Applicability of statistical eruption analysis to the geological record of Villarrica and Lanín volcanoes, Southern Volcanic Zone, Chile

Abstract

Standard stochastic failure-analysis techniques are applied to the geological eruption records of Villarrica and Lanín volcanoes in the Chilean Southern Volcanic Zone. These statistical methods are used to estimate the probabilities of eruptions large enough to leave a trace in the geological record. For Villarrica, the standard lifetime distributions predict a near 100% probability that such an eruption should have occurred between 489 AD and today. If the VEI = 3 eruptions observed in the historical record are large enough to be preserved in the geological record, the probability of such a future eruption of Villarrica is about 20% in the next 100 years. In the case of Lanín, the applicability of the exponential, Weibull and log-logistic distributions to the geological record is doubtful, since the volcano appears to have experienced alternating high- and low-activity regimes. Only the mixture-of-exponentials distribution can take into account the possible dormancy descending to final extinction, resulting in a probability of about 16% that Lanín will ever erupt again in the future. The contrasting behaviour of the eruption records of these two neighbouring volcanoes in terms of the number of eruptions and the length of the repose-time intervals serves to examine to what extent the method can be applied to geological eruption records. This study contributes to directing statistical eruption analysis towards time scales long enough to investigate large-magnitude eruptions, and it includes the possibility of dormancy/extinction.