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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]

Defining the relationship between volume and return period is critical when estimating the risk of rockfalls and/or rock avalanche, especially during continued global warming at high altitudes that threatens rock wall stability. Characterizing the volume-frequency relationship based on historical datasets is, however, limited by observation and quantification biases, which have not received enough attention. Here, to monitor recent activities for the Brenva Spur (Mont-Blanc massif, Italy) that is also a rock avalanche scar and estimate the return period of future rock failures based on the volume-frequency relationship (and the corresponding uncertainty), a structure-from-motion photogrammetric survey was conducted from 2017 to 2021. 39 rockfall sources with volumes ranging from 11 to 13,250 m3 were identified within the scar. The total failure volume is 22,438 m3, with an associated erosion rate of 15.5 mm/year, indicating very active morphodynamics possibly linked to the permafrost evolution in the spur. The volumes were characterized by a negative power-law that fits significant two events in 2016 (3.4 × 104 m3) and one in 1997 (2.0 × 106 m3) remarkably well, and the randomness of the fit was evaluated by a Monte Carlo approach. 7 potential failure scenarios ranging from 3.1 × 104 m3 (S 1) to 4.8 × 106 m3 (S 7) were defined according to a structural analysis and the sloping local base level concept. Their extrapolated return periods derived by the power-law fit indicate a longer return period for the maximum failure scenario than for the smaller scenarios. S 1 has a 50% chance of occurring every 3 years, while S 7 has a 50% chance of occurring every 31 years. Though the median return period of S 7 is 31 years, the 95% and 68.2% confidence intervals range from 8 to 399 years and 14 to 93 years, respectively, which reflects a high level of uncertainty but is realistic when considering global warming, progressive rock failure, etc. In addition to characterizing recent rock failure activities in high mountains, this study offers a preliminary examination of the return periods of some extreme scenarios and provides primary data for risk management in mountainous areas that are very sensitive to global warming. • Updated rock failure database by helicopter based SfM photogrammetry survey for Brenva Spur. • Detailed rockfall sources analysis linking geo-structures on the Brenva avalanche scar. • Extreme failure scenarios definition by discontinuity characterization and the SLBL concept. • Failure scenario return period estimation by volume-frequency relationship considering the uncertainties. [ABSTRACT FROM AUTHOR]

In this work an overview of the potential rock fall source areas and propagation assessment in the Province of Potenza territory has been presented. The rock fall process is characterized by two steps: the detachment of blocks and subsequently their propagation along the slope. The adopted methodology, used for the first time in the study area, and the software Histofit and FlowR have been very useful tools for the preliminary assessment of rock fall susceptibility at a regional scale, in particular because they have required low data of the study area. Only the DEM may be sufficient together with an appropriate choice of the input parameters and algorithms, that is to say: calculation method, directions algorithm, inertial algorithm and friction loss function. The output of the model is a map of the rock fall source areas, the propagation probabilities and the propagation kinetic energy. The results show that the adopted methodology is successful for the identification of rock fall source areas at a regional scale and the propagation probability obtaining an interesting rock fall susceptibility map. [ABSTRACT FROM AUTHOR]

Process-based rockfall simulation models attempt to better emulate rockfall dynamics to different degrees. As no model is perfect, their development is often accompanied and validated by the valuable collection of rockfall databases covering a range of site geometries, rock masses, velocities, and related energies that the models are designed for. Additionally, such rockfall data can serve as a base for assessing the model's sensitivity to different parameters, evaluating their predictability and helping calibrate the model's parameters from back calculation and analyses. As the involved rock volumes/masses increase, the complexity of conducting field-test experiments to build up rockfall databases increases to a point where such experiments become impracticable. To the author's knowledge, none have reconstructed rockfall data in 3D from real events involving block fragments of approximately 500 metric tons. A back analysis of the 2015 Mel de la Niva rockfall event is performed in this paper, contributing to a novel documentation in terms of kinetic energy values, bounce heights, velocities, and 3D lateral deviations of these rare events involving block fragments of approximately 200 m3. Rockfall simulations are then performed on a "per-impact" basis to illustrate how the reconstructed data from the site can be used to validate results from simulation models. [ABSTRACT FROM AUTHOR]

