Probabilistic Volcanic Hazard Assessment for Pyroclastic Density Currents From Pumice Cone Eruptions at Aluto Volcano, Ethiopia

Pablo Tierz,Gezahegn Yirgu,Ben Clarke,Eliza Calder

doi:10.3389/feart.2020.00348

Abstract

Aluto volcano, in the Main Ethiopian Rift, is a peralkaline caldera system, which comprises conglomerations of rhyolite (obsidian) lavas and enigmatic pumice cones. Recent work has found that pumice cone eruptions are highly unsteady, and form convective eruption plumes that frequently collapse to generate pyroclastic density currents (PDCs). We develop a methodology and present results for the first probabilistic volcanic hazard assessment (PVHA) for PDCs at a pumice cone volcano. By doing so, we estimate the conditional probability of inundation by PDCs around Aluto volcano (Ethiopia), incorporating the aleatory uncertainty in PDC hazard. We employ a Monte Carlo energy cone modelling approach, which benefits from parameterisation informed by field investigations and volcanic plume modelling. We find that despite the relatively modest eruptions that are likely to occur, the wide distribution of past vent locations (and thus the high uncertainty of where future vents might open), results in a broad area being potentially at risk of inundation by PDCs. However, the aleatory uncertainty in vent opening means that the conditional probabilities are lower (= 0.05) regions of Aluto caldera. The Monte Carlo energy cone modelling approach provides a quantitative, accountable and defendable background and long-term PVHA for PDCs from Aluto. These results could be combined in the future with hazard assessments relating to tephra fall and/or lava to develop a comprehensive volcanic hazard map for the caldera.

Highlights

Pumice cone eruptions are some of the least studied forms of volcanic activity on Earth, yet represent the typical eruptive style at caldera volcanoes along the Main Ethiopian rift valley (Fontijn et al, 2018)
We identify 96 vents which are visible at the surface on and around the Aluto edifice and, there is a wide area from which hazardous volcanic processes, such as pyroclastic density currents (PDCs) or tephra fallout, could be sourced during future eruptions
By informing a Monte Carlo energy cone model with field constraints, volcanic plume modeling and global proxy data sets, we have developed the first probabilistic volcanic hazard assessment (PVHA) for a pumice cone volcano

Summary

Introduction

Pumice cone eruptions are some of the least studied forms of volcanic activity on Earth, yet represent the typical eruptive style at caldera volcanoes along the Main Ethiopian rift valley (Fontijn et al, 2018) They have been documented on Mayor Island, New Zealand (Houghton and Wilson, 1989), and are characteristic of the more recent volcanism on Pantelleria, Italy (Orsi et al, 1989). The increasingly high exposure to volcanic hazards in Ethiopia (Vye-Brown et al, 2016), and the recent recognition of the potential hazards at these volcanoes (Fontijn et al, 2018; Clarke et al, 2019; Clarke, 2020), evokes an urgent need for quantitative, accountable, and defendable volcanic hazard assessment (e.g., Connor et al, 2001; Newhall and Hoblitt, 2002; Marzocchi et al, 2010; Calder et al, 2015)

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Conclusion