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Accurate rockfall modeling is crucial for evaluating rockfall hazards and requires consideration of several inputs data, including parameters that control boulder trajectories and source areas. Inaccurate definitions of source areas can lead to unrealistic representations of the rockfall process. In this study, we analyze how different approaches used to define source areas can affect the accuracy of rockfall modeling. The island of El Hierro (Canary Islands, Spain) is selected due to its geological and geomorphological characteristics, as well as the socio-economic importance of rockfalls on the island. To assess rockfall source areas, three different approaches were considered, ranging from situations with limited data availability to scenarios with many topographic, geological and geomorphological information. A morphometric firstly approach establishes a slope angle threshold above which block detachment zones are considered. For the second approach, we have employed a statistical method to identify rockfall source areas, using Empirical Cumulative Distribution Functions (ECDF) of slope angle values. The third method was a probabilistic modeling framework that applies a combination of multiple multivariate statistical classification models. These models use the mapped source areas as a dependent variable, as well as a set of thematic information as independent variables. The source area maps obtained from the three methods were used as inputs for a rockfall runout model, to establish a classification of rockfall susceptibility areas. One of the main outcome of the rockfall modeling simulations on El Hierro is the rockfall trajectory counts maps, showing areas prone to rockfalls. These maps indicate the probability of a given pixel being affected by a rockfall event. Two classification approaches were applied to generate the probabilistic susceptibility maps: unsupervised and supervised statistical methods by using distribution functions. The unsupervised classification only employs as input the raster map of the rockfall trajectory counts. In contrast, the supervised classification requires additional data on the areas already affected by rockfalls. Finally, six susceptibility maps are developed and compared to highlight the influence of source areas definition on the distribution of rockfall trajectories. [ABSTRACT FROM AUTHOR]

Within an international cooperation network (France, Spain and Portugal) involving researchers, first responders and civil protection authorities, a crisis exercise was held simultaneously in Mallorca and Ibiza (Balearic Islands, Spain). The objectives were to test crisis management procedures defined by operational actors, integrating new developed scientific tools related to landslides and rockfalls, as well as the internal relationship with the new created Technical Advisory Committee. The initiative included a training module for all stakeholders before the exercise explaining the scientific tools used for supporting the decision-making process during the exercise, as well as a field trip in the Tramuntana range in Mallorca to gain first-hand knowledge of the geological hazards threatening the region, mainly rockfalls. More than 70 people were involved in the training exercise, including researchers, civil protection, civil guard, municipalities, representants of the autonomous regions, local and regional crisis management managers from different French and Spanish entities, etc. At the end of the exercise, a joint analysis was made of the strengths and weaknesses found during the development of the exercise and propositions of improvements were made. Local and regional authorities concluded that, thanks to the exercise, they are better prepared to deal with georisks induced by extreme weather, mainly landslides and rockfalls. The scientific community understood the type of operational products they should develop for decision support during disaster risk crises. This experience emphasizes the need to create stronger links between the scientific community and civil protection stakeholders. [ABSTRACT FROM AUTHOR]

Featured Application: This review contribute to understand the mechanisms underlying the observed rockfall activity during and after a wildfire, to advance in the solutions and methods to address the study of the problem, and to assess the hazard during and after wildfire, and its impact on not only transportation infrastructure and urban areas, but also the population. The results will help the decision makers and emergencies authorities to evaluate the exposure of elements at risk, to define actions to reduce their vulnerability and to identify measures to mitigate damages and social impact. Understanding processes and conditions that lead to rockfalls during and after a wildfire in different geological contexts is crucial since this phenomenon is one of the major hazards in mountainous regions across Europe. Spain is one of the European countries with the highest rate of wildfires, and rockfalls cause high economic and social impact, with many fatalities every year. The increase of rockfalls during and after wildfires is connected with the merging of different factors, not only in the detached area but also in the propagation and potentially affected area. When wildfire occurred, many actions take place: changes in the mechanical conditions of the rocks, the loss of protective capacity from vegetation, the effect induced by firefighting activities and/or the impact by the high temperatures in the adopted protective measures. After the wildfire, there is an increase in frequency and intensity of rockfalls in the burned area, causing a major impact of rockfalls on not only road networks and built-up areas but also people living. Additionally, the removal of vegetation by wildfires causes an increase in the risk perception, related not only to detached blocks but also to the general appearance of the rock mass. In this review, the main factors that influence the occurrence of rockfalls after a wildfire are analyzed, and three actual case studies in Spain are presented to support the variety of conclusions obtained. [ABSTRACT FROM AUTHOR]

