著者

小坂 丈予 小坂 知子 平林 順一 大井 隆夫 大場 武 野上 健治 木川田 喜一 山野 眞由美 油井 端明 福原 英城

出版者

日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.31, no.2, pp.119-128, 1997

被引用文献数

7

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Geochemical study on Yugama, a crater lake at Kusatsu-Shirane volcano, has been conducted since 1966. Amounts of various cationic species in Yugama water started increasing around 1981, slightly before the phreatic eruptions in 1982-1983, and kept increasing until 1985. In 1986, they turned to decrease and at present restore their former levels before the eruptions. The concentration of sulfate ion showed a secular change similar to those of cationic species, but no such variation was observed for chloride ion even during the 1976 and 1982-1983 eruptions. However, it started increasing in 1989. A high correlation between the concentrations of chloride and hydrogen ions suggests an increasing influx of hydrogen chloride from the deep volcanic systems under the lake. A Cl^--SO₄^2- is an excellent monitor of the variation in volcanic activity at Kusatsu-Shirane volcano; all of the three past activities since 1966, i.e., the high-level subsurface activity in 1968, the eruption in 1976 and the eruptions in 1982-1983, showed a reverse secular change with time in the Cl^--SO₄^2- plot. This could be attributable to the function of Yugama water as a condenser of volatiles released underground.

著者

友寄 喜貴 棚原 朗 武村 盛久 渡口 輝 平良 初男

出版者

日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.31, no.4, pp.227-233, 1997

被引用文献数

3

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The activities of natural radionuclides, ²³⁸U, ²³⁴U, ²²⁶Ra, ²²⁸Ra, ²²²Rn, ²¹⁰Pb and ²¹⁰Po in ground waters collected from Okinawa Island were measured. The ²³⁴U/²³⁸U activity ratios in most samples showed more or less unity, whereas, relatively high values of 2.0-4.0 were obtained in samples from Motobu area. ²²²Rn activities in the ground waters were much higher than the other uranium series nuclides. The ²²²Rn/²²⁶Ra activity ratios ranged from 3000 to 29000, and those for ²¹⁰Po/²¹⁰Pb were from 0.08 to 0.82. On the whole, activities of the nuclides in the ground waters at the studied points showed higher in the order of ²²²Rn≫²¹⁰Pb>²³⁴U>²³⁸U>²²⁶Ra>²¹⁰Po. In addition to α_recoil dissolution, the selective absorption and/or desorption by some organic or inorganic substances in the aquifer may be happening.