2001 Fiscal Year Final Research Report Summary
| Project/Area Number |
11680470
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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 |
Natural disaster science
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| Research Institution | Kyoto University |
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Principal Investigator |
OHSAWA Shinji Graduate School of Science, Associate Prof., 理学研究科, 助教授 (30243009)
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| Co-Investigator(Kenkyū-buntansha) |
YUSA Yuki Graduate School of Science, Prof., 理学研究科, 教授 (90025403)
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| Project Period (FY) |
1999 – 2001
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| Keywords | volcano / fumarolic gas / mixing / magmatic gas / air / underground water / vadose zone / flow rate |
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| Research Abstract |
There have had numerous discussions of source components in the volcanic fumarolic gas in different volcanoes, but most of the questions about the mixing process and the mixing mechanism of the discharged fumarolic gas remain unconcerned. The purpose of this study is to improve the understand in the mixing process and the mixing mechanism of volcanic fumarolic gas with respect to the geochemical and geophysical standpoints.
From the quantitative estimation by means of the δD and δ^<18>O values and the He/Ar ratios of the fumarolic gases from Kuju-Iwoyama fumarolic area of Kuju Volcano, Japan, the proportion of mixing for the three end-members: magmatic fluid_<(g)>, air_<(g)>, ASW_<(l)> was estimated to be 1 : 0.0005-0.0021 : 0.0009-0.0043. This relative proportion and a linear relationship between the δ-values (δD and δ^<18>O) and the He/Ar ratios of the fumarolic gases indicate that the fumarolic fluid would be formed by the mixing of the vadose fluid (vadose air and vadose water) and
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the magmatic fluid into the fumarolic gas conduits within the vadose zone. This mixing model will reasonably explain the contradiction in terms of the isotopic and chemical data of fumarolic steams and gases from Satsuma-Iwojima Volcano and from Kuju-Iwoyama between 1959 and 1984; δD and δ^<18>O of steam condensates show the typical values of andesitic magmatic steam, whereas He/Ar ratios of fumarolic gases clearly indicate the mixing of air and/or ASW into magmatic fluid.
We try to set a dynamic model for the advanced understanding the mixing mechanism of the vadose fluid into the magmatic fluid, based on the geophysical observations and the geochemical data. There is a good linear relationship between the discharge velocity of the fumarolic gas and the mingling volume of vadose air into the fumarolic gas conduit calculated by the mass flow rate and the relative proportion of the mixing of vadose fluid in the fumarolic gas. This linear relationship can be perfectly explained as the suction of vadose fluids into fumarolic gas conduit should accompany with flowing of volcanic fluid in the gas conduit. A cylindrical-shape fumarolic gas conduit model can explain the physical phenomenon in which the volcanic fluid flow with the higher speed in fumarolic gas conduit coupled with more vadose fluids component in the fumarolic gas. Less
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