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Understanding the dynamics of slope instabilities is critical to mitigate the associated hazards, but their direct observation is often difficult due to their remote locations and their spontaneous nature. Seismology allows us to get unique information on these events, including on their dynamics. However, the link between the properties of these events (mass and kinematics) and the seismic signals generated is still poorly understood. We conducted a controlled rockfall experiment in the Riou Bourdoux torrent (southern French Alps) to try to better decipher those links. We deployed a dense seismic network and inferred the dynamics of the block from the reconstruction of the 3D trajectory from terrestrial and airborne high-resolution stereophotogrammetry. We propose a new approach based on machine learning to predict the mass and the velocity of each block. Our results show that we can predict those quantities with average errors of approximately 10 % for the velocity and 25 % for the mass. These accuracies are as good as or better than those obtained by other approaches, but our approach has the advantage in that it does not require the source to be localised, nor does it require a high-resolution velocity model or a strong assumption on the seismic wave attenuation model. Finally, the machine learning approach allows us to explore more widely the correlations between the features of the seismic signal generated by the rockfalls and their physical properties, and it might eventually lead to better constraints on the physical models in the future. [ABSTRACT FROM AUTHOR]

Synthetic Aperture Radar (SAR) acquisition can be performed from satellites or from the ground by means of a so- called GB-InSAR (Ground-Based Interferometry SAR), but the signal emission and the output image geometry slightly differ between the two acquisition modes. Those differences are rarely mentioned in the literature. This paper proposes to compare satellite and GB-InSAR in terms of (1) acquisition characteristics and parameters to consider; (2) SAR image resolution; (3) geometric distortions that are foreshortening, layover and shadowing. If in the case of satellites SAR, the range and azimuth resolutions are known and constant along the orbit path, in the case of GB-InSAR their values are terrain-dependent. It is worth estimating the results of a GB-InSAR acquisition one can expect in terms of range and azimuth resolution, Line of Sight (LoS) distance and geometric distortions to select the best installation location when several are possible. We developed a tool which estimates those parameters from a Digital Elevation Model (DEM), knowing the GB-InSAR and the Slope of Interest (Sol) coordinates. This tool, written in MATLAB, was tested on a simple synthetic point cloud representing a cliff with a progressive slope angle to highlight the influence of the Sol geometry on the acquisition characteristics and on two real cases; cliffs located in Switzerland, one in the Ticino canton and on in the Vaud canton. [ABSTRACT FROM AUTHOR]

Many examples of rockfall simulation software provide great flexibility to the user at the expense of a hardly achievable parameter unification. With sensitive site-dependent parameters that are hardly generalizable from the literature and case studies, the user must properly calibrate simulations for the desired site by performing back-calculation analyses. Thus, rockfall trajectory reconstruction methods are needed. For that purpose, a computer-assisted videogrammetric 3D trajectory reconstruction method (CAVR) built on earlier approaches is proposed. Rockfall impacts are visually identified and timed from video footage and are manually transposed on detailed high-resolution 3D terrain models that act as the spatial reference. This shift in reference removes the dependency on steady and precisely positioned cameras, ensuring that the CAVR method can be used for reconstructing trajectories from witnessed previous records with nonoptimal video footage. For validation, the method is applied to reconstruct some trajectories from a rockfall experiment performed by the WSL Institute for Snow and Avalanche Research SLF. The results are compared to previous ones from the SLF and share many similarities. Indeed, the translational energies, bounce heights, rotational energies, and impact positions against a flexible barrier compare well with those from the SLF. The comparison shows that the presented cost-effective and flexible CAVR method can reproduce proper 3D rockfall trajectories from experiments or real rockfall events. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of slope instabilities is critical to mitigate the associated hazards but their direct observation is often difficult due to their remote locations and their spontaneous nature. Seismology allows to get unique information on these events, including on their dynamics. However, the link between the properties of these events (mass and kinematics) and the seismic signals generated are still poorly understood. we conducted a controlled rockfall experiment in the Riou-Bourdoux torrent (South French Alps) to try to better decipher those links. We deployed a dense seismic network and inferred the dynamics of the block from the reconstruction of the 3D trajectory from terrestrial and airborne high-resolution stereo-photogrammetry. We propose a new approach based on machine learning to predict the mass and the velocity of each block. Our results show that we can predict those quantities with average errors of approximately 10 % for the velocity and 25 % for the mass. These accuracies are as good as or better than those obtained by other approaches, but our approach has the advantage of not requiring to localize the source and an a priori knowledge of the environment, nor of making a strong assumption on the seismic wave attenuation model. Finally, the machine learning approach allows us to explore more widely the correlations between the features of the seismic signal generated by the rockfalls and their physical properties, and might eventually lead to better constrain the physical models in the future. [ABSTRACT FROM AUTHOR]

