火山 第 59 巻 ( 2014)
第 4 号 255-268 頁

論 説

南九州，池田火山の噴火史
稲 倉 寛 仁＊・成 尾 英 仁＊＊・奥 野充＊＊＊・小 林 哲 夫＊＊＊＊（2014 年 9 月 1 日受付，2014 年 10 月 16 日受理）

Eruptive History of Ikeda Volcano, Ibusuki Area, Southern Kyushu, JapanHirohito INAKURA＊, Hideto NARUO＊＊, Mitsuru OKUNO＊＊＊ and Tetsuo KOBAYASHI＊＊＊＊We made a detailed geological study to understand the eruptive history of the Ikeda volcano, which includes theIkeda caldera, maars and lava domes. The pre-caldera activity began at about 20 cal kBP with the Iwamoto ash fall
deposit. The Senta lava was also effused before the Kikai-Akahoya tephra (7.3 cal kBP). The caldera-forming eruption
began at 6.4 cal kBP with a phreatic explosion that produced the Ikezaki ash fall and surge deposits. This was soon
followed by the magmatic eruptions that produced the Osagari and Mizusako scoria fall deposits and the Ikeda pumice
fall deposit. During the climactic stage, the Ikeda ignimbrite was erupted and covered portions of the coastal area.
Immediately after the caldera-forming event, four maars were formed along the fissure vent southeast of the caldera. TheYamagawa maar, which is the largest and is located at the southeastern end of the fissure vent, erupted a pumiceous base
surge (the Yamagawa base surge), while the other maars ejected small amounts of accessory or accidental materials.
During the late stage of the Ikeda eruption, a phreatomagmatic eruption occurred at the bottom of the caldera floor,
which formed the widespread Ikedako ash fall deposit. The central lava dome was formed during the late stage of thiseruption. After the Ikedako ash fall, secondary explosions of the Ikeda ignimbrite occurred mainly along the coastalarea, generating small base surge deposits. About 2,000 years after the caldera-forming eruption at 4.8 cal kBP, newmagmatic activity began on the margin of the caldera rim, and formed the Nabeshimadake lava dome.
Key words : Ikeda caldera, caldera-forming eruption, ignimbrite, secondary explosionに求め，その海底カルデラ（早坂，1987）を阿多カルデ

1．は じ め に
南九州を南北に連なる鹿児島地溝（露木，1969）内にラとした．町田・他 (2001) は，これらをそれぞれ阿多南は，北から加久藤・小林，姶良および阿多の大型カルデ部カルデラと阿多北部カルデラとした．Fig. 1B に指宿ラが並んでおり，その南方沖には鬼界カルデラが存在す地域の代表的な火山地形を示す．阿多南部カルデラの西かく とう

こばやし

あい ら

あた

き かいる (Fig. 1A)．阿多カルデラは，Matumoto (1943) により

さつ ま

いぶすき

半分に相当する薩摩 半島南端の指宿 地域には，小型のいけ だ

105 ka（町田・新井，2003）に噴出した阿多火砕流堆積物池田カルデラ（直径約 4 km）が存在する．池田カルデラ（略称 Ata-Pfl）の分布とともに提唱された．その後，荒形成時に噴出した火砕流は西側の鬼門平断層崖と東側の牧・宇井 (1966) は，Ata-Pfl の噴出源をその北方の海域火山地域に挟まれた低地を埋め，平坦な火砕流台地を形＊〒810-0004 福岡市中央区渡辺通 1-1-1
西日本技術開発株式会社調査解析部
Survey and Analysis Department, West Japan Engineering
Consultants Incorporation, 1-1-1 Watanabe-dori, Chuoku, Fukuoka 810-0004, Japan.
＊＊〒890-0022 鹿児島市小野町 3175
鹿児島県立武岡台高等学校
Takeokadai Senior High School, 3175 Ono-machi,
Kagoshima 890-0022, Japan.
＊＊＊〒814-0180 福岡市城南区七隈 8-19-1
福岡大学理学部地球圏科学科・産学官連携研究機関
国際火山噴火史情報研究所
Department of Earth System Science, Faculty of Science,

おんかどびらalso AIG Collaborative Research Institute for International
Study on Eruptive History and Informatics (ACRIFISEHAI), Fukuoka University, 8-19-1 Nanakuma, Jonanku, Fukuoka 814-0180, Japan.
〒890-0065 鹿児島市郡元 1-21-35
鹿児島大学大学院理工学研究科地球環境科学専攻
Department of Earth and Environmental Sciences, Graduate
School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan.
Corresponding author: Hirohito Inakura
e-mail: h-inakura@wjec.co.jp