Explosive Eruptions With Little Warning: Experimental Petrology and Volcano Monitoring Observations From the 2014 Eruption of Kelud, Indonesia

J M Castro,S F L Watt,K Spaans,A Odell,P Kristianto,C Helo,H Triastuty,M Cassidy,C Caudron,H Gunawan,S K Ebmeier

doi:10.1029/2018gc008161

Abstract

AbstractExplosive eruptions that occur with little or no precursory unrest (less than a month) pose the greatest hazards from volcanoes to nearby populations. Here we focus on the preeruptive conditions for these explosive events, their triggers and how these eruptions evolve. We concentrate on Kelud volcano, where we have conducted a set of petrological experiments to understand preeruptive storage conditions for several recent eruptions. For the 2014 explosive eruption, we combine this with an analysis of interferometric synthetic aperture radar measured deformation. Our data suggest that both explosive and effusive eruptions at Kelud are sourced from a magma storage system at 2–4 km. However, explosive eruptions are fed by magma stored under relatively cool (~1000 °C) and water‐saturated conditions, whereas effusive eruptions are fed by slightly hotter (~1050 °C), water‐undersaturated magmas. We propose that the initial phase of the 2014 eruption was triggered by volatile overpressure, which then fostered top‐down decompression tapping discrete magma bodies. By compiling a global data set of monitoring signatures of explosive eruptions, we show that the onset of unrest rarely points to the shallow ascent of magma to the surface, as ascent mostly occurs in a matter of hours or minutes. We relate the timescale of preeruptive unrest to eruption triggering mechanisms, with yearly/decadal periods of unrest relating to magma injection events (which may or may not precede a magmatic eruption), whereas internal triggering (e.g., second boiling) of an already present, cooling magma body can lead to explosive eruptions with little warning.

Highlights

Recent studies suggest that arc magmas can remain in the upper crust for decades to millennia (Rubin et al, 2017), in a mostly crystalline/mushy state (Cooper & Kent, 2014) or even stored as multiple melt‐rich lenses from the middle to shallow crust (Edmonds et al, 2016) and that eruption can be triggered rapidly (e.g., Martin et al, 2008)
We relate the timescale of preeruptive unrest to eruption triggering mechanisms, with yearly/decadal periods of unrest relating to magma injection events, whereas internal triggering of an already present, cooling magma body can lead to explosive eruptions with little warning
This shows that most eruptions are sourced from reservoirs from 4 to 9 km, with no discernible difference between effusive and explosive eruptions, suggesting that storage pressure have little control on eruptive style, as we have found for the Kelud system

Summary

Introduction

Recent studies suggest that arc magmas can remain in the upper crust for decades to millennia (Rubin et al, 2017), in a mostly crystalline/mushy state (Cooper & Kent, 2014) or even stored as multiple melt‐rich lenses from the middle to shallow crust (Edmonds et al, 2016) and that eruption can be triggered rapidly (e.g., Martin et al, 2008). Whether a volcano erupts effusively or explosively is thought to be a product of how efficiently the magma can outgas, which is related to its viscosity and the rate at which it decompresses and ascends (Cassidy et al, 2018; Eichelberger et al, 1986; Gonnermann & Manga, 2007; Jaupart & Allègre, 1991). These parameters all differ depending on the conditions and processes that occur while in storage. Monitoring how the magmatic properties evolve throughout an eruption has the potential to help us forecast eruptive style transitions and when the eruption will end

Methods

Results

Discussion

Conclusion