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

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<sup>-</sup>-SO<sub>4</sub><sup>2-</sup> 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<sup>-</sup>-SO<sub>4</sub><sup>2-</sup> plot. This could be attributable to the function of Yugama water as a condenser of volatiles released underground.