Pôle Alpin Risques Naturels (PARN) Alpes–Climat–Risques Avec le soutien de la Région Rhône-Alpes (2007-2014)
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Réf. Corona & al 2013 - A

Référence bibliographique
CORONA, C., LOPEZ SAEZ, J., STOFFEL, M., ROVÉRA, G., EDOUARD, J.-L., BERGER, F. 2013. Seven centuries of avalanche activity at Echalp (Queyras massif, southern French Alps) as inferred from tree rings. The Holocene, Vol. 23(2), 292–304. PDF

Abstract: The purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the Queyras massif (Echalp avalanche path, southeast French Alps). Analysis of past events was based on tree-ring series from 163 heavily affected multicentennial larch trees (Larix decidua Mill.) growing near or next to the avalanche path. A total of 514 growth disturbances, such as tangential rows of traumatic resin ducts, the onset of compression wood as well as abrupt growth suppression or release, were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010. The mean return period of snow avalanches was 22 years with a 4% probability that an avalanche occurs in a particular year. On a temporal plan, three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850, correlating with below-average winter temperatures and glacier advances. Analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events. The comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events – six of which were undocumented – reached the hamlet of Echalp during the last seven centuries, but no significant temporal trend was detected concerning the frequency of these extreme events.

Mots-clés

Dendrogeomorphology - French Alps - Frequency - Multicentennial reconstruction - Snow avalanche - Tree-rings


Organismes / Contact

• Laboratory of Dendrogeomorphology (dendrolab.ch), Institute of Geological Sciences, University of Berne, Switzerland
• IRSTEA, UR EMGR, France
• Chair for Climatic Change and Climate Impacts, Institute for Environmental Sciences, University of Geneva, Switzerland
• Université Grenoble-I Joseph Fourier, UMR 5194-CNRS PACTE Territoires, France
• Centre Camille Julian UMR 6573 CNRS, Maison Méditerranéenne des Sciences de l’Homme, France


(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
       

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
           

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 
 

(4) - Remarques générales
 

(5) - Syntèses et préconisations
Conclusion

In mountain areas such as the Alps, the increase in human activity has resulted in increased risks for natural hazards such as snow avalanches. Therefore, it has become imperative to improve avalanche forecasting at the local level. Nevertheless, because anticipated changes in climate may alter the dynamics of slope processes and the frequency or magnitude of extreme events, understanding the mechanisms that link climate and avalanche activity is the first step in any attempt at forecasting. In that respect, analyses based on long historical records of avalanche occurrences can be very useful for improving avalanche prediction.

This study demonstrates that, in multicentennial stands, dendrogeomorphic methods clearly have the potential to reconstruct past avalanche events for several centuries and to add substantially to the historic record. Furthermore, the maxima detected in snow avalanche frequency are correlated with glacier advances and below average temperature, thus confirming the existence of a climatic signal in avalanche frequency fluctuations.

In addition, dendrogeomorphic data can add evidence to the extent of past events where other sources often fail to produce conclusive results. The method enables an accurate mapping of events. The comparison with the CLPA clearly demonstrates that it adds evidence on the runout distance of large events and that the lateral spread of past avalanches can be better defined. Nonetheless, assessing the result of this study, particularly concerning the effect of recent climate change, could be accomplished by (1) replicating studies for a larger number of avalanche paths in order to improve the significance of the observed trends and (2) using weather station instrumentation at remote sites, calibrated against long meteorological time series, to obtain more relevant data for modeling.

Références citées :

 


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