Dendrogeomorphic investigation of debris-flow activity in the Patagonian Andes

CASTELLER ALEJANDRO; STOFFEL MARKUS; ARBELLAY ESTELLE; SEBASTIAN CRESPO; VILLALBA RICARDO; BRIAN LUCKMAN

Rovaniemi

Conferencia; WorldDendro 2010; 2010

Asociation for tree ring research, Arctic Centre, University of Lapland, Tree Ring Society, IUFRO

Debris flows are pervasive disturbances in the Patagonian Andes that increasingly affect settlements expanding towards the upper Andean valleys. However, written documents of this rapid mass-movement process are scarce, fragmented and limited in time. In this study, we conduct a tree-ring reconstruction of temporal patterns of debris-flow activity. The study site is called ?Brazo Huemul? and is adjacent to Lago Nahuel Huapí, Neuquén, Argentina (40°56´01´´S, 71°24´43´´W). We sampled 43 trees, which showed in all cases external evidence of past debris-flow activity. The sampled species are Austrocedrus chilensis, a native conifer from northern Patagonia, and some individuals of Pseudotsuga menziesii, a conifer 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 scars, tangential rows of traumatic resin ducts, eccentricity variations, reaction wood and abrupt growth changes. Preliminary results indicate that 1895, 1949, 1975, 1993, 1999 and 2004 are years with abundant evidence of debris-flow activity. Although most events occurred during the dormant season of trees, damage during the vegetation period was also registered. Regional temperature and precipitation records were analyzed to determine the climatic conditions that prompted these events.