La avalancha de rocas de la Coma d'Espòs, Pirineo Central, Lleida: un evento prehistórico catastrófico

Abstract

Rock avalanches are extreme phenomena present in ridges with steep slopes and height. In the Iberian Peninsula various deposits have been described and interpreted as rock avalanches, especially given its magnitude and extent. However there are few documented cases where the features of the genuine deposits of rock avalanche such as the flow structures, inverse grading, secondary lobes and long travel distance, are described. In this communication the description of the avalanche deposits of Coma d’Espòs, Central Pyrenees is presented. The source area of the avalanche has also been affected by other failure mechanisms. In the portion of the hillside above 2400 m elevation, a deep seated gravitational slope deformation develops. It is manifested by the presence of a double ridge crest, the collapse of the hillside, and distinct scarps. An earthflow with an area of 0.2km2 and about 1 Mm3 volume partially covers the avalanche deposits. The avalanche of Coma d’Espòs is the rock avalanche of known so far, with the greatest mobility in the Catalan Pyrenees. It occupies an area of about 0.5 km2 and a length greater than 2200 m in its main lobes. The volume is estimated at a minimum of 4 Mm3, the angle range of about 14 °, indicating extraordinary mobility and suggests that the avalanche moved at high speed during its emplacement. It is an example of the catastrophic potential of this type of events in the Pyrenees.