Volcanoes generally have a large water storage capacity and hold many springs, so the groundwater flow system in volcanic areas plays an important role in hydrology. In order to investigate the hydrological circumstances of volcanic water, we collected groundwater flowed out at ～1200m above sea level at Daisen Volcano, Tottori, Japan from Apr. 2000 to Jan. 2002 and measured 87Sr/ 86Sr ratio and concentrations of dissolved ions (Na+, K+, Mg2+, Ca2+, Sr2+, Cl-, NO3- and SO42-) in the samples together with analyses of its reservoir rock and precipitation.
Concentrations of cations (particularly alkaline earth metals) in Daisen groundwater samples are systematically higher compared to those of precipitation of Yonago City (adjacent location) though anion concentrations substantially remain unchanged. The results also indicate relatively constant 87Sr/86Sr ratios, ranging from 0.70519 to 0.70525, which are similar to those of the reservoir rock (dacite; 0.70512, 0.70516). On the other band, precipitation sampled in the same seasons at Tottori City shows 87Sr/86Sr ratios (0.70886～0.71044) much higher than those of Daisen groundwater. From these results, we suggest that the dissolved metal species and Sr isotopes in Daisen groundwater were not originated from precipitation but produced basically by water/bedrock interaction during the migration of water.
In addition, the preliminary approach of low background γ-ray spectrometry was also carried out for Daisen groundwater. It was found that the activity of 22Na (t1/2 = 2.6y) was below the detection limit of our measurement (<～3✕10-4dpm/l) suggesting that the residence time of the ground water is >10 years.