Rockfall simulations are often performed at various levels of detail depending on the required safety margins of rockfall-hazard-related assessments. As a pseudo benchmark, the simulation results from different models can be put side-by-side and compared with reconstructed rockfall trajectories, and mapped deposited block fragments from real events. This allows for assessing the objectivity, predictability, and sensitivity of the models. For this exercise, mapped data of past events from the Mel de la Niva site are used in this paper for a qualitative comparison with simulation results obtained from early calibration stages of the Flow-R 2.0.9, Rockyfor3D 5.2.15 and RAMMS::ROCKFALL 1.6.70 software. The large block fragments, reaching hundreds of megajoules during their fall, greatly exceed the rockfall energies of the empirical databases used for the development of most rockfall models. The comparison for this challenging site shows that the models could be improved and that combining the use of software programs with different behaviors could be a workaround in the interim. The findings also highlight the inconvenient importance of calibrating the simulations on a per-site basis from onsite observations. To complement this process, a back calculation tool is briefly described and provided. This work also emphasizes the need to better understand rockfall dynamics to help improve rebound models. [ABSTRACT FROM AUTHOR]

Based on a previous risk calculation study conducted along a road corridor, risk is recalculated using a stochastic simulation by introducing variability into most of the parameters in the risk equation. This leads to an exceedance curve comparable to those of catastrophe models. This approach introduces uncertainty into the risk calculation in a simple way, and it can be used for poorly documented cases to compensate for a lack of data. This approach tends to minimize risk or question risk calculations. [ABSTRACT FROM AUTHOR]

We present a long-term spatio-temporal analysis of rock slope evolution using a Terrestrial LiDAR aiming to improve our understanding of the link between pre-failure deformation and the spatial prediction of rockfalls. We monitored the pilot study area located at the Puigcercós cliff (Catalonia, Spain) over a period of 1,705 days and detected the deformation of nine different cliff regions together with a high rockfall activity. An exact match was observed between the progressively deformed areas and the regions recently affected by three of the highest magnitude rockfall events, demonstrating a causal relationship between pre-failure deformation and rockfall occurrence. These findings allowed us to make a forward spatial prediction of future failures, hypothesizing a high probability of failure in the six remaining regions. We observed an exponential acceleration of the deformation close to failure, in accordance with tertiary creep theory. However, the temporal analysis of the deformed areas showed a complex and variable behavior, so no exact prediction of the date of failure can yet be made. Our findings have broadened our understanding of the pre-failure behavior of rockfalls and have clear implications for the future implementation of early warning systems. [ABSTRACT FROM AUTHOR]

Numerous 3D rockfall simulation models use coarse gridded digital terrain model (DTM raster) as their topography input. Artificial surface roughness is often added to overcome the loss of details that occurs during the gridding process. Together with the use of sensitive energy damping parameters, they provide great freedom to the user at the expense of the objectivity of the method. To quantify and limit the range of such artificial values, we developed an impact-detection algorithm that can be used to extract the perceived surface roughness from detailed terrain samples in relation to the size of the impacting rocks. The algorithm can also be combined with a rebound model to perform rockfall simulations directly on detailed 3D point clouds. The abilities of the algorithm are demonstrated by objectively extracting different perceived surface roughnesses from detailed terrain samples and by simulating rockfalls on detailed terrain models as proof of concept. The results produced are also compared to that of rockfall simulation software CRSP 4, RocFall 8 and Rockyfor3D 5.2.15 as validation. Although differences were observed, the validation shows that the algorithm can produce similar results. With the presented approach not being limited to coarse terrain models, the need for adding artificial terrain roughness or for adjusting sensitive damping parameters on a per-site basis is reduced, thereby limiting the related biases and subjectivity. [ABSTRACT FROM AUTHOR]

Large slope collapses have been known to trigger extreme rushes of air loaded with projectiles (airblasts) capable of causing destruction and fatalities far beyond run-out of the rock mass. An appraisal of the likelihood of a destructive airblast should be a component of landslide risk assessments. Yet there is an absence of risk studies directly examining landslide-related airblasts. In this work we back-analyze an unreported airblast in the Sikkim Himalayas (India) and several other airblasts documented around the world. We explore the conditions a large slope collapse should meet to trigger a significant airblast, and we establish a semiempirical relationship linking the potential energy in a collapse with airborne trajectory and the extent of the related airblast. The collapse of thousands or millions of cubic meters falling from a significant height results in a sudden release of energy (1011J to 1013J) and a high degree of comminution of rocks, causing a violent displacement of air. Average wind speeds of airblasts following impacts with airborne trajectory can be double the speed of rock avalanches. The size of the damage zone depends on the potential energy of the falling rock mass and can be amplified or reduced depending on how confined the valley is where the airblast occurs. [ABSTRACT FROM AUTHOR]

