Thermal Process beneath Active Fumarolic Areas and the Possibility of Extraction of Volcanic Heat

A Case Study at Kuju-iwoyama in Central Kyushu, Japan

Abstract

Kuju-iwoyama, the most active fumarolic area in central Kyushu, Japan, is situated at an explosive crater of Kuj u volcano. The natural heat discharge is estimated at about 100 MW and most of it (more than 95%) are from steaming grounds and fumaroles. The temperatures of fumaroles exceed 200°C and the maximum temperature is 480°C. Based on a magmatic steam-meteoric water mixing model, thermal process beneath the active fumarolic area was simulated by computer modelling. The model obtained shows the following features: high temperature magmatic steam (about 580°C and 30kg/sec) is supplied from a depth lower than 2 km. The magmatic steam mixes with the meteoric water (about 10kg/sec) in the high permeable zone (0 to 2 km depth) just beneaththe fumarolic area. The permeable zone is in a state of two-phase. A production process was simulated by extracting the fluid from the shallow part (250-500 m depth). As a result, it was concluded that the heat extraction comparable to 10 MW power generation for more than 10 years is possible without greatly affecting natural geothermal activities. The development of the two-phase reservoir beneath the active fumarolic area is a possible method to utilize volcano energy in the near future.