Reconstructing snow avalanches in the Southeastern Pyrenees

A regional study of snow avalanche processes was undertaken in the SE Pyrenees. Dendrogeomorphology was used to date and reconstruct large-scale snow avalanche events that occurred in the last four decades. Dendrochronological analyses yielded the dates of nine winters when avalanches occurred in the recent past in six studied avalanche paths. Some of these avalanches were already known, but others had not been documented. In one case, the existing avalanche path map was improved with the dendrogeomorphological information of a larger past event. As a result of the dendrogeomorphological analyses, evidence for three regional-scale major avalanche years was identified in the SE Pyrenees from 1971 to 2004: 1971¿1972, 1995¿1996 and 2002¿2003. The specific synoptic atmospheric situations and the most likely nivometeorological and snowpack conditions that released these major avalanches were determined using weather data for the seasons of major avalanche releases. In 1971¿1972 the snow avalanche episode was characterized by a deep trough crossing the Pyrenees. In 1995¿1996 a variety of meteorological situations produced several episodes of major avalanches. In 2002¿2003 the more significant of two episodes was attributed to a north advection pumping an arctic air mass over the Pyrenees. The 1995¿1996 avalanche season proved to be the most notable in the four past decades in the Pyrenees.

Zonas de aludes en la Vallferrera: Clasificación y riesgo geomorfológico

La Vallferrera es una cuenca que se encuentra en el Pirineo Occidental Catalán, limitando al E con Andorra. En ella se ha realizado un estudio de las características de las zonas de aludes, desde dos perspectivas (MASES, 1991): En primer lugar se efectúa una descripción y una clasificación de las diferentes morfologías de las zonas de aludes comparando su distribución con algunos parámetros intrínsecos de la cuenca (litología, relieve preexistente, etc.). Se ha observado que las diferentes morfologías de las zonas de aludes son producto de la adaptación de éstas al relieve glacial preexistente. En segundo lugar se entra en el análisis del riesgo geomorfológico que los aludes comportan en esta zona del Pirineo, identificando cuatro sectores donde el riesgo es alto debido a la interferencia de éstos con la estructura social.

Calibration and application of the MN2D dynamics model to the avalanches of Las Leñas (Argentina)

During the winters of 1999 and 2000 large avalanches occurred in the ski resort of Las Leñas (Los Andes, Mendoza, Argentina). On 8 September 1999 an avalanche of new, dry snow ran over a path with a 1000 m vertical drop. On 30 June and on 1 July 2000 five avalanches of similar vertical drop, which start with new snow, entrained very wet snow during their descent, and evolved into dense snow avalanches. To use the MN2D dynamics model correctly, calibration of model parameters is necessary. Also, no previous works with the use of dynamics models exist in South America. The events used to calibrate the model occurred during the winters of 1999 and 2000 and are a good sample of the kind of avalanches which can occur in this area of the Andes range. By considering the slope morphology and topography, the snow and meteorological conditions and the results of the model simulations, it was estimated that these avalanches were not extreme events with a return period greater than one hundred years. This implies that, in natural conditions, bigger, extreme avalanches could happen. In this work, the MN2D dynamics model is calibrated with two different avalanches of the same magnitude: dry and wet. The importance of the topographic data in the simulation is evaluated. It is concluded that MN2D dynamics model can be used to simulate dry extreme avalanches in Argentinean Andes but not to simulate extreme wet avalanches, which are much more sensitive to the topography.

On the complementariness of infrasound and seismic sensors for monitoring snow avalanches

The paper analyses and compares infrasonic and seismic data from snow avalanches monitored at the Vallée de la Sionne test site in Switzerland from 2009 to 2010. Using a combination of seismic and infrasound sensors, it is possible not only to detect a snow avalanche but also to distinguish between the different flow regimes and to analyse duration, average speed (for sections of the avalanche path) and avalanche size. Different sensitiveness of the seismic and infrasound sensors to the avalanche regimes is shown. Furthermore, the high amplitudes observed in the infrasound signal for one avalanche were modelled assuming that the suspension layer of the avalanche acts as a moving turbulent sound source. Our results show reproducibility for similar avalanches on the same avalanche path.

