火山性温泉

抄録

High temperature sodium chloride waters have been reported in many of active geothermal field developed in the central part of some Japanese Quarternary volcanoes such as Hakone, Onikobe, Kuttara, and Kuju. Many of micro-earthquakes occur in those active geothermal field, showing intimate relation between micro-seismic activity and strong geothermal activity. Provided the phase transformation of thermal waters to steam is the major cause for such types of volcanic micro-earthquakes, the chemistry of sodium chloride waters permits to estimate the temperature-pressure condition at depths where seismic activity takes place. The vapor-dominated system suggested by White et al. (1971) is an important concept to understand the distribution of acid sulfate waters at shallow depth in contrast with the development of hot water system characterized by neutral to alkaline sodium chloride waters at greater depth of the volcanic geothermal field.