Jordi Corominas

Rockfalls are the slope instability processes that cause the greatest number of victims in Spain, as well as considerable economic losses. This paper quantifies the impact of fatal rockfalls obtained from the documentary collection, mainly written press. We compiled 1,118 events that occurred between 1803 and 2021 and caused casualties (1,550 deaths and around 2,184 injuries). From this set, we analyzed the seasonal distribution and multiannual evolution of 1,018 rockfalls events for the period 1872–2021 (150 years) in which the daily written press was available. The inventoried cases were divided according to the context in which they occurred: dwellings and villages, quarries and excavations, railways, roads and outdoor activities (mountain trails and coastal areas). Diverging trends are observed. While the consequences and risk have decreased as stabilization and prevention actions accumulate around threatened dwellings, quarries and railroads, the number of fatal incidents has increased on roads and in natural spaces. This is due to the increase in roads and traffic, and especially, the greater presence of people in the natural environment (increased exposure). We present a first quantitative estimate of the investments made by administrations to stabilize artificial cuts and natural cliffs in order to reduce the risk of rockfalls.

The elements of the physical environment have long been the object of naming. Indeed, an area’s first inhabitants would have given names to places to satisfy their social need to locate themselves spatially and many of these names have been preserved until the present day. As such, place names reveal aspects of the landscape observed in the distant past by our ancestors. One such element of the physical environment is its geological features. Toponymy, in the case of the study of transparent place names in relation to aspects of the immediate terrain, is a useful tool in geology both for producing thematic maps and for locating and studying such features as caves, landslides and metal ores. At the same time, geology can help understand and clarify less transparent toponymic meanings and shed light on etymological hypotheses based on linguistic interpretations. This approach, supported by the compilation of background and comparative physiographic analyses of the geological characteristics of locations with similar place names, has considerable potential for identifying, recognizing and unravelling the origins of the names of many places. This paper presents a number of reciprocities identified between place names and their geology and assesses them as a tool for the recognition of physical features of the landscape.

El reconocimiento geomorfológico de sectores afectados por fenómenos geológicos peligrosos no siempre es una tarea fácil, especialmente cuando la suavización de formas, por procesos de regulación de laderas, actúa y desdibuja los rasgos más característicos que ayudan a su identificación. Al margen de esta dificultad, las consecuencias de estos fenómenos –en especial, si son de intensidad considerable o recurrentes– suelen permanecer en la memoria de los habitantes del territorio en cuestión durante generaciones. Y, en ocasiones, el recuerdo queda fosilizado a través de la denominación del paraje; es decir: el topónimo. La información aportada por estos nombres propios es un dato más en la elaboración de cartografías geológicas, estudios temáticos de riesgo, etc. En este artículo presentamos ejemplos de series de topónimos relacionados con los riesgos geológicos localizados principalmente en un sector del Alto Pirineo catalán y andorrano. También explicamos la metodología, basada en el análisis fisiográfico-toponímico comparado, utilizada en la identificación e interpretación de aquellos nombres que son opacos, incluso a la luz de la lingüística.

Significant effort has been devoted during the last few decades to the development of methodologies for landslide hazard and risk assessment. All of this work requires harmonization of the methodologies and terminology to facilitate communication within the landslide community, as well as with stakeholders and researchers from other disciplines. Currently, glossaries, and methodological recommendations exist for preparing landslide hazard and risk studies. Nevertheless, there is still debate on the usage of some terms and their implementation in practice.In 2016, the IAEG commission C-37 established a working group with the objective of preparing a standard multilingual glossary of landslide hazard and risk terms. The glossary aims for the international harmonization of the terms and definitions with those used in associated disciplines (e.g., seismology, hydrology) while considering landslides specifically. The glossary is based on previously published glossaries, including those prepared by ISSMGE TC32, FedIGS, JTC1, and UNISDR. This article presents comments on the meaning of some of the terms that have required further discussion. The English version of the glossary is also included.