Disseny i implementació d'una aplicació per a dispositius mòbils per identificar elements geològics en el terreny

En aquests treball es presenta el procés de disseny i desenvolupament d'una aplicació per a dispositius mòbils que permet millorar la localització i identificació de les zones d'allaus. L'aplicació anomenada IdAllau, té les següents funcions principals: emmagatzematge, geolocalització, fotografia, representació cartografica, realitat augmentada i recerca per proximitat. La aplicació s'ha desenvolupat amb Android i llibreries i API's de codi lliure (Osmdroid i Appunta); amb els avantatges i inconvenients que comporta treballar-hi. El resultat final és una aplicació que permetrà als tècnics identificar les zones d'allaus en el camp utilitzant principalment la realitat augmentada i la geolocalització amb cartografia temàtica

Disseny i instal·lació de pantalles flexibles antiallaus per a la protecció de la C-28 a la Vall d'Aran

Els treballs del present projecte contemplen el disseny i la instal lació de 5.250 m de pantalles flexibles antiallaus tipus Umbrelli, per tal de protegir la carretera C-28 dels efectes de les allaus. En concret les estructures es situaran a l’alçada del Pk 39 de la C-28, a uns 2 km, aproximadament del nucli de Baqueira, terme municipal del Naut Aran a la comarca de la Vall d’Aran. Amb la instal lació d’aquestes pantalles es pretén assegurar 40 hectàrees aproximadament del possible desencadenament d’allaus al vessant conegut com les Pales de Ruda.

Dendrochronological study of the avalanche path Canal del Roc Roig: first results of the ALUDEX Project in the Pyrenees

Historical data about ancient avalanches are scarce in the Pyrenees. Dendrochronology can provide new data about past avalanches and their return period, but up to now little research has been carried out with this purpose. The Aludex project aims to obtain information about the frequency and extent of extreme avalanches, using a dendrochronological and a nivo-meteorological approach. In this paper, we present the results of a dendrochronological study of the Canal del Roc Roig avalanche path which was affected by two extreme avalanches in February 1996. This first dendrochronological study has permitted us to assess the tree-ring signals due to avalanche events in 53 out of 132 dated trees. The trees presented a variety of responses to the 1996 avalanche events. It is shown that the type of tree-ring signal depends on tree age. The methodology has proved successful in detecting the 1996 and 1972 documented avalanche events, and provided outstanding evidence of undocumented past events such as one in 1930.

Using vegetation to characterize the avalanche to Canal del Roc Roig, Vall de Núria (Eastern Pyrenees, Spain)

Avalanche hazard maps of high accuracy are difficult to produce. For land-use planning and management purposes, a good knowledge of extreme run-out zones and frequencies of avalanches is required. In the present work, vegetation recognition (especially focused on Pinus uncinata trees) and dendrochronological techniques are used to characterize avalanches that have occurred in historical times, helping to determine both the extent of large or extreme avalanches and their occurrence in time. Vegetation was studied at the Canal del Roc Roig (eastern Pyrenees, Spain) avalanche path. The avalanches descending this path affect the railway that reaches the Vall de Núria resort and the run-up to the opposite slope. During winter 1996, two important avalanches affecting this path were well documented. These are compared with the results of the vegetation study, consisting of an inventory of flora, the recording of vegetation damages along eight transverse profiles at different altitudes on the path and a dendrochronological sampling campaign. The data obtained contributed to a characterization of the predominant snow accumulation in the starting zone, the 1996 avalanches and the range of frequencies of large avalanches. Also, traces of avalanches that increase the path mapped in the avalanche paths map published by the Institut Cartogràfic de Catalunya in 2000 were identified, improving the initial existing information.