We propose an explicit GPU-based solver within the material point method (MPM) framework using graphics processing units (GPUs) to resolve elastoplastic problems under two- and three-dimensional configurations (i.e. granular collapses and slumping mechanics). Modern GPU architectures, including Ampere, Turing and Volta, provide a computational framework that is well suited to the locality of the material point method in view of high-performance computing. For intense and non-local computational aspects (i.e. the back-and-forth mapping between the nodes of the background mesh and the material points), we use straightforward atomic operations (the scattering paradigm). We select the generalized interpolation material point method (GIMPM) to resolve the cell-crossing error, which typically arises in the original MPM, because of the C0 continuity of the linear basis function. We validate our GPU-based in-house solver by comparing numerical results for granular collapses with the available experimental data sets. Good agreement is found between the numerical results and experimental results for the free surface and failure surface. We further evaluate the performance of our GPU-based implementation for the three-dimensional elastoplastic slumping mechanics problem. We report (i) a maximum 200-fold performance gain between a CPU- and a single-GPU-based implementation, provided that (ii) the hardware limit (i.e. the peak memory bandwidth) of the device is reached. Furthermore, our multi-GPU implementation can resolve models with nearly a billion material points. We finally showcase an application to slumping mechanics and demonstrate the importance of a three-dimensional configuration coupled with heterogeneous properties to resolve complex material behaviour. [ABSTRACT FROM AUTHOR]

The generation of a tsunami by a landslide is a complex phenomenon that involves landslide dynamics, wave dynamics and their interaction. Numerous lives and infrastructures around the world are threatened by this phenomenon. Predictive numerical models are a suitable tool to assess this natural hazard. However, the complexity of this phenomenon causes such models to be either computationally inefficient or unable to handle the overall process. Our model, which is based on shallow-water equations, has been developed to address these two problems. In our model, the two materials are treated as two different layers, and their interaction is resolved by momentum transfer inspired by elastic collision principles. The goal of this study is to demonstrate the validity of our model through benchmark tests based on physical experiments performed by Miller et al. (2017). A dry case is reproduced to validate the behaviour of the landslide propagation model using different rheological laws and to determine which law performs best. In addition, a wet case is reproduced to investigate the influence of different still-water levels on both the landslide deposit and the generated waves. The numerical results are in good agreement with the physical experiments, thereby confirming the validity of our model, particularly concerning the novel momentum transfer approach. [ABSTRACT FROM AUTHOR]

We present an efficient MATLAB-based implementation of the material point method (MPM) and its most recent variants. MPM has gained popularity over the last decade, especially for problems in solid mechanics in which large deformations are involved, such as cantilever beam problems, granular collapses and even large-scale snow avalanches. Although its numerical accuracy is lower than that of the widely accepted finite element method (FEM), MPM has proven useful for overcoming some of the limitations of FEM, such as excessive mesh distortions. We demonstrate that MATLAB is an efficient high-level language for MPM implementations that solve elasto-dynamic and elasto-plastic problems. We accelerate the MATLAB-based implementation of the MPM method by using the numerical techniques recently developed for FEM optimization in MATLAB. These techniques include vectorization, the use of native MATLAB functions and the maintenance of optimal RAM-to-cache communication, among others. We validate our in-house code with classical MPM benchmarks including (i) the elastic collapse of a column under its own weight; (ii) the elastic cantilever beam problem; and (iii) existing experimental and numerical results, i.e. granular collapses and slumping mechanics respectively. We report an improvement in performance by a factor of 28 for a vectorized code compared with a classical iterative version. The computational performance of the solver is at least 2.8 times greater than those of previously reported MPM implementations in Julia under a similar computational architecture. [ABSTRACT FROM AUTHOR]