To manage rockfall hazards, it is important to correctly estimate the reach distances and velocities of falling rock blocks. To do so, it is often needed to perform 3D rockfall simulations. However, finding the right set of parameters is often done subjectively given the lack of empirical 3D data to finetune the runouts and more generally the simulation models. However, during the last years, several 3D rockfall experiments has been performed to overcome this problem. Last autumn (2018), we joined our efforts to work on a larger rockfall experiment and improve a 3D rockfall database while benefiting from the knowledge and diversity of the collectivity. That time, commercial (MSR Electronics GmbH) and custom-made data loggers, accelerometers and gyroscopes were embedded in some of the launched blocks and a dense seismic network was deployed. Highspeed 4k and HD cameras were used in combination with different telephoto lenses from different locations on the ground and in the air to visually reconstruct the 3D trajectories. A highly detailed (many points per cm2) 3D point cloud terrain model was also acquired with terrestrial laser scanner (TLS), mobile TLS and UAV photogrammetry.In this presentation, the aspects of observed dynamics from the rockfall experiments that applies to rockfall simulations are detailed. An emphasis is made to the relation in between the impact angle, deviation that happen after an impact and velocity changes. Examples of how angles are strongly affected by the size of the particle and the encountered terrain surface roughness are given. In parallel, the compromises that we have made to allow our adapted simulation model to run on highly detailed terrain model while keeping a decent modeling speed are discussed.Also, the geometric approaches on point cloud and raster terrain models allowing the small particles to get caught into the surface roughness while letting the large ones travel further, like it is usually observed in scree slope, are explained with examples. They both consist at finding the "perceived" surface orientation by the block at impact instead of using the terrain local "slope and aspect" orientations. On raster, this is done by calculating a buffer over and around the terrain corresponding to the radius of the block. On the terrain, this translate into geometrically displacing the particle in contact over the surface while filling in the asperities that are too small to be reached. The same is performed with point cloud, but the approach is slightly different. It consists of finding where on the block the contact happens at impact. Then drawing a normed vector from this point toward the center of mass of the block. This vector is then used as the "perceived" normal to the ground at impact.The recently tuned rockfall model is finally applied to reconstruct previous real punctual natural and experimental rockfall events on several sites. It is interesting to see how few parameters must be adjusted with these combinations of approaches to get corresponding runouts. This restrains the biases associated with the subjectivity of choosing the right parameters. [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]

Rockfall causes a large number of accidents and fatalities in steep environments. A realistic quantification of rockfall risk is thus crucial for an effective prevention of damages and loss of lives. The estimation of rockfall and block volumes for different return periods thereby remains a major challenge. In this paper, we present a straightforward rockfall frequency model (RFM: Rockfall Frequency Model) and its application at 8 different sites at 7 locations in the Swiss Alps. The RFM assumes that the magnitude-frequency relationships of rockfall events and blocks follow a power law. The parameters of this distribution are estimated based on a simple classification of rock structures and on field inventories. Beside the block volume frequency, which is very sensitive to the consideration of large rockfall events, the frequency of rockfalls with at least one block with a minimum volume, is determined. The block size distributions measured in this study were well captured by power laws. The rockfall and block volumes calculated with the RFM were generally slightly higher than the scenarios of the official hazard assessments. The uncertainty analysis, however, revealed a high variability of the release scenarios with respect to the parameters of the RFM, increasing with the return period. Both, the rockfall volumes and the block volumes, are particularly sensitive to the estimated exponent of the power law distribution of the rockfall events. Nevertheless, the proposed RFM provides an objective and transparent approach to derive magnitude-frequency relationships of rockfall events and individual blocks even if historical inventories are missing or insufficient and is thus a promising alternative to merely expert-based approaches. • A straightforward rockfall frequency model allows for an objective estimation of rockfall and block release frequencies. • Block size distributions measured in the field were well fitted by power laws. • The uncertainty in the calculated release scenarios increases with the return period. [ABSTRACT FROM AUTHOR]

