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Title: Pre-eruptive excess volatiles and their relationship to effusive and explosive eruption styles in semi-plugged volcanoes
Authors: Utami, Sri Budhi
Andùjar, Juan
Costa, Fidel
Scaillet, Bruno
Humaida, Hanik
Carn, Simon
Keywords: Science::Geology
Issue Date: 2022
Source: Utami, S. B., Andùjar, J., Costa, F., Scaillet, B., Humaida, H. & Carn, S. (2022). Pre-eruptive excess volatiles and their relationship to effusive and explosive eruption styles in semi-plugged volcanoes. Frontiers in Earth Science, 10, 882097-.
Project: NRFNRFI2017-06 
Journal: Frontiers in Earth Science 
Abstract: Understanding the role of various factors influencing eruption style is challenging, but it can aid in adapting different hazard mitigations and crisis responses for explosive or effusive events. Here, we focus on the role of magma storage conditions in controlling eruption styles at basaltic andesite volcanoes, and how they can be related to monitoring data. We study the cycle of explosive (1990, sub-Plinian) → effusive (2007, dome) → explosive (2014, sub-Plinian) eruptions from Kelud (Kelut) volcano, Indonesia. We conducted petrological analyses of the eruption products and phase equilibria experiments using pumice and explored a range of temperatures, pressures, oxygen fugacity, and volatile contents. We show that we can reproduce the main mineral assemblage (plagioclase ± pyroxenes ± magnetite ± amphibole ± olivine) and phenocryst content (30–50 wt%) of the magmas from the three eruptions at T = 975 ± 39°C, p = 175 ± 25 MPa, fO2 = nickel–nickel oxide buffer, and about 4–6 wt% water in the melt (ca. 3 to 5 wt% and ca. 4 to 7 wt% for the 1990 and 2014 eruptions, respectively). However, geothermobarometric results also indicate that some crystals of amphibole were sourced from higher pressures. We infer from a synthesis of our data and historical observations that the high phenocryst content of the 2007 dome (∼70 wt%) likely resulted from slow magma ascent toward the surface alongside progressive degassing and re-equilibration at a lower volatile content (∼1 wt% water in the melt). Mass balance calculations on the sulfur budget of the 1990, 2007, and 2014 magmas show that the explosive events contained an excess fluid phase at pre-eruptive conditions, and we propose that this led to their higher explosivity compared to the 2007 dome. The accumulation of excess fluids during decadal-long repose depends on how plugged the volcanic system is, or its ability to passively release magmatic fluids, prior to eruption. Such condition could be inferred from monitoring records, including changes in gravity of the plumbing system over time, and thus contribute to better anticipate eruptive style.
ISSN: 2296-6463
DOI: 10.3389/feart.2022.882097
Schools: Asian School of the Environment 
Research Centres: Earth Observatory of Singapore 
Rights: © 2022 Utami, Andùjar, Costa, Scaillet, Humaida and Carn. This is an openaccess article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Fulltext Permission: open
Fulltext Availability: With Fulltext
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EOS Journal Articles

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