Formation process of Na-Cl type thermal water distributed in Hakodate area

Abstract

In this study, formation process of thermal water in Hakodate area was discussed by analyzing the major dissolved chemical components, stable isotope ratios of hydrogen and oxygen, and trace element concentrations such as Li and B. As a result, most of the thermal waters were Na-Cl type and were diluted by fresh water. It was estimated that the thermal waters distributed in the coastal areas were formed by direct intrusion of present seawater or by diagenetic alteration of paleo seawater trapped in the strata. For thermal waters in the area with a geothermal gradient of 3.0-79.4°C, both of the intrusion of present seawater and the water-rock interaction at high temperatures would be related to the formation process.