There are huge volume and good quality groundwater in volcanic fields, therefore the volcanic fields are estimated as suitable water resource area. However, because geological structures of aquifer in volcanic fields are often heterogeneous, it is not easy to estimate groundwater distribution and groundwater flow path easily. Therefore, it is difficult to predict water quality degradation and depletion of water resource by anthropogenic activity such as welling, tunneling and agricultural activity. It is too expensive to use isotope tracer to assess the impact of anthropogenic activity to groundwater resources. If the temperature, pH, EC, Eh and ion concentrations can predict the change of groundwater conditions, is become easy to assess the groundwater condition changes by anthropogenic activity. Therefore, we try to understand the relationship between volcanic geology and groundwater chemistry at Yotei Volcano at Hokkaido, Northern Japan.
Hydrogen and oxygen stable isotope ratios show that all groundwater in Yotei Volcano is derived from meteoric water. The groundwaters on Yotei Volcano were classified into five groups base on geochemical analysis and hierarchical cluster analysis (HCA). Principal Component Analysis (PCA) shows that water-rock interaction is most advanced in groundwater in several lava flows presumably composed of basalt and low-flow rocks, followed by groundwater upwelling from fine-grained pyroclastic rocks and debris avalanche deposits. From PCA, the geochemical process at some springs seems to organic matter decomposition and anthropogenic pollution.
