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Study of Thermal Processes Beneath Volcanoes and Their Application to Eruption Prediction and Energy Use

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Mt. Kuju volcano just after the 1995 eruption


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Cooling of the Mt. Kuju volcano
after the 1995 eruption as shown
by numerical simulation.
Top: Before the 1995 eruption,
Bottom: 10 years after the 1995 eruption.


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Concept of thermal energy
extraction from a volcano

ABSTRACT:
The deep interior of volcanoes shows very high temperature over 1000 degree C and volcanoes discharging a large amount of heat show complicated thermal processes. We can contribute to prediction of volcanic eruption, mitigation of volcanic disaster and utilization of volcano energy by clarifying the thermal processes of volcanoes. Laboratory Geothermics, Kyushu University has been trying to elucidate the thermal processes of Kuju volcano in central Kyushu, Japan.

This research fund is Grant-in-Aid for Young Scientists (S) (No. 21676007) by Japan Society for the Promotion of Science.

DETAILED:
Kuju volcano is situated in the southwestern part of Oita Prefecture in central Kyushu, Japan. Phreatic eruptions occurred in October and December, 1995. We have four geothermal power plants at the foot of Kuju volcano and the total installed capacity is 154.5MW. The Kuju volcanic region is the largest geothermal power generation zone in Japan. An active fumarolic field called Kuju Iwoyama is in the central part of Kuju volcano and show the most intensive geothermal activities in Japan. Laboratory of Geothermics, Kyushu University has been conducting geophysical observations of volcanic activities over thirty years. As the results, the thermal processes beneath the volcano were clarified and we contributed to prediction of volcanic eruption, mitigation of volcanic disaster and utilization of volcano energy. We have a molten magma reservoir at 7 km depth and the magmatic fluids (mainly H2O) mix with the infiltrating meteoric waters at 2km depth. We have a two-phase (steam-liquid mixture) volcanic geothermal reservoir between the surface and the 2km depth, and steam and hot spring water are discharged at the surface. The geophysical observations detected anomalous precursor phenomena in 1980s and predicted the occurrence of volcanic eruption in the early 21 century. The phreatic eruption began in October, 1995. Laboratory of Geothermics, Kyushu University has been conducting geophysical monitoring of volcanic activities and contributed to mitigation of volcanic disaster. Cooling of the volcanic body was observed and was simulated numerically very well. The study of the thermal processes showed that Kuju volcano has a large amount of thermal energy and we proposed a new technique called Down-hole Coaxial Heat Exchanger (DCHE) to extract heat from the deeper part of the volcano. Laboratory of Geothermics, Kyushu University is still trying to clarify the detailed thermal processes and to contribute to mitigation of volcanic disaster and utilization of volcano energy in the future.

Laboratory of Geothermics,
Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University
Professor Yasuhiro Fujimitsu
Associate Professor Takeshi Tsuji
Associate Professor Jun Nishijima
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