On the likelihood of future eruptions in the Chilean Southern Volcanic Zone: interpreting the past century’s eruption record based on statistical analyses

Yvonne Dzierma,Heidi Wehrmann

doi:10.5027/andgeov39n3-a02

Abstract

A sequence of 150 explosive eruptions recorded during the past century at the Chilean Southern Volcanic Zone (SVZ) is subjected to statistical time series analysis. The exponential, Weibull, and log-logistic distribution functions are fit to the eruption record, separately for literature-assigned volcanic explosivity indices (VEI) ≥2 and VEI ≥3. Since statistical tests confirm the adequacy of all the fits to describe the data, all models are used to estimate the likelihood of future eruptions. Only small differences are observed between the different distribution functions with regard to the eruption forecast, whereby the log-logistic distribution predicts the lowest probabilities. There is a 50% probability for VEI ≥2 eruptions to occur in the SVZ within less than a year, and 90% probability to occur within the next 2-3 years. For the larger VEI ≥3 eruptions, the 50% probability is reached in 3-4 years, while the 90% level is reached in 9-11 years.

Highlights

The Chilean Southern Volcanic Zone (SVZ) is the volcanologically most active part of the Chilean Andes, stretching from Tupungatito (33.40°S, 69.80°W) in the wider Santiago region (Región Metropolitana) southwards to Cerro Hudson (45.90°S, 72.97°W) in central Patagonia
A sequence of 150 explosive eruptions recorded during the past century at the Chilean Southern Volcanic Zone (SVZ) is subjected to statistical time series analysis
The exponential, Weibull, and log-logistic distribution functions are fit to the eruption record, separately for literature-assigned volcanic explosivity indices (VEI) ≥2 and VEI ≥3

Summary

Introduction

The Chilean Southern Volcanic Zone (SVZ) is the volcanologically most active part of the Chilean Andes, stretching from Tupungatito (33.40°S, 69.80°W) in the wider Santiago region (Región Metropolitana) southwards to Cerro Hudson (45.90°S, 72.97°W) in central Patagonia. In particular Santiago de Chile, while not in the immediate vicinity of the volcanic chain, are located inside drainage channels from the Andes and would, in the event of a volcanic eruption, be threatened by possible lahars and pyroclastic flows. The entire region is endangered by fallout tephra from explosive eruptions, which may cover large areas at long distances from the eruptive source, reaching Argentina to the east.

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