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Geological Society of America, GSA Bulletin, 3-4(126), p. 481-498, 2014

DOI: 10.1130/b30798.1

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The 600 yr eruptive history of Villarrica Volcano (Chile) revealed by annually laminated lake sediments

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment, and provide unique records of the recurrence interval and magnitude of such events. This study uses a multi-lake and multi-proxy analytical approach to obtain reliable and high-resolution records of past natural catastrophes from c. 600 year old annually-laminated (varved) lake sediment sequences extracted from two lakes, Villarrica and Calafquén, in the volcanically and seismically active Chilean Lake District. Using a combination of µXRF scanning, microfacies analysis, grain-size analysis, color analysis and magnetic-susceptibility measurements, we detect and characterize four different types of event deposits (EDs) (lacustrine turbidites; tephra-fall layers; runoff cryptotephras; lahar deposits) and produce a revised eruption record for Villarrica Volcano, which is unprecedented in its continuity and temporal resolution. Glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote Carrán-Los Venados Volcanic Complex, Quetrupillán Volcano and the Huanquihue Group in the studied lake sediments. Time series analysis shows 112 eruptions with a Volcanic Explosivity Index (VEI) ≥ 2 from Villarrica Volcano in the last c. 600 years, of which at least 22 also produced lahars. This significantly expands our knowledge on the eruptive frequency of the volcano in this time window, compared to the previously known eruptive history from historical records. The last VEI ≥ 2 eruption of Villarrica Volcano occurred in 1991. We estimate the probability of the occurrence of future eruptions from Villarrica Volcano, and statistically demonstrate that the probability of a 22-year repose period (anno 2013) without VEI ≥ 2 eruptions is ≤ 1.7 %. This new perspective on the recurrence interval of eruptions and historical lahar activity will help improve volcanic hazard assessments for this rapidly expanding tourist region, and highlights how lake records can be used to significantly improve historical eruption records in areas that were previously uninhabited.