| Title | Drastic Change of Thermal State Beneath an Active Fumarolic Field Before and After the 1995 Phreatic Eruption of Kuju Volcano, Japan |
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| Authors | R. Ohki, S. Ehara, K. Fukuoka, & S. Taguchi |
| Year | 2003 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | |
| Abstract | We have conducted two shallow drilling experiments at Kuju-Iwoyama fumarolic area in 1991 and 2001. Prior to the drilling in 1991, several geophysical surveys were Carried out, and a high resistivity anomaly was detected. This resistivity anomaly represented the superheated steam reservoir. We dug a short directional borehole and succeeded in obtaining superheated steam at a temperature of 233 "C at the wellhead. In 2001, we dug another borehole toward the deeper part of the reservoir, but the temperature of the steam was 98 "C. To investigate the reason of the cooling of the reservoir, another resistivity survey was carried out. The inverted resistivity model implied that the superheated reservoir had cooled and liquefied. This drastic change of the thermal state beneath the fumarolic area shows one aspect of the cooling process after the phreatic eruption which occurred in 1995. The change in resistivity showed good agreement with other geophysical observations, such as magnetic and gravity changes. |