Aproximación probabilística al número y tamaño de bloques en desprendimientos con fragmentación

La mayoría de las masas rocosas que se desprenden se fragmentan en los primeros impactos contra el terreno. El riesgo asociado a los desprendimientos debe calcularse, por lo tanto, teniendo en cuenta este proceso de fragmentación. Para incorporar la fragmentación en la simulación de trayectorias es necesario prever el número y el volumen de los fragmentos rocosos resultantes en cada desprendimiento. Se presenta aquí un método para estimar estas dos variables. Se parte de la hipótesis que la distribución del volumen de los bloques acumulados en el canchal puede ser utilizada para generar aleatoriamente conjuntos de bloques, cada uno de ellos simulando el conjunto de bloques resultantes de un desprendimiento. Esta aproximación se ha aplicado a un canchal del Solà d’Andorra, Andorra la Vella (Principado de Andorra). La validez del método se ha contrastado comparado los resultados obtenidos con lo observado en desprendimientos recientes, inventariados por un plan de vigilancia de la zona.Postprint (published version

Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age

Terrestrial cosmogenic nuclide dating of ice-marginal moraines can provide unique insights into Quaternary glacial history. However, pre- and post-depositional exposure histories of moraine boulders can introduce geologic uncertainty to numerical landform ages. To avoid geologic outliers, boulders are typically selected based on their depositional context and individual characteristics but while these criteria have good qualitative reasoning, many have not been tested quantitatively. Of these, boulder location is critical, as boulders located on moraine crests are prioritised, while those on moraine slopes are typically rejected. This study provides the first quantitative assessment of the relative utility of moraine crest and moraine slope sampling using new and published 10Be and 36Cl ages (n = 19) and Schmidt hammer sampling (SH; n = 635 moraine boulders, ∼19,050 SH R-values) in the northern and southern Pyrenees. These data show that for many of the studied moraines, the spatial distribution of “good” boulders is effectively random, with no consistent clustering on moraine crests, ice-proximal or -distal slopes. In turn, and in contrast to prior work, there is no clear penalty to either moraine crest or moraine slope sampling. Instead, we argue that landform stability exerts a greater influence on exposure age distributions than the characteristics of individual boulders. For the studied landforms, post-depositional stability is strongly influenced by sedimentology, with prolonged degradation of matrix-rich unconsolidated moraines while boulder-rich, matrix-poor moraines stabilised rapidly after deposition. While this pattern is unlikely to hold true in all settings, these data indicate that differences between landforms can be more significant than differences at the intra-landform scale. As ad hoc assessment of landform stability is extremely challenging based on geomorphological evidence alone, preliminary SH sampling, as utilised here, is a useful method to assess the temporal distribution of boulder exposure ages and to prioritise individual boulders for subsequent analysis

Pérdida de suelo en laderas bajo cambio climático. procesos físicos, modelación predictiva y posibles estrategias de mitigación : el proyecto de investigación “Smucphy”

RESUMEN: Este proyecto de investigación estudia los mecanismos de la pérdida de suelos en zonas montañosas mediante un método multidisciplinar y el trabajo a diferentes escalas. Uno de los objetivos principales es analizar el efecto del cambio climático sobre estos mecanismos y buscar métodos de mitigación para afrontarlo correctamente. Se utilizan datos obtenidos mediante la auscultación de un experimento físico a gran escala y cuatro laderas y cuencas naturales situadas en el Pirineo Catalán, para alimentar y validar un modelo numérico innovador que implementa un módulo de interacciones suelo-vegetación-atmósfera. Finalmente, los resultados de la auscultación y de la modelización numérica se usarán para realizar una correlación de factores condicionantes de la inestabilidad con la ocurrencia espacio-temporal de deslizamientos superficiales utilizando técnicas SIG a escala regional. 1200Peer ReviewedPostprint (published version

Rockfall travel distance analysis by using empirical models (Solà d'Andorra la Vella, Central Pyrenees)

The prediction of rockfall travel distance below a rock cliff is an indispensable activity in rockfall susceptibility, hazard and risk assessment. Although the size of the detached rock mass may differ considerably at each specific rock cliff, small rockfall (<100 m3) is the most frequent process. Empirical models may provide us with suitable information for predicting the travel distance of small rockfalls over an extensive area at a medium scale (1:100 000¿1:25 000). "Solà d'Andorra la Vella" is a rocky slope located close to the town of Andorra la Vella, where the government has been documenting rockfalls since 1999. This documentation consists in mapping the release point and the individual fallen blocks immediately after the event. The documentation of historical rockfalls by morphological analysis, eye-witness accounts and historical images serve to increase available information. In total, data from twenty small rockfalls have been gathered which reveal an amount of a hundred individual fallen rock blocks. The data acquired has been used to check the reliability of the main empirical models widely adopted (reach and shadow angle models) and to analyse the influence of parameters which affecting the travel distance (rockfall size, height of fall along the rock cliff and volume of the individual fallen rock block). For predicting travel distances in maps with medium scales, a method has been proposed based on the "reach probability" concept. The accuracy of results has been tested from the line entailing the farthest fallen boulders which represents the maximum travel distance of past rockfalls. The paper concludes with a discussion of the application of both empirical models to other study areas

