Meteorological triggers of debris flows in the patagonian Andes

CASTELLER A.; CRESPO S.; VILLALBA R.; ARANEO D. C.; STOFFEL M.

Mendoza

Congreso; CONGREMET XI; 2012

Centro Argentino de Meteorólogos

Debris flows are common natural hazards affecting infrastructure in the Patagonian Andes. Previous studies have shown that debris flows events have a strong correlation with local meteorological conditions, in particular precipitation. In this study, we investigate the meteorological conditions that triggered events between 1864 and 2009 at the site ‘Brazo Huemul’, Neuquén, Argentina (40°56'01''S, 71°24'43''W). In this region, written documents of this rapid mass-movement process are scarce, fragmented and limited in time. Dendrochronological methods were therefore used as a proxy record to reconstruct past events. We sampled 43 trees, which showed external evidence of past debris-flow activity. Sampled species were Austrocedrus chilensis (native) and Pseudotsuga menziesii (introduced from North America). We collected cross-sections and/or increment cores from the stems of both species, as well as exposed roots from selected trees. On each sample, we dated and analyzed tree-ring indicators of debris flows activity, such as scars, tangential rows of traumatic resin ducts, eccentricity variations, reaction wood and abrupt growth changes. Our results indicate that although most events occurred during the dormant season of trees (between April and September), damage also occurred during the growing season. Regional temperature and precipitation records were analyzed to determine the meteorological conditions that triggered these events. Preliminary results suggest that local precipitation, in many cases not registered at regional meteorological stations, are linked with the reconstructed events. We hypothesize that the presence of snow before rain events on the upper slopes of the catchment area would facilitate the occurrence of debris flows.