2018 Fiscal Year Final Research Report
Relationship between geological structure and chemical characteristics of hot springs around Aira caldera
| Project/Area Number |
16K17822
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Multi-year Fund |
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| Research Field |
Geology
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| Research Institution | Kagoshima University |
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Principal Investigator |
Kawabata Kuniyo 鹿児島大学, 理工学研究科, 特別研究員 (10773468)
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| Research Collaborator |
Kazahaya Kohei
Morikawa Noritoshi
Tsunomori Fumiaki
Tomiyasu Takashi
Takahashi Hiroshi
Takahashi Masaaki
Kodamatani Hitoshi
Kitamura Yujin
Kano Kazuhiko
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | 姶良カルデラ / 温泉 / 断層 / ヘリウム同位体比 / マグマ |
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| Outline of Final Research Achievements |
Aira caldera located in the Kagoshima Bay is likely to have a large magma chamber, supplying magma to active volcanoes Sakurajima and Wakamiko in the caldera. Around Aira caldera, there are many hot springs which are presumed to be affected by the volcanic activity. We tried to clarify relationship between geological structure and chemical component of hot springs gas and water, especially focusing on helium isotopes ratio. We sampled 24 hot springs water and analyzed stable hydrogen and oxygen isotopes ratio, helium isotopes ratio, dissolved ions and radon isotope concentration. The results show that most of all hot springs is meteoric water origin. The hot springs including mantle helium was recognized only at northern and southern region of the caldera. The distribution is also related to fault distribution formed by Kagoshima rift activity. These results suggest that mantle originated gas is upwelling through the faults associated with Kagoshima rift.
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| Free Research Field |
地球化学
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| Academic Significance and Societal Importance of the Research Achievements |
鹿児島湾を形成する姶良カルデラは活火山桜島と若尊を有する巨大カルデラであり，周囲には温泉が多数湧出している．温泉成分の分析と地質調査から，温泉がどのように形成されたのか，マグマとどのように関わり持つのかを調査した．分析・調査結果から，温泉の特徴は地質構造によって大きく規制されており，着目する点として鹿児島地溝に関係する断層方向に沿ってマントル由来のヘリウムが含まれる温泉が分布する事が挙げられる．鹿児島湾では地下深くから断層の裂け目を通ってガスが上昇し水と混じり温泉が形成されている．今後これらの温泉をモニタリングする事でマグマ活動など地下の変化を検出できる可能性が開かれた．
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