Effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics: Gunung Merapi 2010 eruption
Kimberly Genareau, Shane J. Cronin, Gert Lube, 2015. "Effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics: Gunung Merapi 2010 eruption", The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas, G. F. Zellmer, M. Edmonds, S. M. Straub
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In 2010, Gunung Merapi (Central Java, Indonesia) generated two violent eruption sequences on 26 October and 5 November culminating in widespread pyroclastic density currents (PDCs) associated with the destruction of lava domes. Tephra from PDC deposits were analysed to examine pre-dome collapse volatile behaviour and evidence of carbonate assimilation. Secondary-ion mass spectroscopy (SIMS) depth profiles of plagioclase phenocrysts reveal that the 7Li/30Si ratios in 26 October products are higher in the glass compared to the crystal, indicating a build-up of Li in the groundmass not observed in the 5 November samples. Higher Li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 October explosion, which was only captured through the behaviour of quickly diffusing Li and not H2O. Following the explosion-induced decompression, juvenile magma rapidly ascended in great volume to generate extremely destructive PDCs following subsequent dome collapses, particularly on 5 November. Additionally, 26 October tephras contain carbonate grains in the ash component and abundant CO2 within the lava lapilli groundmass glass, which supports previous studies indicating assimilation of calc-silicate lithologies by the Merapi magma at depth in the plumbing system prior to the onset of 2010 activity.
Feldspar microlite compositions and SIMS volatile data for the glass measurements are available at http://www.geolsoc.org.uk/SUP18762.
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The subduction zone volatile cycle is key to understanding the petrogenesis, transport, storage and eruption of arc magmas. Volatiles control the flux of slab components into the mantle wedge, are responsible for melt generation through lowering the solidi of mantle materials and influence the crystallizing phase assemblages in the overriding crust. Further, the rates and extents of degassing during magma storage and decompression affect magma rheology, ultimately control eruption style and have consequences for the environmental impact of explosive arc volcanism. This book highlights recent progress in constraining the role of volatiles in magmatic processes.
Individual book sections are devoted to tracing volatiles from the subducting slab to the overriding crust, their role in subvolcanic processes and eruption triggering, as well as magmatic-hydrothermal systems and volcanic degassing. For the first time, all aspects of the overarching theme of volatile cycling are covered in detail within a single volume.