In this contribution, we present an efficient MATLAB-based implementation of the material point method (MPM) and its most recent variants. MPM has gained popularity over the last decade, especially for problems in solid mechanics in which large deformations are involved, i.e., cantilever beam problems, granular collapses and even large-scale snow avalanches. Although its numerical accuracy is lower than that of the widely accepted finite element method (FEM), MPM has been proven useful in overcoming some of the limitations of FEM, such as excessive mesh distortions. We demonstrate that MATLAB is an efficient high-level language for MPM implementations that solve elasto-dynamic and elasto-plastic problems, such as the cantilever beam and granular collapses, respectively. We report a computational efficiency factor of 20 for a vectorized code compared to a classical iterative version. In addition, the numerical efficiency of the solver surpassed those of previously reported MPM implementations in Julia, ad minima 2.5 times faster under a similar computational architecture. [ABSTRACT FROM AUTHOR]

In the morning of 23 August 2017, around 3 ×106 m 3 of granitoid rock broke off from the eastern face of Piz Cengalo, southeastern Switzerland. The initial rockslide–rockfall entrained 6 ×105 m 3 of a glacier and continued as a rock (or rock–ice) avalanche before evolving into a channelized debris flow that reached the village of Bondo at a distance of 6.5 km after a couple of minutes. Subsequent debris flow surges followed in the next hours and days. The event resulted in eight fatalities along its path and severely damaged Bondo. The most likely candidates for the water causing the transformation of the rock avalanche into a long-runout debris flow are the entrained glacier ice and water originating from the debris beneath the rock avalanche. In the present work we try to reconstruct conceptually and numerically the cascade from the initial rockslide–rockfall to the first debris flow surge and thereby consider two scenarios in terms of qualitative conceptual process models: (i) entrainment of most of the glacier ice by the frontal part of the initial rockslide–rockfall and/or injection of water from the basal sediments due to sudden rise in pore pressure, leading to a frontal debris flow, with the rear part largely remaining dry and depositing mid-valley, and (ii) most of the entrained glacier ice remaining beneath or behind the frontal rock avalanche and developing into an avalanching flow of ice and water, part of which overtops and partially entrains the rock avalanche deposit, resulting in a debris flow. Both scenarios can – with some limitations – be numerically reproduced with an enhanced version of the two-phase mass flow model (Pudasaini, 2012) implemented with the simulation software r.avaflow, based on plausible assumptions of the model parameters. However, these simulation results do not allow us to conclude on which of the two scenarios is the more likely one. Future work will be directed towards the application of a three-phase flow model (rock, ice, and fluid) including phase transitions in order to better represent the melting of glacier ice and a more appropriate consideration of deposition of debris flow material along the channel. [ABSTRACT FROM AUTHOR]

A landslide-generated tsunami is a complex phenomenon that involves landslide dynamics, wave dynamics and their interaction. Numerous lives and infrastructures around the world are threatened by these events. Predictive numerical models are a suitable tool to assess this natural hazard. However, the complexity of this phenomenon causes such models to be either computationally inefficient or unable to handle the overall process. Our model, which is based on shallow water equations, is developed to address these two problems. In our model, the two materials are treated as two different layers, and their interaction is resolved by momentum transfer inspired by elastic collision principles. The goal of this study is to demonstrate the validity of our model through benchmark tests based on physical experiments performed by Miller et al. (2017). A dry case is reproduced to validate the behaviour of the landslide propagation model using different rheological laws and to determine which law performs the best. In addition, a wet case is reproduced to investigate the influence of different still water levels on both the landslide deposit and the generated waves. The numerical results are in good agreement with the physical experiments, thereby confirming the validity of our model, particularly concerning the novel momentum transfer approach. [ABSTRACT FROM AUTHOR]

