Lago Puyehue sedimentary record of Valdivia 1960 major earthquake and associated volcanic eruption in the Chilean Lake District
by
Emmanuel Chapron
ETH Zurich
Coauthors: M. Pino (Instituto de Geosciencias, Univ Austral de Valdivia, Chile); F. Charlet (RCMG, Ghent University, Belgium), S. Bertrand (UR Argiles et Climat, Liege University, Belgium), O. Magand (LGGE, CNRS-Observatory of Grenoble, France), F. Arnaud (EDYTEM, University of Savoie, France), M Debatist (RCMG, Ghent University, Belgium) and R. Urrutia (Centro EULA,Universidad de Concepcion, Chile)

The synthesis of first results from a multidisciplinary study of Lago Puyehue (41°S) sedimentary infill involving high-resolution seismic profiling and multi-proxy analyses of sediment cores is presented. Sub-bottom profiling was essential to optimise the selection of two coring sites accumulating the clastic supply of the main tributary of the lake (the Golgol River). Age-depth models for coring sites PU II and PU I are based on radionuclide measurements (210Pb, 137Cs, 241 Am) on short cores and a detailed analysis of the core lithologies. These age-depth models are strongly supported by the reconnaissance of historic events such as the sedimentary record of 1960 Valdivia major earthquake and the eruptions of Puyehue volcano in 1960 and 1921-22. During this major subduction earthquake (M 9.5) many landslides where triggered in the catchment area of the Golgol River and some of them deeply affected the course of the river. In the lake basin, only limited slope instabilities can be attributed to this event on seismic profiles and at PU II coring site. The volcanic eruption of Puyehue-Cordon-Call volcanic complex two days after the earthquake produced large volumes of pumiceous ash, but strong SW winds favoured ash deposition only on the upper catchment of the Golgol. At the end of the 1960 winter, heavy rain falls and snow melt resulted in the development of a major flood event that formed a 40 cm thick hyperpycnal flood deposit in front of the delta at PU I coring site. PU I and PU II coring sites are characterised by contrasted sedimentary processes and sensitivities to the active geodynamic setting of the SW Andes. Detailed continuous paleo-environmental reconstructions in the study area should be based on coring site PU II.

Date received: October 23, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caod-08.