The island of Gran Canaria (Canary Islands, Spain) is characterized by a large variability of volcanic rocks reflecting its volcanic evolution. The geological map provided by Geological Survey of Spain at 1:25.000 scale shows more than 109 different lithologies and it is too complex for environmental and engineering purposes. This work presents a simplified geotechnical map with a small number of classes grouping up units with similar geotechnical behaviours. The lithologies were grouped using about 350 rock samples, collected in the seven major islands of the Archipelago. The geotechnical map was used to model rockfall hazard in the entire island of Gran Canaria, where rockfalls are an important threat. The rockfall map was validated with 128 rockfall events along the GC-200 road, located in the NW sector of Gran Canaria. About 96% of the events occurred along sections of the road where the number of expected trajectories is high or moderate. [ABSTRACT FROM AUTHOR]

Rockfalls are frequent and harmful phenomena occurring in mountain ranges, coastal cliffs, and slope cuts. Although several natural processes occur in their formation and triggering, rainfall is one of the most common causes. The prediction of rock failures is of social significance for civil protection purposes and can rely on the statistical analysis of past rainfall conditions that caused the failures. The paper describes the analysis of information on rainfall-induced rockfalls in Gran Canaria and Tenerife, Canary Islands (Spain). An analysis of the monthly rainfall versus the monthly distribution of rockfalls reveals that they are correlated for most of the year, except in summer, when other triggers act to induce collapses. National and regional catalogs with hourly and daily rainfall measurements are used to reconstruct the cumulated amount (E) and the duration (D) of the rainfall responsible for the rock failures. Adopting a consolidated statistical approach, new ED rainfall thresholds for possible rockfall occurrence and the associated uncertainties are calculated for the two test sites. As far as is known, this is the first attempt to predict this type of failure using the threshold approach. Using the rainfall information, a map of the mean annual rainfall is obtained for Gran Canaria and Tenerife, and it is used to assess the differences between the thresholds. The results of this study are expected to improve the ability to forecast rockfalls in the Canary Islands in view of implementing an early-warning system to mitigate the rockfall hazard and reduce the associated risk. [ABSTRACT FROM AUTHOR]

The Tramuntana range, in the northwestern sector of the island of Mallorca (Balearic Islands, Spain), is frequently affected by rockfalls which have caused significant damage, mainly along the road network. In this work, we present the procedure we have applied to calibrate and validate rockfall modelling in this region, using 103 cases of the available detailed rockfall inventory (630 rockfall events collected since the eighteenth century). We have exploited STONE (Guzzetti et al. 2002), a GIS-based rockfall simulation software which computes 2D and 3D rockfall trajectories starting from a DTM and maps of the dynamic rolling friction coefficient and of the normal and tangential energy restitution coefficients. The appropriate identification of these parameters determines the accuracy of the simulation. To calibrate them, we have selected 40 rockfalls along the range which include a wide variety of outcropping lithologies. Coefficients values have been changed in numerous attempts in order to select those where the extent and shape of the simulation matched the field mapping. Best results were summarized with the average statistical values for each parameter and for each geotechnical unit, determining that mode values represent more precisely the data. Initially, for the validation stage, 10 well-known rockfalls exploited in the calibration phase have been selected. Confidence tests have been applied to their modelling results taking into account not only the success but also the mistakes. The best accuracy is obtained when the rockfall has a preferential trajectory and worse results when the rockfall follows two or more trajectories. Additionally, the greater the rockfall runout length, the less precise the simulation is. We have further validated the calibrated parameters along the Ma-road (111 km), the main transportation corridor in the range, using 63 rockfall events that occurred during the past 18 years along the road. Of the rockfalls where source areas were properly identified, 81.5 % are well represented by STONE modelling, as the travel paths and the depositional areas are successfully ascertained. Results of the analysis have been used by the Road Maintenance Service of Mallorca to assess hazard and risk posed by rockfall at regional scale to design the road management plan. [ABSTRACT FROM AUTHOR]

