TrekGEO > Mineral Trail > Kanto region > Gunma pref. > Manza-Karafuki

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Hoshimata, Tsumagoi city, Agatsuma county, Gunma pref., Japan


Fumarole deposit

Sulphur deposit around an active fumarole. Volcanic gas released from the fumarole at the andesite fissures of the early Pliocene (5 Ma) Takai Lava. The Takai Lava distributes at high altitute area in the western half of Mount Kusatsu-Shirane, and underlies the Middle Pleistocene (0.6 Ma) lavas of Mount Kusatsu-Shirane in the eastern half. Mount Kusatsu-Shirane was active in the Middle Pleistocene (0.6-0.3 Ma) and has been active since the Late Pleistocene (16 ka).


Outcrop of an active fumarole. The fissure releasing white gas is fumarole. The gray host around the fumarole is andesite of the Takai lava. The yellow beds are sulphur. Note that no plants grow near the fumarole as it releases toxic hydrogen sulfide. Sulphur was formed by reacting H2S in volcanic gas with O2 in air:

2H2S (Hydrogen sulfide) + 3O2 >> 2H2O + 2SO2

SO2 + 2H2S >> 3S (Sulphur) + 2H2O

Reported Minerals

  • Sulphur


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