In the morning of 23 August 2017, around 3 million m³ of granitoid rock broke off from the east face of Piz Cengalo, SE Switzerland. The initial rock slide-rock fall entrained 0.6 million m³ of a glacier and continued as a rock(-ice) avalanche, before evolving into a channelized debris flow that reached the village of Bondo at a distance of 6.5 km after a couple of minutes. Subsequent debris flow surges followed in the next hours and days. The event resulted in eight fatalities along its path and severely damaged Bondo. The most likely candidates for the water causing the transformation of the rock avalanche into a long-runout debris flow are the entrained glacier ice and water originating from the debris beneath the rock avalanche. In the present work we try to reconstruct conceptually and numerically the cascade from the initial rock slide-rock fall to the first debris flow surge and thereby consider two scenarios in terms of qualitative conceptual process models: (i) entrainment of most of the glacier ice by the frontal part of the initial rock slide-rock fall and/or injection of water from the basal sediments due to sudden rise in pore pressure, leading to a frontal debris flow, with the rear part largely remaining dry and depositing mid-valley; and (ii) most of the entrained glacier ice remaining beneath/behind the frontal rock avalanche, and developing into an avalanching flow of ice and water, part of which overtops and partially entrains the rock avalanche deposit, resulting in a debris flow. Both scenarios can be numerically reproduced with the two-phase mass flow model implemented with the simulation software r.avaflow, based on plausible assumptions of the model parameters. However, these simulation results do not allow to conclude on which of the two scenarios is the more likely one. Future work will be directed towards the application of a three-phase flow model (rock, ice, fluid) including phase transitions, in order to better represent the melting of glacier ice, and a more appropriate consideration of deposition of debris flow material along the channel. [ABSTRACT FROM AUTHOR]

Reconstructions of failure surfaces (prior to potential landslides or after their release), landslide deposits, or other palaeotopographic features are important for hazard and erosion assessment. The volumes involved in landslide and failure surfaces constrain the propagation of a landslide, and knowledge of the past topography helps us to understand these hazards. Some methods exist to characterise landslide geometry, but these methods usually require monitoring information. This study tries to assess the validity of the sloping local base level (SLBL) method for this purpose. Two sets of airborne lidar digital elevation models (DEMs) of the Kii Peninsula (Japan) are used: the first one was acquired before Typhoon Talas, and the second one was acquired after. A total of 70 deep-seated landslides occurred during this event between 2 and 5 September 2011. This study shows that the SLBL method is efficient using either the slope deformations identifiable on the DEM before the release of the landslide or a reliable 2.5-D failure surface created by using both DEMs (the 2.5-D corresponds to a surface which has only one z value for each x – y coordinate; in other words, no true vertical topography or overhang can be represented perfectly). In addition, this method allows for the reconstruction of eroded deposits and buried valleys. Most of the volumes estimated are within ±35 % of the estimation made by Chigira et al. (2013), and the coefficients of expansion range from 10 % to 25 %. These results show considerable sensitivity to the parameters used for the reconstruction of the landslide volume estimations and demonstrate the need for an efficient and fast tool to reconstruct potential landslide geometries or histories. [ABSTRACT FROM AUTHOR]

Switzerland is threatened by many natural hazards. Many events occur in built-up environments, affecting infrastructure, buildings, and transportation networks, occasionally producing expensive damages. This expense is why large landslides are generally well studied and monitored in Switzerland to reduce the financial and human risks. However, there is a lack of data on small events, which have recently affected roads and railways. Therefore, in this study, all of the reported natural hazard events that have affected Swiss transportation networks since 2012 were collected in a database. More than 800 events affecting roads and railways were recorded within in a 5-year period from 2012 to 2016. These events are classified into six classes: earth flow, debris flow, rockfall, flood, snow avalanche, and others. Data from Swiss online press articles were sorted by Google Alerts. The search was based on more than 30 keywords in three languages (Italian, French, and German). After verification that the article was related to an actual event that affected a road or a railway track, it was studied in detail. We collected information on more than 170 attributes of events, such as the event date, event type, event localization, meteorological conditions, impacts and damages on the track, and human damages. From this database, a variety of trends over the 5-year period can be observed in the event attributes, particularly the spatial and temporal distributions of the events, and their consequences on traffic (closure duration, deviation, costs of direct damage). The database is imperfect due to the short period of data collection, but it highlights the non-negligible impact of small natural hazard events on roads and railways in Switzerland at a national level. This database contributes to understanding and quantification of these types of events and better integration in risk assessment. [ABSTRACT FROM AUTHOR]

We discuss here different challenges and limitations of surveying rock slope failures using 3-D reconstruction from image sets acquired from street view imagery (SVI). We show how rock slope surveying can be performed using two or more image sets using online imagery with photographs from the same site but acquired at different instances. Three sites in the French alps were selected as pilot study areas: (1) a cliff beside a road where a protective wall collapsed, consisting of two image sets (60 and 50 images in each set) captured within a 6-year time frame; (2) a large-scale active landslide located on a slope at 250m from the road, using seven image sets (50 to 80 images per set) from five different time periods with three image sets for one period; (3) a cliff over a tunnel which has collapsed, using two image sets captured in a 4-year time frame. The analysis include the use of different structure from motion (SfM) programs and a comparison between the extracted photogrammetric point clouds and a lidar-derived mesh that was used as a ground truth. Results show that both landslide deformation and estimation of fallen volumes were clearly identified in the different point clouds. Results are site- and softwaredependent, as a function of the image set and number of images, with model accuracies ranging between 0.2 and 3.8m in the best and worst scenario, respectively. Although some limitations derived from the generation of 3-D models from SVI were observed, this approach allowed us to obtain preliminary 3-D models of an area without on-field images, allowing extraction of the pre-failure topography that would not be available otherwise. [ABSTRACT FROM AUTHOR]

