Mechanism of small vulcanian eruptions at Suwanose

Authors: Takeshi Nishimura Masato Iguchi Hiroshi Yakiwara Jun Oikawa Ryohei Kawaguchi Hiroshi Aoyama Haruhisa Nakamichi Yusaku Ohta Takeshi Tameguri

Publish Date: 2013/11/20

Volume: 75, Issue: 12, Pages: 779-

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Abstract

We examine precursory signals of vulcanian eruptions at Suwanosejima volcano southwest of Japan by deploying seismic and tilt stations close to the active crater to understand the shallow conduit processes just before explosions Vulcanian eruptions at Suwanosejima for the period from October 2009 to 2011 are often preceded by a sudden cessation of continuous tremor associated with continuous ash emissions The amplitude of continuous tremor decreases within about 10 s and tilt signal starts to show uplift of the active crater Then the pause of continuous tremor and uplift continue for about 1–2 min and tilt amplitudes reach a few tens of nanoradians at a distance of 400 m from the active crater As the pause time of continuous tremor before explosion becomes longer the maximum amplitude of explosion earthquake and uplift signal become larger Vulcanian eruptions are also observed during periods without continuous tremor In these cases tilt signals capture uplifts of the active crater for about 10 min before explosions and reach a few tens of nanoradians Cessations of volcanic gas emissions are observed before some explosions during periods without continuous tremor Mori et al 2011 These observations suggest that pressurization in the shallow conduit is caused by an accumulation of volcanic gases and ash through the formation of ‘cap’ in the conduit possibly composed of stiffened magma due to degassing cooling rheological changes or other mechanismsWe appreciate Toshima village office for the approval of our observation at Suwanosejima volcano Realtime monitoring by staffs of Sakurajima Volcano Research Center Kyoto University helped us to have safe observations at the active volcano We thank the staffs of Kyushu Electric Engineering Consults that dug boreholes for our tilt measurement on the steep flanks of the Suwanosejima volcano Constructive and suggestive comments by associate editor Michael Manga Greg Waite and John Lyons were very helpful to improve the manuscript Taketo Shimano provided us useful information on the property of volcanic ejecta at Suwanosejima This study is supported by the Ministry of Education Culture Sports Science and Technology MEXT of Japan under its Observation and Research Program for Prediction of Earthquakes and Volcanic Eruptions

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