Self-potential measurement and experimental study related with thermal process of volcano

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1.Self-potential (SP) surveys were conducted on six active volcanoes : Usu-san, Hokkaido Komage-take, Miyake-jima, Tarumae-san, Me-akan-dake and Esan. Large and positive SP anomalies, in both spatial extent (1-2 km) and magnitude (several hundred mV), were observed on the high ground temperature zones of the former for volcanoes. The anomalies are mainly caused by electro-kinetic effect due to the upwellingof the hot ground water triggered by the remnant magma situated at the shallow depth. On the other hand, no significant SP anomaly was observed on the latter two volcanoes, suggesting the hydrothermal circulation of large size has not developed within the edifices. Considering the hot volcanic gas had ejected from the summit crater, it is speculated that the volcanic activity of the both volcanoes is vapor-dominated : vapor cannot transport the electric charge.2.In order to quantify the SP anomalies in volcanic regions, the field experiment for measuring the in-situ value of the electrokinetic coupling coefficient was made at Atosanupuri-Kawayu district at where the underground hydrological model, such as the flow pass, the amound of flow and so on, has been established. The estimated value was well correlated with the results of the laboratory experiments by other scientists.