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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]

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]

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]