Cooling of the Shallow Subsurface Beneath Kuju Volcano, Central Kyushu, Japan Deduced from Geomagnetic Changes

Abstract

Repeat geomagnetic measurements were started in 1999 at Kuju volcano located in central Kyushu, Japan. Geomagnetic changes, up to more than 30nT per year, were observed, and this result shows that magnetization and cooling have taken place in the shallower part beneath Kuju volcano after the 1995 phreatic eruption and that the rates of magnetization and cooling are becoming smaller with time. Combining the results of heat discharge measurements and repeat gravity measurements, it is concluded that this magnetization occurred by the cooling of the shallower part beneath Kuju volcano by the increased meteoric water circulation.