USE OF TREE DAMAGE AND TREE-RING INFORMATION TO UNDERSTAND THE DYNAMICS AND IMPROVE THE CARTOGRAPHY OF CANAL DEL ROC ROIG AVALANCHE PATH (VALL DE NÚRIA)

The map collection “Mapa de Zones d’Allaus” (MZA) (Avalanche Paths Map) 1:25.000 of the Institut Cartografic de Catalunya (ICC) has been made using different information sources: population inquiry, historical research, terrain features and vegetation checking. Other sources of information allow a higher resolution in the cartography, such as the detailed study of the effects on vegetation and tree-ring analysis. In a forested snow avalanche path, a dendrochro nological analysis of the trees and other woody species can provide acurate data about frequency, maximum avalanche area, and also aproximate extension of single events. Canal del Roc Roig avalanche path is a lateral gully of Nuria river which affects the Nuria rack railway at Pla de Sallent site. In this path, a study based on the vegetation and on the morphology and damage of trees (Dept. de Geodinamica i Geofisica of the Universitat de Barcelona and ICC) 1 and an extensive dendrochronological study of 470 trees have detected several avalanche episodes, some already known, but others not documented, such as the one that occurred in 1930 (ICC and the Dept. d’Ecologia of the Universitat de Barcelona) 2 . The cartography of Canal del Roc Roig avalanche path limits was improved after analysing all the data extracted from the trees affected by avalanches, and valuable information to assess frequency and magnitude of the avalanches that occur has been obtained. 1 Projects RISKNAT SGR2001 00081 and SEID REN2000-0518 2 Project ALUDEX REN2002-02768