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

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.

Permeability Evolution in Variably Glassy Basaltic Andesites Measured Under Magmatic Conditions

“…We note that the Type 3 rock contains only trace glass phase and the DSC peak is small but present. This glass transition temperature is consistent with an H 2 O content of 1.1 wt % (we derived the viscosities using Giordano et al, and the average glass composition given by Erdmann et al, and Preece et al, ). In all samples, the glass transition peak is followed by a large endothermic peak beginning at 690°C that is associated with a large mass loss event (shown by thermogravimetric analysis, see Figure S6).…”

Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador

“…The magma experienced only a relatively small amount of syn-explosive expansion (3 to 34 %) because it already experienced significant closed-system degassing during ascent and residence in the conduit. Feldspar number densities are substantially reduced in this zone (300 to 7000 mm -2 , Figure 11) when compared with the plug-rock which is consistent with lower undercooling, and therefore with the dominance of crystal growth over nucleation (Hammer et al, 2000;Hammer and Rutherford, 2002;Preece et al, 2016;Shea and Hammer, 2013). This is confirmed by A cluster of the collected samples were evacuated from approx.…”

“…Pl, CPx, OPx, and Amp. are plagioclase, clinopyroxene, orthopyroxene, and amphibole, respectively (Hammer et al, 1999), Mt Pelee 1902, various eruptions of Merapi 1986(Preece et al, 2016Hammer et al, 2000), Galeras 2004(Bain et al, 2018 and Soufrière Hills Volcano 1997 (Clarke et al, 2007). (b) Experimental decompression data from continuous decompression experiments (Riker et al, 2015;Brugger and Hammer, 2010b;Martel, 2012), single step decompression experiments (Riker et al, 2015;Couch et al, 2003;Brugger and Hammer, 2010b) and multistep decompression experiments (Brugger and Hammer, 2010b Shea and Hammer (2013) and Andujar et al (2017) and from the bulk composition analysis of ash from the 14 July 2013 explosion.…”

“…Relatively high number densities usually occurs as a result of moderate undercooling in the rising magma (Hammer et al, 1999;Hammer and Rutherford, 2002) although, the absence of disequilibrium crystal morphologies in these samples suggests only low to moderate decompression rates (Couch et al, 2003). In this case, the long residence times of the magma (>6 weeks since the last eruptive event) indicates that crystal and vesicle textures in the plug samples are more likely the result of the dwell time at low pressure rather than ascent (Preece et al, 2016). Efficient outgassing under open-system conditions is also suggested by the textural characteristics exhibited by the plug rock samples particularly, their low porosity nature,…”

Quiescent‐explosive transitions during dome‐forming volcanic eruptions: Using seismicity to probe the volcanic processes leading to the 29 July 2008 vulcanian explosion of Soufrière Hills Volcano, Montserrat

“…These violent episodes of explosive activity are often associated with long-lived dome-forming eruptions. Recent examples include Colima, Mexico; Santiaguito, Guatemala; Merapi, Indonesia; and Soufrière Hills Volcano, Montserrat [Cassidy et al, 2015;Bluth and Rose, 2004;Surono et al, 2012;Cole et al, 2014a] and are often ascribed to the buildup of gas pressure within a cooling and crystallizing viscous magma in a shallow conduit [e.g., Self et al, 1979;Stix et al, 1997;Diller et al, 2006], perhaps linked to changes in the flux of hotter magma at depth [e.g., Preece et al, 2016].…”