We describe here a first attempt to estimate the water seepage rate of an active crater lake using radioactive cesium dispersed into the environment by the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011 as a hydrological tracer. Kusatsu-Shirane volcano is one of the most active volcanoes in Japan and has an active crater lake named Yugama. There is no outflow such as a river from Yugama crater lake. The content level of stable cesium (133Cs) in Yugama water was almost constant at 15-20 nM during the sampling period of Nov. 2011 to Nov. 2014. In contrast to 133Cs, however, the radioactive cesium (134Cs and 137Cs) concentrations in Yugama water decreased at a more rapid rate than expected by radioactive decay. Based on the decreasing rates of activity concentrations of 134Cs and 137Cs in Yugama water during the three years between 2012 and 2014, it is estimated that 700-800 m3 of the Yugama water, which corresponds approximately to 0.1% of the total volume, leaks through the lakebed per day. In the estimation, balance between leakage of radioactive cesium contaminated water though lake bed and geothermal inflow of radioactive cesium-free water in the volcano was taken into account. Consequently, the water seepage rate of the Yugama crater lake was calculated to be 8.1-9.3 L s-1.

中文翻译：

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使用FDNPP衍生的放射性铯作为水文示踪剂，估算日本草津-平野火山活火山湖系统中的渗水率。

我们在这里描述了首次尝试，是利用2011年3月福岛第一核电站事故作为水文示踪剂而散布到环境中的放射性铯来估算活火山口湖的渗水率。草津-史拉尼火山是日本最活跃的火山之一，有一个活跃的名为Yugama的火山口湖。没有从尤加马火山口湖流出的河。在2011年11月至2014年11月的采样期间，汤加马水中稳定铯（133Cs）的含量水平几乎恒定在15-20 nM。但是，与133Cs相比，放射性铯（134Cs和137Cs）的浓度与133Cs相反Yugama水以比放射性衰变预期更快的速度下降。根据2012年至2014年这三年间汤加玛水中134Cs和137Cs的活动浓度下降的速率，估计有700-800立方米的汤加马水泄漏，约占总体积的0.1％，通过每天湖床。在估算中，考虑了放射性铯污染的水通过湖床泄漏与火山中放射性无铯水的地热流入之间的平衡。因此，Yugama火山口湖的渗水率经计算为8.1-9.3 L s-1。考虑到放射性铯污染的水通过湖床泄漏与火山中放射性无铯水的地热流入之间的平衡。因此，Yugama火山口湖的渗水率经计算为8.1-9.3 L s-1。考虑到放射性铯污染的水通过湖床泄漏与火山中放射性无铯水的地热流入之间的平衡。因此，Yugama火山口湖的渗水率经计算为8.1-9.3 L s-1。