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Kuju Iwo-yama is one of the most active fumarolic sites in Kyushu, last erupting in 1995, and is located at about 1,500 m above sea level on the northeastern slope of Mt. Hossho-zan (1,678 m). The site is 4 to 5 km to the southeast of the Otake-Hatchobaru water-dominated geothermal field. Condensates from fumaroles produce strongly acid Cl-SO4-type water with isotopic signatures indicating a magmatic origin. Advanced argillic alteration and sublimation of sulfur are significant at the fumarolic site. Here we can observe thermal manifestations of the modern analogue to high-sulfida- tion activity and compare them with the water-dominated Otake-Hatchobaru geothermal systems just kilometers away.

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