環境トレーサーを用いたバトゥール火山火砕流斜面の地下水流動解析

抄録

Environmental tracer method was applied to investigate groundwater flow regime in the pyroclastic flow slope of Mt. Batur, Bali, Indonesia. Tracers analysed were tritium (³H) concentrations and stable isotopic compositions (δ¹⁸O) of groundwater sampled from springs and wells. Tritium concentration in groundwater depend on residence time. On the other hand, comparison of the stable isotopic compositions between groundwater and precipitation informs of recharge area of groundwater flow systems. Combined analysis of these environmental tracers and chemical quality suggested that there were two types of groundwater in the pyroclastic flow slope of Mt. Batur. One was groundwater recharged by local rainfall, and it's residence time was relatively short. The other type of groundwater indicated heavier isotopic composition than local precipitation and relatively longer residence time. Whereas, sodium and sulphate concentrations of several springs couldn't be explained by mixture of the two types of groundwater, suggesting the contribution of the leakage water from L. Batur in Batur caldera.