Using vegetation to characterize the avalanche to Canal del Roc Roig, Vall de Núria (Eastern Pyrenees, Spain)

Avalanche hazard maps of high accuracy are difficult to produce. For land-use planning and management purposes, a good knowledge of extreme run-out zones and frequencies of avalanches is required. In the present work, vegetation recognition (especially focused on Pinus uncinata trees) and dendrochronological techniques are used to characterize avalanches that have occurred in historical times, helping to determine both the extent of large or extreme avalanches and their occurrence in time. Vegetation was studied at the Canal del Roc Roig (eastern Pyrenees, Spain) avalanche path. The avalanches descending this path affect the railway that reaches the Vall de Núria resort and the run-up to the opposite slope. During winter 1996, two important avalanches affecting this path were well documented. These are compared with the results of the vegetation study, consisting of an inventory of flora, the recording of vegetation damages along eight transverse profiles at different altitudes on the path and a dendrochronological sampling campaign. The data obtained contributed to a characterization of the predominant snow accumulation in the starting zone, the 1996 avalanches and the range of frequencies of large avalanches. Also, traces of avalanches that increase the path mapped in the avalanche paths map published by the Institut Cartogràfic de Catalunya in 2000 were identified, improving the initial existing information.

Aludes de nieve. Riesgo actual y riesgo futuro.

Los aludes son fenómenos recurrentes que se producen con una gran variedad de situaciones nivo-meteorológicas. Las actuaciones para minimizar el riesgo son básicamente dos: la predicción temporal (boletín del peligro de aludes), que hay que mantener, y la predicción en el espacio (cartografías). El riesgo de ser afectado por un alud se percibe con total indefensión por la población cuando un alud de gran magnitud impacta sobre un edificio o una infraestructura. Por tanto, es necesaria una legislación del uso de suelo que obligue a considerar los riesgos naturales en la calificación de suelos no urbanizables, basada en mapas de inventario y peligrosidad. Así se puede proteger a la población no especialista frente a las amenazas naturales extremas. Respecto al cambio climático, el IPCC, en su Tercer Informe de Evaluación expone una serie de probables escenarios de cambio climático a escala global. En todos ellos se concluye que muy probablemente las temperaturas mínimas serán más altas (irán en aumento), habrá menos días fríos, días de heladas y olas de frío en casi todas las zonas continentales. esto va a conllevar la elevación de la isoterma de 0ºC hacia mayores altitudes y, por lo tanto, la elevación del límite del manto nivoso continuo durante el invierno hacia mayores altitudes. Respecto a la precipitación y también a escala global, no se puede concluir que vaya a haber un incremento positivo de los eventos de temporal extremos, por lo que no se puede concluir que vaya a haber una variación del número de aludes extremos. Respecto al riesgo futuro, en el mejor de los casos se van a seguir produciendo aludes de la misma o mayor magnitud y en los mismos lugares. El deterioro del bosque de protección es muy probable, por lo será necesaria una buena gestión forestal. La minimización del riesgo deberá basarse en una buena legislación y una buena gestión territorial.

Characterizing major avalanche episodes in space and time in the twentieth and early twentyfirst centuries in the Catalan Pyrenees

With the aim of better understanding avalanche risk in the Catalan Pyrenees, the present work focuses on the analysis of major (or destructive) avalanches. For such purpose major avalanche cartography was made by an exhaustive photointerpretation of several flights, winter and summer field surveys and inquiries to local population. Major avalanche events were used to quantify the magnitude of the episodes during which they occurred, and a Major Avalanche Activity Magnitude Index (MAAMI) was developed. This index is based on the number of major avalanches registered and its estimated frequency in a given time period, hence it quantifies the magnitude of a major avalanche episode or winter. Furthermore, it permits a comparison of the magnitude between major avalanche episodes in a given mountain range, or between mountain ranges, and for a long enough period, it should allow analysis of temporal trends. Major episodes from winter 1995/96 to 2013/14 were reconstructed. Their magnitude, frequency and extent were also assessed. During the last 19 winters, the episodes of January 22-23 and February 6-8 in 1996 were those with highest MAAMI values,followed by January 30-31, 2003, January 29, 2006, and January 24-25, 2014. To analyze the whole twentieth century, a simplified MAAMI was defined in order to attain the same purpose with a less complete dataset. With less accuracy, the same parameters were obtained at winter time resolution throughout the twentieth century. Again, 1995/96 winter had the highest MAAMI value followed by 1971/72, 1974/75 and 1937/38 winter seasons. The analysis of the spatial extent of the different episodes allowed refining the demarcation of nivological regions, and improving our knowledge about the atmospheric patterns that cause major episodes and their climatic interpretation. In some cases, the importance of considering a major avalanche episode as the result of a previous preparatory period, followed by a triggering one was revealed.