slopes took many local peoples and tourists lives in the past. These half tunnels in the Himalayan regions have existed since many years despite any reinforcement given to them. The stability analysis of these fractured and jointed rock mass associated with half tunnels are needs to be carried out and requires proper remedial measures and reinforcements to avoid any mishap in future. Therefore, in this regard, the present study endeavors the slope stability assessment of one such half tunnel, a stretch of ca.1km located near Thopan on NH- 05 in Kinnaur district, Himachal Pradesh, India. Basic Rock Mass Rating (RMR basic) has been used to classify and evaluate rock mass exposed in this half tunnel. Total six slopes have been chosen for stability assessment. Rock mass classification done by Basic Rock Mass Rating (RMR_basic) categorizes all six rock slopes into class II (good rock).  Continuous Slope Mass Rating (CSMR) was used to evaluate the stability of these six slopes in which 5 slopes fall into the Class V category and one slope fall into Class III category. The kinematic analysis demonstrates that wedge failure is the most common and likely failure type amongst the three failures (wedge, planar, and toppling) in the jointed rock slopes of half tunnel. The Factor of Safety (FoS) was also calculated for all the six slopes having the lowest CSMR values in the wedge failure case. All these 6 slopes are unstable showing FoS values less than one.

 Keywords: Slope Stability, NW Himalaya, Half Tunnels, Rock slopes, RMR, CSMR, Kinematic Analysis, FoS, Swedge model.

How to cite: Parkash, J., Thakur, M., Singh, J., and Negi, V. S.:  Slope Stability Assessment of Half Tunnel near Thopan area on National Highway-05 in Kinnaur District, NW Himalaya, India using Empirical, Kinematic and Limit Equilibrium methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4347, https://doi.org/10.5194/egusphere-egu23-4347, 2023.

The Himalayan geology is complex and fragile in nature. Many landslides are witnessed every year in the region and the occurrence of landslides drastically increases during monsoon. An alarming increase in landslide occurrences has been noticed, which sometimes are attributed to anthropogenic activities. In the present article, stability assessment of a road-cut rock slope site has been discussed. The most recent landslide at the slope site occurred on July 9^th, 2022. The rock slope site is situated on Dehradun – Mussoorie highway, and is 29 km away from Mussoorie and 22 km from Dehradun in Uttarakhand state of India. The location is strategically important and poses risk of landslide hazards that can cause loss of human lives and resources. After the landslide occurred, the scarp of the rock slide was of the height of nearly 80 m above road level (1370 m above MSL) with slope height more than 150 m. The entrainment of the slided debris mass was of the extent of 70 m below road level. The preliminary data after the rock-slide at the slope site were recorded and collected such as slope images, slope attributes, joint attributes, joint roughness, and rock chunks. Google earth imageries of past years were observed for the slope site and 1^st instance of instability was recorded in 2017, followed by another slide in 2019. Lastly, a major slide occurred in 2022. Point-load strength index (PLSI) tests on irregular rock chunks were performed as per IS – 8764 (1998) and UCS of the intact rock was derived using empirical correlation. Normal distribution was applied on the PLSI results to better assess the UCS of the intact rock. The probabilistic mean of the UCS was 24.21 MPa. Rock mass at the slope site was classified using Rock Mass Rating (RMR) and Q-slope classification system. Evaluated RMR and Q values were 37 and 0.073 respectively. A general impression from the derived values was that the rock mass was of poor quality with calculated safe cut slope angle of 42.3°. In the present case, the slope inclination lies between 60° - 70° on an average and can be termed under the category of unstable slopes. Further, Slope Mass Rating (SMR) was implemented on the slope site. The site was categorized in class IV and termed as unstable with probability of failure of 0.6 and type of failure as planar or big wedges. To be more certain and specific about the type of failure, kinematic analysis was performed in DIPS. It was determined that the rock slope has the probability of direct toppling by 0.33 and wedge sliding by 0.33. Hence, proper mitigation and stabilisation measures should be adopted to avoid any potential hazard.

How to cite: Chandel, A., Gupta, N., and Singh, M.: Stability assessment of a recurring rockslide on Dehradun – Mussoorie highway in the Uttarakhand state of India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11153, https://doi.org/10.5194/egusphere-egu23-11153, 2023.