A New Tree-Ring-Based, Semi-Quantitative Approach for the Determination of Snow Avalanche Events: use of Classification Trees for Validation
Résumé
On forested paths, dendrogeomorphology has been demonstrated to represent a powerful Vincent Jomelli* tool to reconstruct past activity of avalanches, an indispensable step in avalanche hazard Delphine Grancher* assessment. Several quantitative and qualitative approaches have been shown to yield Markus Stoffel † ‡ reasonable event chronologies but the question of the completeness of tree-ring records remains debatable. Here, we present an alternative semi-quantitative approach for the Christophe Corona † determination of past snow avalanche events. The approach relies on the assessment of Daniel Brunstein* the number and position of disturbed trees within avalanche paths as well as on the Nicolas Eckert § and intensity of reactions in trees. In order to demonstrate that no bias was induced by the dendrogeomorphic expert, we carry out a statistical evaluation (Classification and Regres-Michael Deschatres § sion Trees, or CART) of the approach. Results point to the consistency and replicability *Laboratoire de Géographie Physique, of the procedure and to the fact that the approach is not restricted to the identification of Université Panthéon-Sorbonne, UMR high-magnitude avalanches. Evaluation of the semi-quantitative approach is illustrated on 8591 CNRS, 1 place Aristide Briand, Fa well-documented path in Chamonix, French Alps. For the period 1905-2010, comparison 92195 Meudon cedex, France †Dendrolab.ch, Institute of Geological between the avalanche years recorded in a substantial database (Enquête Permanente sur Sciences, University of Berne, les Avalanches, or EPA) and those defined with dendrogeomorphic techniques shows that Baltzerstrasse 1 ם 3, CH-3012 Berne, the avalanche record reconstructed from tree-ring series contains 38% of the observed Switzerland events.
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