In June 2005, a series of major rockfall events completely wiped out the Bonatti Pillar located in the legendary Drus west face (Mont Blanc massif, France). Terrestrial lidar scans of the west face were acquired after this event, but no pre-event point cloud is available. Thus, in order to reconstruct the volume and the shape of the collapsed blocks, a 3-D model has been built using photogrammetry (structure-from-motion (SfM) algorithms) based on 30 pictures collected on the Web. All these pictures were taken between September 2003 and May 2005. We then reconstructed the shape and volume of the fallen compartment by comparing the SfM model with terrestrial lidar data acquired in October 2005 and November 2011. The volume is calculated to 292 680 m³ (±5.6 %). This result is close to the value previously assessed by Ravanel and Deline (2008) for this same rock avalanche (265 000 ± 10 000 m³). The difference between these two estimations can be explained by the rounded shape of the volume determined by photogrammetry, which may lead to a volume overestimation. However it is not excluded that the volume calculated by Ravanel and Deline (2008) is slightly underestimated, the thickness of the blocks having been assessed manually from historical photographs. [ABSTRACT FROM AUTHOR]

Analogue methods (AMs) predict local weather variables (predictands) such as precipitation by means of a statistical relationship with predictors at a synoptic scale. The analogy is generally assessed on gradients of geopotential heights first to sample days with a similar atmospheric circulation. Other predictors such as moisture variables can also be added in a successive level of analogy. The search for candidate situations similar to a given target day is usually undertaken by comparing the state of the atmosphere at fixed hours of the day for both the target day and the candidate analogues. This is a consequence of using standard daily precipitation time series, which are available over longer periods than sub-daily data. However, it is unlikely for the best analogy to occur at the exact same hour for the target and candidate situations. A better analogue situation may be found with a time shift of several hours since a better fit can occur at different times of the day. In order to assess the potential for finding better analogues at a different hour, a moving time window (MTW) has been introduced. The MTW resulted in a better analogy in terms of the atmospheric circulation and showed improved values of the analogy criterion on the entire distribution of the extracted analogue dates. The improvement was found to increase with the analogue rank due to an accumulation of better analogues in the selection. A seasonal effect has also been identified, with larger improvements shown in winter than in summer. This may be attributed to stronger diurnal cycles in summer that favour predictors taken at the same hour for the target and analogue days. The impact of the MTW on the precipitation prediction skill has been assessed by means of a sub-daily precipitation series transformed into moving 24 h totals at 12, 6, and 3 h time steps. The prediction skill was improved by the MTW, as was the reliability of the prediction. Moreover, the improvements were greater for days with heavy precipitation, which are generally related to more dynamic atmospheric situations in which the timing is more specific and for which fewer records are available in the meteorological archive. The improvements of the analogy criterion and the performance scores on precipitation were both found to be higher for MTWs with a smaller time step of 3 h. A 3 h MTW provides 8 times more candidate situations even though they are not fully independent. Since the MTW provides additional situations to the pool of possible analogues, it can be considered as an inflation of the meteorological archive. Because this technique is simple and easily applicable, it should be considered for several applications in different contexts, such as operational forecasting or climate-related studies. [ABSTRACT FROM AUTHOR]

We present an automated terrestrial laser scanning (ATLS) system with automatic near-real-time change detection processing. The ATLS system was tested on the Séchilienne landslide in France for a 6-week period with data collected at 30 min intervals. The purpose of developing the system was to fill the gap of high-temporal-resolution TLS monitoring studies of earth surface processes and to offer a cost-effective, light, portable alternative to ground-based interferometric synthetic aperture radar (GB-InSAR) deformation monitoring. During the study, we detected the flux of talus, displacement of the landslide and pre-failure deformation of discrete rockfall events. Additionally, we found the ATLS system to be an effective tool in monitoring landslide and rockfall processes despite missing points due to poor atmospheric conditions or rainfall. Furthermore, such a system has the potential to help us better understand a wide variety of slope processes at high levels of temporal detail. [ABSTRACT FROM AUTHOR]

