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.