Rockfall travel distance analysis by using empirical models (Solà d'Andorra la Vella, Central Pyrenees)

The prediction of rockfall travel distance below a rock cliff is an indispensable activity in rockfall susceptibility, hazard and risk assessment. Although the size of the detached rock mass may differ considerably at each specific rock cliff, small rockfall (<100 m3) is the most frequent process. Empirical models may provide us with suitable information for predicting the travel distance of small rockfalls over an extensive area at a medium scale (1:100 000¿1:25 000). "Solà d'Andorra la Vella" is a rocky slope located close to the town of Andorra la Vella, where the government has been documenting rockfalls since 1999. This documentation consists in mapping the release point and the individual fallen blocks immediately after the event. The documentation of historical rockfalls by morphological analysis, eye-witness accounts and historical images serve to increase available information. In total, data from twenty small rockfalls have been gathered which reveal an amount of a hundred individual fallen rock blocks. The data acquired has been used to check the reliability of the main empirical models widely adopted (reach and shadow angle models) and to analyse the influence of parameters which affecting the travel distance (rockfall size, height of fall along the rock cliff and volume of the individual fallen rock block). For predicting travel distances in maps with medium scales, a method has been proposed based on the "reach probability" concept. The accuracy of results has been tested from the line entailing the farthest fallen boulders which represents the maximum travel distance of past rockfalls. The paper concludes with a discussion of the application of both empirical models to other study areas

Aproximación probabilística al número y tamaño de bloques en desprendimientos con fragmentación

La mayoría de las masas rocosas que se desprenden se fragmentan en los primeros impactos contra el terreno. El riesgo asociado a los desprendimientos debe calcularse, por lo tanto, teniendo en cuenta este proceso de fragmentación. Para incorporar la fragmentación en la simulación de trayectorias es necesario prever el número y el volumen de los fragmentos rocosos resultantes en cada desprendimiento. Se presenta aquí un método para estimar estas dos variables. Se parte de la hipótesis que la distribución del volumen de los bloques acumulados en el canchal puede ser utilizada para generar aleatoriamente conjuntos de bloques, cada uno de ellos simulando el conjunto de bloques resultantes de un desprendimiento. Esta aproximación se ha aplicado a un canchal del Solà d’Andorra, Andorra la Vella (Principado de Andorra). La validez del método se ha contrastado comparado los resultados obtenidos con lo observado en desprendimientos recientes, inventariados por un plan de vigilancia de la zona

Aproximación probabilística al número y tamaño de bloques en desprendimientos con fragmentación

La mayoría de las masas rocosas que se desprenden se fragmentan en los primeros impactos contra el terreno. El riesgo asociado a los desprendimientos debe calcularse, por lo tanto, teniendo en cuenta este proceso de fragmentación. Para incorporar la fragmentación en la simulación de trayectorias es necesario prever el número y el volumen de los fragmentos rocosos resultantes en cada desprendimiento. Se presenta aquí un método para estimar estas dos variables. Se parte de la hipótesis que la distribución del volumen de los bloques acumulados en el canchal puede ser utilizada para generar aleatoriamente conjuntos de bloques, cada uno de ellos simulando el conjunto de bloques resultantes de un desprendimiento. Esta aproximación se ha aplicado a un canchal del Solà d’Andorra, Andorra la Vella (Principado de Andorra). La validez del método se ha contrastado comparado los resultados obtenidos con lo observado en desprendimientos recientes, inventariados por un plan de vigilancia de la zona

Monitoring of fast moving landslides in the Pyrenees

The paper presents the experience of two instrumented sites in the Pyrenees where debris flows and rock falls occur frequently. The first one is the debris-flow monitoring system in the Rebaixader catchment, Central Pyrenees, Spain, installed since summer 2009. It consists of sensors registering meteorological and infiltration data as well as geophones, radar, ultrasonic sensors and a video camera focusing on the detection and dynamics of the flows. 24 torrential flows (debris flows and debris floods) and also 5 block falls have been detected. The second site is a recently installed rockfall monitoring system at the Forat Negre couloir, in Andorra la Vella, Principality of Andorra. It consists of 5 geophones and a video camera. For the same area high resolution point clouds obtained by remote techniques such as digital photogrammetry and Terrestrial Laser Scanner additionally permit the assessment of rockfall volumes and geometry, overcoming access restrictions