Regional landslide assessments and mapping have been effectively pursued by research institutions, national and local governments, non-governmental organizations (NGOs), and different stakeholders for some time, and a wide range of methodologies and technologies have consequently been proposed. Land-use mapping and hazard event inventories are mostly created by remote-sensing data, subject to difficulties, such as accessibility and terrain, which need to be overcome. Likewise, landslide data acquisition for the field navigation can magnify the accuracy of databases and analysis. Open-source Web and mobile GIS tools can be used for improved ground-truthing of critical areas to improve the analysis of hazard patterns and triggering factors. This paper reviews the implementation and selected results of a secure mobile-map application called ROOMA (Rapid Offline--Online Mapping Application) for the rapid data collection of landslide hazard and risk. This prototype assists the quick creation of landslide inventory maps (LIMs) by collecting information on the type, feature, volume, date, and patterns of landslides using open-source Web-GIS technologies such as Leaflet maps, Cordova, GeoServer, PostgreSQL as the real DBMS (database management system), and PostGIS as its plug-in for spatial database management. This application comprises Leaflet maps coupled with satellite images as a base layer, drawing tools, geolocation (using GPS and the Internet), photo mapping, and event clustering. All the features and information are recorded into a GeoJSON text file in an offline version (Android) and subsequently uploaded to the online mode (using all browsers) with the availability of Internet. Finally, the events can be accessed and edited after approval by an administrator and then be visualized by the general public. [ABSTRACT FROM AUTHOR]

How do environmental risk systems function? is the main underlying question to be answered by students learning environmental risk. Under the framework of the Innovative Teaching project, an open-source, interactive and collaborative web-GIS application (RISKGIS) is developed for students in learning and understanding of environmental risk systems with a focus on geohazards and risk. The aim is for students to better understand and become familiarized with approaches used by experts as well as for teachers to better evaluate and monitor student learning, through a practical application with real case studies and hand-on exercises. To identify the possibility and applicability of the developed learning platform, a series of practical exercises is carried out with undergraduate and postgraduate students during the spring and autumn semesters of the environmental risk, and advanced risk and vulnerability courses of the University of Lausanne. A total of three exercises are conducted starting from the rapid risk calculation (individual) exercise to more complex risk management (individual and group) exercise with different case studies and functionalities of the learning platform. Depending on the exercises, students are asked to answer the test quiz, feedback questionnaires and group reports (if requested) through the Moodle platform to evaluate the performance of the students, exercises and the RISKGIS platform. Average feedback results from three different exercises revealed that students found the exercises useful and interesting, while a user satisfaction score of 7/10 and a system usability scale (SUS) of 64/100 is achieved, showing that several aspects of the RISKGIS learning platform could be further improved with suggestions and feedback of the students. [ABSTRACT FROM AUTHOR]

In June 2005, a series of major rockfall events completely wiped out the Bonatti Pillar located in the legendary Drus West face (Mont-Blanc massif, France). Terrestrial LiDAR scans of the face were acquired after this event but no pre-event point cloud is available. Thus, in order to reconstruct the volume and the shape of the collapsed blocks, a 3D model has been built using photogrammetry (SfM) based on 30 pictures collected on the Web. All these pictures were taken between September 2003 and May 2005. We then reconstructed the shape and volume of the fallen compartment by comparing the SfM model with terrestrial LiDAR data acquired in October 2005 and November 2011. The volume is calculated to 292'680 m³ (±5 %). This result is close to the value previously assessed by Ravanel and Deline (2008) for this same rock-avalanche (265'000 ± 10'000 m³). The difference between these two estimations can be explained by the rounded shape of the volume determined by photogrammetry, which may lead to a volume overestimation. However it is not excluded that the volume calculated by Ravanel and Deline (2008) is slightly underestimated, the thickness of the blocks having been assessed manually from historical photographs. [ABSTRACT FROM AUTHOR]

