| Project/Area Number |
09640524
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | Okayama University of Science (1999)
Kyoto University (1997-1998) |
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Principal Investigator |
KITAOKA Koichi Fac. Sci., Okayama University of Science, Prof., 理学部, 教授 (30093230)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAGUCHI Kazuhiro Fac. Sci., Okayama University of Science, Lect., 理学部, 講師 (20239883)
OHSAWA Shinji Fac. Sci., Kyoto Univ., Okayama University of Science, Assoc. Prof., 大学院・理学研究科, 助教授 (30243009)
YUSA Yuki Fac. Sci., Kyoto Univ., Okayama University of Science, Prof., 大学院・理学研究科, 教授 (90025403)
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| Project Period (FY) |
1997 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1999: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Keywords | Active volcano / Meteoric water / Magmatic water / Stable isotopes / Tritium / Steam water / Critical temperature / Kuju-lwoyama volcano / 湧水 / 温泉水 / 河川水 |
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| Research Abstract |
Fumarolic steam of high isotopic ratios of deuterium and oxygen-18, which is regarded as magmatic water, had been measured around 1960 at Kuju-lwoyama volcano, central Kyushu, Japan. After that, the isotopic ratios of fumarolic steam had been gradually failing during several decades before the 1995 phreatic eruption.
Isotopic contents of fumarolic steam and hot spring water in the fumarolic area before the eruption suggest that part of meteoric water infiltrates deeply under the volcano with accompanied steam separation and reaches to the critical point of water. The super-critical meteoric steam could mix with magmatic steam originated from deep.
Tritium contents of fumarolic steam show that a relatively short residence time of meteoric water within around 5 years in the steam system in the volcano, indicating a rapid mixing between magmatic fluids and meteoric steam. However, tritium contents of hot spring water in the fumarolic area suggest a very long residence time of liquid meteoric water over one century. These indicate that the steam system in the volcano is the main system of meteoric water circulation, while the liquid water circulation system is very slow only as a sub-system.
The decrease of magmatic water content in fumarolic steam during several decades before the eruption may be owing to the change of conduit permeability of magmatic steam at deep zones. The permeability reduction causes the pressure depression of magmatic steam moving upward in the shallow zones. If the pressure of magmatic fluids falls lower than the critical pressure of water, meteoric steam in two-phase zones formed around the magmatic fluids conduits can enter the conduits and mix with magmatic water.
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