Fragmentation is a common feature of rockfall that exerts a strong control on the trajectories of the generated blocks, the impact energies, and the runout. In this paper, we present a set of four real-scale rockfall tests aimed at studying the fragmentation of the rocky blocks, from the global design of the field procedure to the data analysis and the main results. A total of 124 limestone, dacite, or granite blocks ranging between 0.2 and 5 m³ were dropped from different heights (8.5 to 23.6 m) onto four slopes with different shapes (single or double bench) and slope angles (42º to 71º). The characteristics of the blocks, in particular the size, surface texture and joint condition, were measured before the drops. The trajectories of the blocks and both the initial and the impact velocities were tracked and recorded by means of three high-speed video cameras. A total of 200 block-to-ground impacts have been studied. On average, 40% of the blocks broke upon impact on the slope or on the ground, making it necessary to measure the fragments. The initial and final sizes of the blocks/fragments were measured by hand with tape, though photogrammetric techniques (UAV and terrestrial) were also used for comparison purposes. The information gathered during the field tests provides a deep insight into the fragmentation processes. On the one hand, the high-resolution slow-motion videos help to describe when and how the block breakage takes place and the spatial distribution of the pieces. On the other hand, it is possible to compute the block trajectories, the velocities, and the energy losses using videogrammetry. The results include, for instance, a block average fragmentation of 54% and 14% for the limestone and granitoids, respectively; the systematic inventory of the size fragments, which may be used for fitting the power law distributions; and after each breakage, the total angle of aperture occupied by the fragments has been measured, with values in the range 25º–145º. To figure out the different behavior of the blocks in terms of breakage/no breakage, each block-to-ground impact has been characterized with a set of parameters describing the energy level, the robustness of the substrate, and the configuration of the block contact at the impact point, among others. All these terms are combined in a function F, which is used to adjust the field data. The adjustment has been carried out, first, for the whole 200 events and later for a subset of them. The procedure and the results are described in the paper. Although the discrimination capability of F is moderately satisfactory, it is very sensitive to the test site and setup. It must be highlighted that these field tests are a unique source of data to adjust the parameters of the numerical simulation models in use for rockfall studies and risk mitigation, especially when fragmentation during the propagation is considered.

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.

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 to use terms that appear to be the more logic and explicit as possible, and describes methods to derive some of the main hazard 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 hazards and diffused 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 propagation 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 (reach frequency) can be derived. However, when the element at risk is not replaced or repaired, the probability that it is impacted by at least one rockfall must be considered.

Works carried out to monitor the displacements of the Vallcebre landslide (Pyrenees range, NE of Spain) since 1987 are presented. The landslide, which extends over an area of about 0.8 km² and affects more than 20 × 10⁶ m³, has experienced displacements of up to one meter per year in some points and periods. It has been periodically monitored since 1987, using a wide range of surface and in-hole techniques: triangulation with theodolite, Terrestrial Photogrammetry, Electronic Distance Measurement, GNSS-GPS, inclinometers, wire extensometers, piezometers, DInSAR (satellite) and GBSAR (terrestrial). The results obtained using new techniques are compared with those obtained with GNSS-GPS and a wire extensometer, and checked against fixed stable points. From this comparison, we conclude that even though wire extensometers and inclinometers may have the highest precision, in practice, all systems play potentially valuable roles in providing meaningful data for monitoring at different study stages. In the near future, we envisage the installation of a Distributed Fiber Optic array to monitor the risk with a certain space and time continuity. After the evaluation of the precision and advantages of the different methods, the complementary use of some of them is strongly recommended.

Real-scale fragmentation tests provide high quality data in order to study the fragmentation pattern of rock blocks. In the tests carried out, the initial rock mass, in terms of both volume and shape, was reconstructed by means of 3D photogrammetry. The fragments size distribution of the bocks tested was measured by hand using a tape. The drop tests were performed in four different sites, releasing a total of 124 blocks and measuring 2907 fragments. The obtained fragment size distributions may be well fitted using power laws. The survival rate (Sr), which is the proportion of remaining block shows a wide range of values. Observing the fragment distribution, two parameters are needed to characterize the fragmentation: the number of fragments produced and Sr. The intensity of the fragmentation is expressed by the exponent of the fitted power laws. Although the results are highly variable and show a stochastic behavior of the fragmentation, we have identified different patterns that reflect some local test conditions.