Estimation of groundwater quality forming mechanism in Kuju volcano based on principal component analysis and stable isotope rations

Abstract

The volcano stores a large amount of groundwater in the mountain body. Because the heated water coming from a magma activity around a volcano is rise from deeper ground, chemical variety is recognized in groundwater and heated water. On the other hand, it is assumed by experiments and simulations that the groundwater chemistry is controlled by water-rock interaction between groundwater and rocks neighboring. Therefore, it is necessary to consider water - rock interaction for examination of the quality of the water formation. Furthermore, the influence by the magma activity must be considered in the volcano area. The Kuju volcano is an active volcano located in a volcanic front of Middle Kyushu and the Beppu - Shimabara rift valley. Various springs exist around the Kuju volcano, but the water quality formation mechanism as a whole is not examined. Therefore, this study clarifies a characteristic of the springs and the heated waters around this volcano and examines water - rock interaction in this volcano area. And it is intended to clarify it about the water quality formation mechanism of the whole Kuju volcano based on them. We performed the quality of the water analysis of the sample, and principal component analysis based on the result. Moreover, a stable isotope rations of water samples were analyzed. It is thought from the results of the principal component analysis that the quality of the water which is rich in Ca and Mg was formed by water-rock interaction with the andesite, and that the quality of Na and K rich water is caused by water-rock interaction with dacite. Furthermore, it is thought that the origin of the groundwater is rainfall from the result of the isotope analysis.