Regional landslide assessments and mapping have been effectively pursued by research institutions, national and local governments, NGOs and different stakeholders for some time; and a wide range of methodologies and technologies are proposed consequently. Land-use mapping and hazard event inventories are mostly created by remote sensing data, resulting in complications subject to accessibility and terrain. However, landslide data acquisition for the field navigation can magnify the accuracy of database and analysis. Analysing hazard patterns and triggering factors can take advantage of Open Source web and mobile GIS tools for an improved ground-truthing of critical areas. This paper reviews implementation of a secure mobile-map application called ROOMA (Rapid Offline-Online Mapping Application) for the fast data collection of landslide hazard and risk. This prototype assists for quick creation of landslide inventory maps by collecting information on the type, feature, volume, date and pattern of the landslide using Open Source web-GIS technologies for instance Leaflet maps, Cordova, GeoServer, Postgis and Postgres database. This application comprises of Leaflet map coupled with satellite images as base layer, drawing tools, geolocation (using GPS and Internet), photo mapping and events clustering. All the features and information are recorded into a Geojson file in an offline version (Android) and consequently uploaded to the online mode (using all browsers) with the availability of internet. Finally, the events can be accessed and edited after approval by an administrator and then be visualized by general public. ROOMA was tested for the collection of landslides in post-earthquake Nepal and can be applied as well for all other events and hazards such as floods, avalanches, etc. [ABSTRACT FROM AUTHOR]

Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter-early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope-channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow. [ABSTRACT FROM AUTHOR]

The southeastern side of Mont Blanc is constituted of high granitic peaks affected bydifferent degree of fracturing. In the last hundred years, two major ice-rock avalanche eventstook place on the Brenva Glacier involving volumes of more than 2×106 m3. In September2016, a volume of 35’000 m3 detached from the previous rock avalanche scar and wasdeposited on the higher part of the Brenva Glacier. This new event has pushed Aosta ValleyAutonomous Region authorities to investigate in more detail the "Sperone della Brenva" rockmass. Between July 2017 and October 2018, three Photogrammetric Points Clouds (PPCs)were generated using structure-from-motion techniques from hundreds of pictures takenduring helicopter flights. The structural analysis of PPCs enabled to identify four major fracture sets in the rockavalanche scar. By fitting planes deeply along these fractures, different potentiallyunstable volumes were calculated and several scenarios were defined. During autumn2017, deformation of the rock wall was also monitored with a ground-based InSARsystem. No significant mass movement was detected; nevertheless, three rockfallevents occurred between July 2017 and October 2018, indicating that some activityremains. Heliported infrared thermal images were also acquired in October 2018. Althoughthermal signatures are not simple to analyze at the rock face scale, thermograms show thatsome fractures are colder and residual ice areas display negative temperatures. Presence ofwater leaking on the rock wall is clearly visible on these images, suggesting that theinteraction between permafrost and melted water influence greatly the stability of the Speronedella Brenva. By combining all these observations, the scenarios have been ranked in hazard levels. Ifthe collapse of mid-volumes of about 1×105 m3 is rather likely within a short delay, thefailure probability is lower for larger volumes. However, due to global warming and annualsnow cover variations, the monitoring (measuring instruments and/or monitoring activity)needs to be continued in order to permanently re-evaluate the probability of failure of eachscenario. [ABSTRACT FROM AUTHOR]

Hyperspectral cameras are actually pushbroom line-scanner. For groundbased acquisitions, they require a motorized rotating platform and often a logistics (external batteries and computer) quite heavy for real fieldwork. In 2018, a new small and handy camera was proposed on the market, the Specim IQ. It covers visible and near infrared bands (400-1000 nm), with a spectral resolution of 7 nm (204 spectral bands), a spatial sampling of 512x512 pixels, for a total weight of 1.3 kg (+ a photo tripod). We proceeded to some tests on various rocks (granite, peridotite, metamorphic gneisses, limestone, marble and detritic rocks) in outdoor conditions. Spectralon plates were used for spectrum referencing. The goal of these preliminary experiments is to identify the potential of this device to distinguish rock types, surface weathering stages, and the limitations due to light conditions and incidence angles. [ABSTRACT FROM AUTHOR]

