| Project/Area Number |
63041090
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| Research Category |
Grant-in-Aid for Overseas Scientific Survey.
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| Allocation Type | Single-year Grants |
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| Section | Field Research |
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| Research Institution | Okayama University |
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Principal Investigator |
KUSAKABE Minoru Institute for Study of the Earth's Interior, Okayama University, 地球内部研究センター, 教授 (20015770)
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| Co-Investigator(Kenkyū-buntansha) |
SHINOHARA Hiroshi Department of Chemistry, Tokyo Institute of Technology, 理学部, 助手 (30196406)
NOJIRI Yukihiro National Institute for Environmental Studies, 総理府技官 (10150161)
SATO Hiroaki Faculty of Integrated Arts and Sciences, Hiroshima University, 総合科学部, 助教授 (60019495)
HIRABAYASHI Jun-ichi Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, 草津白根火山観測所, 助教授 (30114888)
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| Project Period (FY) |
1988 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥9,600,000 (Direct Cost: ¥9,600,000)
Fiscal Year 1989: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1988: ¥9,000,000 (Direct Cost: ¥9,000,000)
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| Keywords | Lake Nyos / Cameroon / gas disaster / magmatic origin / bathymetry / flux of heat / CO_2 flux / disaster prevention |
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| Research Abstract |
Outburst of a large amount of CO_2 dissolved in Lake Nyos, Cameroon, killed more than 1700 people on 21 August 1986. The surveys made soon after the gas disaster indicate that the CO_2 is of magmatic origin and the lake is chemically stratified. We revisited the lake in December 1988. Our bottom sounding study revised the bathymetry by Hassert (1912). The conductivity-temperature-depth profiller (CTD) measurements and chemical analysis of the lake water revealed that temperature, total dissolved solids (TDS) and CO_2 content of water below 160 m increased considerably over the last 25 months. This supports the view that CO_2 is being supplied to the lake bottom in the form of warm, CO_2-charged, mineralized water. Fluxes of heat and CO_2 were estimated to be 0.36 MW and 515-560x10^6 mol/y, respectively. The CO_2 flux is consistent with that estimated from the He-T relationship. The CO_2 flux is large enough to saturate the lake's hypolimnion within 50 y. Using the CO_2-TDS-Si relationship and temperature dependence of amorphous silica solubility, chemical composition of the warm mineralized water was estimated. Existence of a CO_2-saturated fluid below the sedimentary cover is suggested. These are the important findings for disaster prevention.
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