An example of the combined use of UAV photogrammetry and rockfall numerical simulation is described. A case of fragmental rockfall occurred on 17 November 2018 in Cárcavos, a site located in the Spanish municipality of Ayna (Albacete). The event caused a great social alarm as some infrastructure was affected. By using Unmanned Aerial Vehicle (UAV) photogrammetry, a high-resolution 3D model has been generated from point cloud data, and distribution and size of the fragmented rocks (more than 600 boulders) determined. The analysis has been performed through numerical simulations to: (1) reproduce the paths followed by the real blocks; and (2) estimate the speed and energy of the blocks, together with their heights, impacts and stopping points. Accordingly, source areas have been identified, including the potential source areas and unstable blocks on the slope. In addition, the exposed elements at risk (buildings, facilities, infrastructures, etc.) have been identified, and the effectiveness of mitigation measures against future events evaluated. [ABSTRACT FROM AUTHOR]

Modelling rockfall phenomena is complex and requires various inputs, including an accurate location of the source areas. Source areas are controlled by geomorphological, geological, or other geo-environmental factors and may largely influence the results of the modelling. In the Canary Islands, rockfalls are extremely common and pose a major threat to society, costing lives, disrupting infrastructure, and destroying livelihoods. In 2011, the volcanic event on the island of El Hierro triggered numerous rockfalls that affected strategic infrastructures, with a substantial impact on the local population. During the emergency, the efforts performed to map the source areas and to model the rockfalls in the considerably steep landscape characterising the island were not trivial. To better identify the rockfall source areas, we propose a probabilistic modelling framework that applies a combination of multiple statistical models using the source area locations mapped in the field as the dependent variable and a set of thematic data as independent variables. The models use as input morphometric parameters derived from the Digital Elevation Model and lithological data as an expression of the mechanical behaviour of the rocks. The analysis of different training and validation scenarios allowed us to test the model sensitivity to the input data, select the optimal model training configuration, and evaluate the model applicability outside the training areas. The final map obtained from the model for the entire island of El Hierro provides the probability of a given location being a potential source area and can be used as the input for rockfall runout simulation modelling. • Identification of source areas is problematic and a key step influencing the result of rockfall simulation and modelling. • An ensemble of multivariate statistical probabilistic models is proposed for the identification of rockfall source areas. • The proposed approach provides reliable regional distribution of source areas without extensive field surveys. • The output maps may improve rockfall susceptibility zonation, providing an objective identification of source areas. [ABSTRACT FROM AUTHOR]

In recent years, there was an increasing number of studies focusing on rockfalls due to their impacts on social and sustainable development. This work carries out a three-dimensional (3D) simulation of rockfalls at a cultural heritage site nearby the village of Cortes de Pallás (Valencian Community, East Spain). The simulation is based on data collected previously, during an emergency declaration due to the occurrence of a considerable rockfall (7980 m3) on the southern bank of the Cortes de Pallás reservoir, on 6 April 2015. The hydroelectric power plant was damaged, and the main access road to the village of Cortes de Pallás was blocked for eight months. The predominant discontinuities of the rock mass were analyzed by means of the application of structure from motion (SfM) photogrammetry techniques to the set of images taken by remotely piloted aircraft systems (RPAS). The average size of the block was determined as 3.2 m in diameter and 17.6 m3 in volume. Additionally, a digital elevation model (DEM) was generated from an aerial laser scanning (ALS)-derived point cloud using a 1 × 1 grid. These data were implemented in RocPro3D software, obtaining the distances traveled by the blocks detached from different source areas at a cultural heritage site located near the rockfall event, which presents the same geological context. The simulation presented herein shows aggravating circumstances that endanger the cultural heritage area, with higher rockfall hazards than previous official studies (1991) displayed. [ABSTRACT FROM AUTHOR]