Studies1

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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 interiors of volcanoes feature extreme temperatures of over 1000 degrees centigrade, and volcanoes that discharge large amounts of heat are defined by complex thermal processes. We can contribute to the prediction of volcanic eruptions, the mitigation of volcanic disasters and the utilization of volcanic energy by clarifying the thermal processes of volcanoes. Laboratory Geothermics at Kyushu University is working to elucidate the thermal processes of the Mt. Kuju volcano in central Kyushu in Japan.

DETAILED:
The Mt. 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 fumarole field called Kuju Iwoyama is in the central part of Kuju, and displays the most intensive geothermal activity in Japan. The Laboratory of Geothermics at Kyushu University has been conducting geophysical observations of volcanic activity for over thirty years. As a result, the thermal processes beneath the volcano have been clarified, and we have contributed to the prediction of volcanic eruptions, the mitigation of volcanic disasters and the utilization of volcanic energy. We have a molten magma reservoir at a depth of 7 km, and the magmatic fluids (mainly H2O) mix with the infiltrating meteoric waters at a depth of 2 km. 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. Our geophysical observations detected anomalous precursor phenomena in the 1980s and we predicted the occurrence of a volcanic eruption in the early 21st century. The phreatic eruption began in October 1995. Our geophysical monitoring then observed a cooling of the volcanic body, which was accurately simulated numerically. A study of the thermal processes verified that Kuju contains a large amount of thermal energy, and we proposed a new technique called Down-Hole Coaxial Heat Exchange (DCHE) to extract heat from a deeper part of the volcano. The Laboratory of Geothermics at Kyushu University is still working to clarify more detailed thermal processes, to reduce the damage caused by volcanic activity, and to expand volcanic energy resource use 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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