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Title: Gas flow dynamics in the conduit of Strombolian explosions inferred from seismo-acoustic observations at Aso volcano, Japan
Authors: Ishii, Kyoka
Yokoo, Akihiko
Kagiyama, Tsuneomi
Ohkura, Takahiro
Yoshikawa, Shin
Inoue, Hiroyuki
Author's alias: 石井, 杏佳
横尾, 亮彦
鍵山, 恒臣
大倉, 敬宏
吉川, 慎
井上, 寛之
Keywords: Strombolian explosion
Aso volcano
Slug ascent velocity
Seismo-acoustic signals
Issue Date: 2-Feb-2019
Publisher: Springer Berlin Heidelberg
Journal title: Earth, Planets and Space
Volume: 71
Thesis number: 13
Abstract: Strombolian explosions are one of the most studied eruptive styles and are characterized by intermittent explosions. The mechanism of a Strombolian explosion is modeled as a large gas pocket (slug) migrating through the magma conduit and then bursting at the air–magma interface. These ascending and bursting processes of the slug induce characteristic seismo-acoustic signals during each explosion: very-long-period (VLP) seismic signals, eruption earthquake signals, and infrasound signals. However, at Stromboli volcano, it has been reported that the ascent velocity estimated from the time differences between observed signals is nearly an order of magnitude higher than that expected from laboratory experiments simulating slug ascent. This discrepancy between observation-based and experiment-based velocities has not yet been fully explained and strongly suggests that the conventional model of Strombolian explosions should be partially revised. In this study, we attempted to validate the model of Strombolian explosions by estimating the gas phase velocity in the conduit in the case of Aso volcano. We recorded seismo-acoustic signals accompanying Strombolian events at Aso volcano, Japan, in late April 2015 via our monitoring network, and the ascent velocity of the gas phase was determined from the difference in arrival times between the VLP signals and the infrasound signals. Our estimated velocity exceeded 100 m/s, which is much faster than the experimental value of 7.5 m/s predicted for Aso volcano. To explain this rapid ascent velocity, we propose a revised model describing the migration of the gas phase via a more complicated mechanism, such as annular flow. In this model, we assumed that the gas phase ascends in the conduit at high velocity while making a pathway leading to the magma surface, most likely due to a temporary increase in the gas flux. Our model will help to deepen the understanding of the complicated dynamics in the magma conduit during a Strombolian explosion.
Rights: © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
URI: http://hdl.handle.net/2433/236390
DOI(Published Version): 10.1186/s40623-019-0992-z
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