Reconstructing temporal patterns of snow avalanches at Lago del Desierto, southern Patagonian Andes

CASTELLER, A.; VILLALBA, R.; ARANEO, D.; STOECKLI, V.

COLD REGIONS SCIENCE AND TECHNOLOGY

ELSEVIER SCIENCE BV

Año: 2011 vol. 67 p. 68 - 78

0165-232X

Snow avalanches recurrently cause substantial damage to infrastructure and losses in human lives inmountainous environments around the world. Densely populated regions have suffered more intensely the destructive forces of avalanches; however, settlers of these regions have developed tools to mitigate avalanche risk, including avalanche hazard maps. To design detailed hazard maps, accurate information on avalanche runout and frequency is necessary. In areas where avalanches are mostly undocumented, like in the Andes, dendrochronological methods become a valuable tool for reconstructing spatio-temporal avalanche patterns. At Lago del Desierto (southern Patagonian Andes, Argentina), trees from nine avalanche tracks were sampled. Nothofagus pumilio, a winter deciduous broad-leaved tree, was sampled in all cases. Avalanche activity is recognized based on the presence of scars, changes in stem eccentricity, reaction wood and abrupt growth changes. A rating system was used to define the relative importance of each tree-ring indicator in thereconstructed chronology of events. According to this chronology, widespread avalanche activity on the slope was found for the years 1918, 1930, 1931, 1971, 1995 and 1998. Superposed Epoch Analysis indicated that total monthly precipitation during the three snowiest months from May to October of 1971, 1995 and 1998 (years for which climatic data exists for validation) was significantly greater than for years without large avalanche activity. In contrast, no significant correlations were found between monthly temperature variations and years with large avalanche activity on the slope. Atmospheric circulation patterns associated with years of major avalanche activity show features typically observed during the cold phase of the El Niño– Southern Oscillation cycle, i.e. La Niña. For those cases, results also show an increase in the westerlies across the South Pacific and southern South America, resulting in both higher precipitation and stronger winds over the study area that favor snow avalanche episodes. We point out the need of a more systematic sampling strategy in order to reconstruct spatial avalanche patterns in the southern Andes, which are a complement of temporal patterns to design hazard maps.