Transitions between explosive and effusive phases during the cataclysmic 2010 eruption of Merapi volcano, Java, Indonesia.

Katie Preece,Jean-Christophe Komorowski,Ralf Gertisser,Richard A Herd,Jenni Barclay,Sylvain J Charbonnier

doi:10.1007/s00445-016-1046-z

Abstract

Transitions between explosive and effusive activity are commonly observed during dome-forming eruptions and may be linked to factors such as magma influx, ascent rate and degassing. However, the interplay between these factors is complex and the resulting eruptive behaviour often unpredictable. This paper focuses on the driving forces behind the explosive and effusive activity during the well-documented 2010 eruption of Merapi, the volcano’s largest eruption since 1872. Time-controlled samples were collected from the 2010 deposits, linked to eruption stage and style of activity. These include scoria and pumice from the initial explosions, dense and scoriaceous dome samples formed via effusive activity, as well as scoria and pumice samples deposited during subplinian column collapse. Quantitative textural analysis of groundmass feldspar microlites, including measurements of areal number density, mean microlite size, crystal aspect ratio, groundmass crystallinity and crystal size distribution analysis, reveal that shallow pre- and syn-eruptive magmatic processes acted to govern the changing behaviour during the eruption. High-An (up to ∼80 mol% An) microlites from early erupted samples reveal that the eruption was likely preceded by an influx of hotter or more mafic magma. Transitions between explosive and effusive activity in 2010 were driven primarily by the dynamics of magma ascent in the conduit, with degassing and crystallisation acting via feedback mechanisms, resulting in cycles of effusive and explosive activity. Explosivity during the 2010 eruption was enhanced by the presence of a ‘plug’ of cooled magma within the shallow magma plumbing system, which acted to hinder degassing, leading to overpressure prior to initial explosive activity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00445-016-1046-z) contains supplementary material, which is available to authorized users.

Highlights

Transitions between explosive and effusive activity are commonly observed at many subduction zone volcanoes
This paper investigates what caused transitions between explosive and effusive activity during the VEI 4 eruption of Merapi volcano (Indonesia) in 2010, via textural and compositional analysis of feldspar groundmass microlites
The beginning and end of the 2010 eruption were controlled by magma flux from depth, but eruptive style and transitions between explosive and effusive activity were regulated by shallow conduit processes

Summary

Introduction

Transitions between explosive and effusive activity are commonly observed at many subduction zone volcanoes. It has been estimated that 95 % of dome eruptions are associated with an explosive component (Newhall and Melson 1983; Ogburn et al 2015). Dome-forming eruptions have transitioned between effusive behaviour and explosive Vulcanian and/or (sub)Plinian activity at Mount St. Helens, Montserrat, Pinatubo and Guagua Pichincha to name just a few Hammer et al 1999; Cashman and McConnell 2005; Clarke et al 2007; Wright et al 2007; Komorowski et al 2010). Understanding the driving forces behind eruptive style and factors that influence changes in activity is crucial for hazard assessment and monitoring efforts. A complex interplay of factors acts in each system to determine eruptive style, with previous results often

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