Quantitative Analysis of Geothermal Events at the Yoshioka Hot Spring, Aso Volcano, in 2006 Aso Volcano, in 2006

Abstract

New geothermal activities occurred at the Yoshioka hot spring of Aso Volcano from June 2006. We found a new fumarole named “a3” in a new steaming ground called “A”. The maximum temperature of the steams from it exceeded 98 degrees centigrade. In August, a vigorous fumarole “b1” and new steaming grounds “B” and “C” were formed. Vapor fluxes from these fumaroles obviously increased in October, and the daily mean heat and water discharge rates of the fumarole “b1” were estimated approximately to be 15-30MW and 6.7-13kg/s (580-1,100ton/day), respectively. Especially, “b1” ejected over 10 tons of ash on 16 October. After November 2006, the temperatures of the steaming grounds fell, and heat and the water discharge rates of the fumarole “b1” decreased to be about 4.6MW and 2.0kg/s (170ton/day), respectively. The average heat discharge rate from “b1” is more than tens times higher than that of existing natural fumaroles in the Yoshioka, Yunotani, Jigoku and Tarutama hot springs in the usual period. We infer that the vigorous geothermal events were caused by the temporal increase of vapor flux from the deep geothermal hot water.