Integrated in a wide research assessing destabilizing and triggering factors to model cliff dynamic along the Dieppe's shoreline in High Normandy, this study aims at testing boat-based mobile LiDAR capabilities by scanning 3D point clouds of the unstable coastal cliffs. Two acquisition campaigns were performed in September 2012 and September 2013, scanning (1) a 30-km-long shoreline and (2) the same test cliffs in different environmental conditions and device settings. The potentials of collected data for 3D modelling, change detection and landslide monitoring were afterward assessed. By scanning during favourable meteorological and marine conditions and close to the coast, mobile LiDAR devices are able to quickly scan a long shoreline with median point spacing up to 10 cm. The acquired data are then sufficiently detailed to map geomorphological features smaller than 0.5 m. Furthermore, our capability to detect rockfalls and erosion deposits (>m) is confirmed, since using the classical approach of computing differences between sequential acquisitions reveals many cliff collapses between Pourville and Quiberville and only sparse changes between Dieppe and Belleville-sur-Mer. These different change rates result from different rockfall susceptibilities. Finally, we also confirmed the capability of the boat-based mobile LiDAR technique to monitor single large changes, characterizing the Dieppe landslide geometry with two main active scarps, retrogression up to 40 m and about 100,000 m of eroded materials. [ABSTRACT FROM AUTHOR]

There is an increasing need for quantitative rockfall hazard and risk assessment that requires a precise definition of the terms and concepts used for this particular type of landslide. This paper suggests using terms that appear to be the most logic and explicit as possible and describes methods to derive some of the main hazards and risk descriptors. The terms and concepts presented concern the rockfall process (failure, propagation, fragmentation, modelling) and the hazard and risk descriptors, distinguishing the cases of localized and diffuse hazards. For a localized hazard, the failure probability of the considered rock compartment in a given period of time has to be assessed, and the probability for a given element at risk to be impacted with a given energy must be derived combining the failure probability, the reach probability, and the exposure of the element. For a diffuse hazard that is characterized by a failure frequency, the number of rockfalls reaching the element at risk per unit of time and with a given energy (passage frequency) can be derived. This frequency is relevant for risk assessment when the element at risk can be damaged several times. If it is not replaced, the probability that it is impacted by at least one rockfall is more relevant. [ABSTRACT FROM AUTHOR]

The use of 3D point clouds to improve the understanding of natural phenomena is currently applied in natural hazard investigations, including the quantification of rockfall activity. However, 3D point cloud treatment is typically accomplished using nondedicated (and not optimal) software. To fill this gap, we present an open-source, specific rockfall package in an object-oriented toolbox developed in the MATLAB® environment. The proposed package offers a complete and semiautomatic 3D solution that spans from extraction to identification and volume estimations of rockfall sources using state-of-the-art methods and newly implemented algorithms. To illustrate the capabilities of this package, we acquired a series of high-quality point clouds in a pilot study area referred to as the La Cornalle cliff (West Switzerland), obtained robust volume estimations at different volumetric scales, and derived rockfall magnitude–frequency distributions, which assisted in the assessment of rockfall activity and long-term erosion rates. An outcome of the case study shows the influence of the volume computation on the magnitude–frequency distribution and ensuing erosion process interpretation. [ABSTRACT FROM AUTHOR]

Since the end of the Little Ice Age, the west face of the Drus (Mont Blanc massif, France) has been affected by a retrogressive erosion dynamic marked by large rockfall events. From the 1950s onwards, the rock failure frequency gradually increased until the large rockfall event (292,680 m3) of June 2005, which made the Bonatti Pillar disappear. Aiming to characterize the rock failure activity following this major event, which may be related to permafrost warming, the granitic rock face was scanned each autumn between October 2005 and September 2016 using medium- and long-range terrestrial laser scanners. All the point clouds were successively compared to establish a rockfall source inventory and determine a volume-frequency relationship. Eleven years of monitoring revealed a phase of rock failure activity decay until September 2008, a destabilization phase between September 2008 and November 2011, and a new phase of rock failure activity decay from November 2011 to September 2016. The destabilization phase was marked by three major rockfall events covering a total volume of 61,494 m3, resulting in the progressive collapse of a new pillar located in the northern part of the June 2005 rockfall scar. In the same way as for the Bonatti Pillar, rock failure instability propagated upward with increasing volumes. In addition to these major events, 304 rockfall sources ranging from 0.002 to 476 m3 were detected between 2005 and 2016. The temporal evolution of rock failure activity reveals that after a major event, the number of rockfall sources and the eroded volume both follow a rapid decrease. The rock failure activity is characterized by an exponential decay during the period following the major event and by a power-law decay for the eroded volume. The power law describing the distribution of the source volumes detected between 2005 and 2016 indicates an exponent of 0.48 and an average rock failure activity larger of more than six events larger than 1 m3 per year. Over the 1905–2016 period, a total of 426,611 m3 of rock collapsed from the Drus west face, indicating a very high rock wall retreat rate of 14.4 mm year−1 over a surface of 266,700 m2. Averaged over a time window of 1000 years, the long-term retreat rate derived from the frequency density integration of rock failure volumes is 2.9 mm year−1. Despite difficulty in accessing and monitoring the site, our study demonstrates that long-term surveys of high-elevation rock faces are possible and provide valuable information that helps improve our understanding of landscape evolution in mountainous settings subject to permafrost warming. [ABSTRACT FROM AUTHOR]