A very important issue in rockfall analysis is to evaluate the rate of rock surface erosion, which is a crucial index to indicate rockfall activities. Over the last 15 years, point clouds datasets for evaluating the rate of rock surface erosion and rock mass structure analysis were mainly acquired by LiDAR and Structure-from-Motion photogrammetry (SfM). More recently, new scanning equipments called GeoSLAM and Sense 3D, easy to carry because their small size/weight and mainly used for 3D reconstruction of object indoors, showed great potential to be applied to extract the topography of a rock outcrop. However, to date no detailed comparative study about the accuracy and density of point clouds acquired by LiDAR, SfM, GeosLAM and Sense 3D has been reported. By using these three last techniques, we first performed an indoor experiment to acquire three different point clouds of a small rectangular box (6.5×4.4×3.7 cm3) placed on a table. The preliminary results show that SfM and Sense 3D models have a higher resolution and point density than the one acquired with GeoSLAM. The second experiment performed outdoor to monitor fast erosion of a molassic rock wall of 3 m-high by 2 m-width using the four techniques. The aim of this work is to find the most suitable method to monitor in fine scale erosion and deformation of rock wall surface to study rock mass degradation. [ABSTRACT FROM AUTHOR]

This paper presents an overview of a historic case of a rock avalanche that was potentially induced by an earthquake in the area of Korbous Nothern East of Tunisia. This study is important because Tunisia suffers from the lack of historical events archive and of any previous detailed study about rockslides and landslides. We analyze here the morphological and seismotectonic settings that are considered as the key parameters for earthquake-induced rockslides analysis. Northern East of Tunisia is an active tectonic area (earthquakes, active faults, etc...) due to its seismotectonic settings in the context of the Africa-Eurasia plate boundary. The region of Korbous is affected by different slope mass movements types mainly triggered by rainfall as it has been the case in fall 2018. But earthquakes acting as rockslide-trigger have not been considered yet. The cliff of Korbous, situated in the eastern part of the Gulf of Tunis, is about 35km and 60km distance from the faults of Tunis and Utique, the two most important historical seismogenic faults in the region, which could be the cause of an earthquake-induced rockslide favored by local geological and morphological conditions. By using landscape analysis techniques combined with field observations and measurements, structural measurements (Angelier 1990) and aerial photos interpretation we i) identified the main joints orientation that confirmed the geology model of the cliff (the main scarp cracks orientation and failure surface) and ii) determined the initial localization of the source area, the volume and the propagation trajectory of the rockslide.By dating several samples from the quaternary sedimentary sequence at the foot of the slope associated with the rockslide deposit we could define the material ages and consequently the timing of related mass movement and corresponding seismic event. We found that most criteria of identification that mark a "typical earthquake-triggered landslides" described by Havenith and Storm (2018) and Havenith and Bourdeau (2010) are fulfilled in the case of Korbous rock avalanche. [ABSTRACT FROM AUTHOR]

In the field of rock mechanics, the characterization of discontinuity persistence and intact rock bridges is needed to define stability conditions of fractured rock masses. Although methods for mapping these structural features have improved in recent years, remote imagery detection of intact rock bridges has not yet been performed. In steep exfoliating cliffs, such as El Capitan in Yosemite Valley (California, USA), rockfalls mainly occur along exfoliation joints (i.e., surface-parallel fractures separating exfoliation sheets) (Collins and Stock, 2016; Collins et al., 2018; Stock et al., 2018). Thus, we focused on the detection of rock bridges responsible for the stability of partially detached exfoliation sheets. We conducted InfraRed Thermography (IRT) monitoring, in conjunction with Terrestrial Laser Scanning (TLS) surveying to characterize the stability of two well-delimited granitic exfoliation sheets. By examining the final phase of diurnal cooling of these flakes with IRT, we found that they always remain colder than the surrounding rock walls. We interpret this colder thermal signature as a result of the air circulation that envelops and cools the detached parts from the cliff. Detailed analysis of each thermal image also revealed that the temperature patterns are not homogeneous – warmer thermal anomalies are visible on the surface of both monitored flakes. We interpret these warmer areas as a sign of the possible presence of rock bridges that would conduct heat from the rock mass located behind the exfoliation sheets. The detection of rock bridges from our IRT analysis is supported by the results of 2-D thermal modeling. These simulations reproduced the observed thermal signatures and improved our understanding of the temperature differences detected in the rock bridge area. By draping IRT images on TLS meshes, we were then able to measure the geometry of the potential rock bridge surfaces and subsequently evaluate the exfoliation sheet stability conditions using fracture mechanics analysis. This study demonstrates that thermal imaging combined with high-resolution 3D topography have great potential for rock failure hazard assessment. [ABSTRACT FROM AUTHOR]