| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
The aim of this research was to define the following issues on cold spring of active volcanoes by means of isotope-hydrology and hydro-geochemistry ; (1)Is it found that magnetic CO_2 dissolves in volcano spring waters?, (2)If we find such springs, what geological structure will limit the spring distribution?, (3)How much is total flux of magmatic CO_2 discharged from such springs? In the term of this project, we had investigated active volcanoes in central Kyushu, Japan : Kuju, Aso and Unzen Volcanoes.
From chemical and isotopic analyses of shallow groundwater samples from 90 cold springs in Kuju Volcano, it was found that spring waters dissolving much magmatic CO_2 distribute around the youngest volcanic edifices : Mt.Taisen and Mt.Kuro-dake, which were formed several thousand years ago. Such specific distribution also can be seea in Unzen Volcano ; the distribution of magmatic CO_2-dissolved spring waters are concentrated around Mt. Mayu-yama formed about 4000 years ago. Total fluxes of magmatic CO_2 discharged from such spings of both volcanoes were estimated to be about 10 tons per day.
In contrast with above two volcanoes, we could not detect magmatic CO_2 from shallow groundwater samples from 60 cold springs of Aso Volcano. This result suggests that the magmatic CO_2 supply system to groundwater in Aso Volcano might be differs from that of Kuju and Unzen Volcanoes. As it was expected that CO_2 escaping from magma chamber or magma conduit would be supplied to deep groundwater systems, we carried out an extra chemical and isotopic analyses for groundwater samples from 22 wells of 200m-1300m deep in Aso Volcano in the same way of the spring investigation. The obtained data show that as depth of well becomes deeper, the groundwater contains more much magmatic CO_2.
This research brought unexpected instructive information that there would be more than one magmatic CO_2 supply system to groundwater in active volcanoes.
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