A large self‐potential anomaly on Unzen Volcano, Shimabara Peninsula, Kyushu Island, Japan

Abstract

Self‐potential (SP) observation was carried out in the summit area of Unzen, one of the active volcanoes in Kyushu island, Japan. We found a positive SP anomaly in the vicinity of the newly extruded lava dome. The potential difference across the anomaly exceeds 1000mV per 500m. Streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly. In association with the first emergence of the lava dome a sharp increase of SP was detected, which is considered to be a result of the growth of the hydro‐thermal system. Copyright 1995 by the American Geophysical Union.