Dendrochronological reconstruction of spatial and temporal patterns of snow avalanches in the Patagonian Andes

CASTELLER, A., VILLALBA, R., STOECKLI, V.

Davos, Suiza

Conferencia; ISSW International Snow Science Workshop; 2009

WSL Institute for Snow and Avalanche Research SLF

Snow avalanches are a major natural hazard in a large number of mountainous regions around the world. Numerous roads and settlements in the Andes are located adjacent to avalanche tracks, for which little is known about maximum extents or return periods. Utilizing dendrochronological techniques, we were able to reconstruct occurrence dates and affected areas of past snow avalanche events. Individual Nothofagus pumilio trees with visible damage of past avalanche disturbances were sampled in the track, borders and run-out zones of 11 avalanche tracks located at “Loma de las Pizarras”, Santa Cruz, Argentina. Our analyses indicate that scars, eccentricity variations in the wood, abrupt growth changes and reaction wood are the main tree-ring indicators associated with avalanche disturbances in N. pumilio. Based upon a quantitative weighting of the different indicators and on the sampling height, we calculated an index of avalanche occurrences, which allowed us to determine for each avalanche track the years with avalanche occurrences. Considering the avalanche activity at a slope scale in the 11 studied tracks, the years with the largest number of events are 1936, 1966, 1978 and 1995. In addition, climatic records were analyzed in order to explore relationships between years with avalanche activity and regional monthly variations of temperature and precipitation. We found that the years with high frequency of avalanche events are significantly correlated with abundant precipitation. The results of this investigation confirm the dendrochronological potential of N. pumilio for reconstructing spatial and temporal patterns of snow avalanche events in the Patagonian Andes.