著者

筒井 正明 小林 哲夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.1, pp.21-30, 2022-03-31 (Released:2022-04-26)

参考文献数

37

---

Ohatayama and Ohataike are adjacent volcanoes aligned in NE-SW direction at the northeastern portion of Kirishima Volcano Group, Kyushu, Japan. Ohatayama volcano has three small craters around the summit area, and Ohataike has a summit crater lake with a diameter of 400 m. Both volcanoes are composed mainly of tephra fall deposits by plinian or sub-plinian eruptions, with intercalations of pyroclastic flow deposits. The main volcanic edifice of the highest point of Ohatayama volcano was formed at least 22 cal ka BP. Tsukiyama were formed earlier than the highest point, and there is a possibility that they can be separated from the highest point. The triangulation point of Ohatayama volcano started its activities on the highest point somewhere around 17-11 cal ka BP, and forming craters A and B. Ohataike volcano was formed by erupting again around 17-11 cal ka BP, after the main volcanic edifice was formed during around 22-17 cal ka BP on the northeast side of the triangulation point. This was followed by four different modes of eruption at Ohatayama C crater in the following order: a phreatic eruption (Oy-4) in 7.6 cal ka BP, Ohatayama lava emission, magmatic and phreatic eruptions (Oy-3) in 7.1 cal ka BP, magmatic and phreatic eruptions (Oy-2) in 6.8 cal ka BP, and lastly, phreatic eruption (Oy-1) in 6.5 cal ka BP. Although no volcanic activity occurred from Ohataike volcano since 11 cal ka BP, foamy volcanic gas is currently being detected on the surface of the crater lake.

著者

筒井 正明 奥野 充 藤沢 康弘 小林 哲夫 Tsutsui Masaaki Okuno Mitsuru Fujisawa Yasuhiro Kobayashi Tetsuo

出版者

福岡大学研究推進部

雑誌

福岡大学理学集報 = Fukuoka University Science Reports (ISSN:0386118X)

巻号頁・発行日

vol.49, no.2, pp.89-97, 2019-09

著者

及川 輝樹 筒井 正明 大學 康宏 伊藤 順一

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.57, no.4, pp.199-218, 2012-12-28 (Released:2017-03-20)

参考文献数

65

---

Shinmoedake (Kyushu, Japan), which is one of the Kirishima Volcanoes, experienced several small eruptions in 2010, finally culminating in a sub-plinian eruption on January 26-27, 2011. After this sub-plinian phase, the eruption style shifts to the phase of vulcanian eruption or ash emission. This volcanic activity is still occurring. We here summarize the eruption history of Shinmoedake during the Edo period on the basis of historical records. The eruptions of Shinmoedake during the Edo period occurred in AD 1716-1717 (Kyoho eruption) and AD 1822 (the 4th year of Bunsei eruption). The Kyoho eruption, which was a large-scale (total amount of tephra: 2×1011 kg) eruption, is divided into the following seven stages. Stage 1 (Apr. 10, 1716 to May 7, 1716): small eruptions occurred over two months; Stage 2 (Sep. 26, 1716): falling ash first observed at the foot of Shinmoedake; Stage 3 (Nov. 9 to 10, 1716): the first large eruption was observed, with pumice falling over a wide area; Stage 4 (Dec. 4 to 6, 1716): small eruptions; Stage 5 (Feb. 9 to 20, 1717): the second pumice fall eruption, with an intermittent ash fall eruption thereafter; Stage 6 (Mar. 3, Mar. 8, Mar 13, Apr. 8, 1717): ash fall eruptions; Stage 7 (Sep. 9, 1717): the last ash fall eruption. These eruptions, which continued intermittently over 17 months, were characterized by multiple repetitions of a large eruption. Based on the results of a comparison between the Kyoho eruption and the 2011 eruption, the eruptions from March 30, 2010 to January 26, 2011, were similar to Stages 1 to 3 of the Kyoho eruption; the eruptions after January 26, 2011, were similar to Stages 5 to 6 of the Kyoho eruption. In addition, the relatively large eruption events of Stages 3 and 5 of the Kyoho eruption and the January 26-27, 2011, eruption began without any noticeable precursors. The eruption in the 4th year of Bunsei (AD 1822) was a small eruption that lasted less than a day. The recent eruption sequences, which were also similar to the Edo period eruptions, are divided into a small-scale eruption (the 1959 eruption) and a large-scale eruption (the 2011 eruption). The eruption duration time of the small-scale (total amount of tephra: < 1010 kg) eruption was less than a day. The eruption duration time of the large-scale (total amount of tephra: > 1010 kg) eruption could be a few months or years. Both eruption sequences began with a small eruption. A large-scale eruption can occur a few months after the start of the eruption sequence. This is an important turning point in the eruption sequence of Shinmoedake.