| Co-Investigator(Kenkyū-buntansha) |
清水 洋 九州大学, 理学研究院, 教授 (50178985)
宮町 宏樹 鹿児島大学, 理工学研究科, 教授 (30182041)
中道 治久 名古屋大学, 環境学研究科, 助教 (00420373)
大久保 修平 東京大学, 地震研究所, 教授 (30152078)
森田 裕一 東京大学, 地震研究所, 教授 (30220073)
石原 和弘 京都大学, 防災研究所, 教授 (30027297)
中尾 茂 鹿児島大学, 理工学研究科, 准教授 (90237214)
大倉 敬宏 京都大学, 理学研究科, 准教授 (40233077)
植木 貞人 東北大学, 理学研究科, 准教授 (40004501)
大島 弘光 北海道大学, 理学研究院, 准教授 (10213703)
上嶋 誠 東京大学, 地震研究所, 准教授 (70242154)
鍵山 恒臣 京都大学, 理学研究科, 教授 (50126025)
神田 径 東京工業大学, 火山流体研究センター, 准教授 (00301755)
橋本 武志 北海道大学, 理学研究院, 准教授 (70283588)
野上 健治 東京工業大学, 火山流体研究センター, 教授 (70251676)
森 俊哉 東京大学, 理学系研究科, 准教授 (40272463)
小林 哲夫 鹿児島大学, 理工学研究科, 教授 (70112430)
宮縁 育夫 熊本大学, 教育学部, 准教授 (30353874)
下川 悦郎 鹿児島大学, 農学部, 教授 (60041670)
地頭 薗隆 鹿児島大学, 農学部, 准教授 (50145455)
清水 収 宮崎大学, 農学部, 准教授 (20178966)
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| Research Abstract |
A magmatic eruption event took place at Shinmoedake (Kirishima) Volcano in January 2011, leaving about 300 years of hiatus. Three subplinian explosions occurred on 26 and 27 January, which were followed by 4-day accumulation of lava at the summit crater. Vulcanican explosions were repeated from February to April, and a series of eruptions ended with phreatic explosions which occurred in June and September 2011. This eruption event was preceded by both phreatic explosions in 2008 and 2010 and elevated seismic activity in the regions surrounding Kirishima. GPS observation indicated that significant swelling of the magma chamber which located about 6 km NW of the Shinmoedake crater had continued since the end of 2009. Deflation of the magma chamber accompanied clearly subplinian explosions and the lava accumulation in the crater. The strain-meter observation showed small increases in pressure several tens of minutes prior to the subplinian explosions. Seismic array-observation during a se
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ries of vulcanian explosions showed that volcanic tremors occurred beneath the summit crater and between it and the magma chamber, supporting magma's migration from the magma chamber to the crater. The latter was confirmed by the absolute gravity measurement at the place just above the magma chamber. Inflation of the summit area, ncrease in the shallow earthquakes and decrease in the volcanic gas emitted from the crater were observed prior to the vulcanian explosions, strongly implying sealing of the conduit top preceding the explosions. It is considered that magma mixing occurred just before the eruption event because the products of the earliest stage consisted of two magmas with different compositions. The total volume of magma erupted in this event is estimated about 25 million m3, which is about 1/3 volume of the eruption 300 years ago.
During this study, we tried two times to make the eruption scenario in which sequences of eruptions are indicated, based on records of eruptions of this volcano 300 years ago and of analogous volcanoes in and outside Japan. No significant mudflows occurred in this eruption event. It is considered that the reason is that the eruption products were mainly of pumice which has high permeability of rain water. Inflation of magma chamber resumed soon after the eruptions in January 2011 and continued by the end of 2011, reaching the same level before the eruption event. It almost stopped in the beginning of 2012, suggesting a halt of the magma supply from depth. Less
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