Rockfalls and rockslides are often dominant geomorphic processes in steep bedrock landscapes, but documenting their occurrence can be challenging, requiring frequent monitoring and well resolved spatial data. Repeat application of remote sensing methods such as Terrestrial Laser Scanning (TLS) and Structure-from-Motion (SfM) photogrammetry can detect even very small rockfalls, but typically these acquisitions span only years and may not record rockfall activity representative of longer-term rates of cliff erosion. Inventory databases can extend rockfall records, but are commonly incomplete and prone to observation bias. We employed TLS and SfM on two adjacent cliffs (El Capitan and Middle Brother) in Yosemite Valley, integrating semi-annual data collections from 2010 to 2017 with "historical" (archival) SfM models derived from oblique photographs taken in 1976. Comparing the 1976 SfM models against more recent data allows for more accurate and precise rockfall detection and volume measurement over a 40-year period. Change detection indicates that 235 rockfalls occurred from the two cliffs, more than twice as many events as are recorded in Yosemite's inventory database. Although individual rockfall volumes reported in the inventory database vary from those measured by SfM-TLS, reported cumulative volumes are similar to measured volumes, likely because the large-volume events that account for most of the cumulative volume tend to be widely observed and well-documented. Volume-frequency relationships indicate that the cliffs erode predominantly by less frequent, larger-volume rockfalls, at rates of 0.9 to 1.7 mm/yr. Our study demonstrates how integrated SfM and TLS measurements, especially utilizing SfM models derived from historical imagery, allow detection and quantification of rockfalls spanning several decades, complementing and improving inventory databases, informing rockfall hazard assessment, and providing longer-term rates of cliff erosion. • 1976's photographs yielded high-resolution models of two cliffs in Yosemite Valley. • "Historical" models were compared to terrestrial lidar data acquired in 2010/2016. • 235 rockfalls were detected from the two monitored cliffs over a 40-year period. • Both cliffs experienced twice as many rockfalls as are recorded in the database. • Rockfall volume-frequency relationships indicate erosion rates of 0.9 to 1.7 mm/yr. [ABSTRACT FROM AUTHOR]

As part of the promotion of the outdoor climbing sport, this project consists of monitoring the risk of rockfall on climbing walls of the old limestone quarry of St-Triphon (Switzerland). This specific study is the result of a comparison of 3D topographic survey of the North wall and the analysis of instability mechanisms. A first LiDAR acquisition and structural analysis of the whole quarry were performed in March 2010. In March 2017, a second 3D topographic acquisition was performed by drone and Structure from motion (Sfm) and by LiDAR.The comparison of the two 3D topographic datasets allowed an identification of the fallen and intentionally removed blocks from the North climbing wall. 15 blocks have been identified and their volumes have been estimated.In the inventory, intentionally removed blocks are distinguished from those that felt spontaneously. In 2010, 9 major blocks were identified as potentially unstable. For all types of blocks, an estimation of their volume has been plotted on a magnitude-frequency graph and their distributions fitted by power laws.For all considered "removed block", we can expect that in average:• A block of volume of at least of 0.05 m3 will fall each year. • A block whose volume is greater or equal to 0.4 m3 will fall every 5 year.• A block of 50 m3 each 10 years.For other types of the block, interpreted as naturally fallen, we can expect a event of a volume greater or equal to 0.06 m3 each year. For potentially unstable blocks not yet fallen, we can expect a rockfall of 0.04 m3 each year, 0.3 m3 each 5 year and 30 m3 every 10 years.Base on magnitude/frequency analysis, following recommendations can be made. Blocks with volume less than 0.05 m3, must be removed in the year. Blocks with volumes between 0.05 and 0.3 m3 have to be removed every 5 years. All these blocks are relatively small volumes, so they can be manually removed (work on rope and with a crowbar). Blocks with volumes greater than 0.3 m3 have a low probability of falling in a near future, but are considered as dangerous on a medium-term. These could be purged by blasting or nailed in order to significantly increase their stability. [ABSTRACT FROM AUTHOR]