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Hachijo Island

Sueyoshi, Hachijo city, Hachijo island, Tokyo, Japan



Phenocrysts in basalt of the Late Pleistocene (25 ka) Ishizumi Lava erupted from the Higashiyama volcano of Hachijo Island. The Ishizumi Lava is one of the eruption products by dacitic magma in the Sueyoshi stage, the last stage of the middle stratovolcano of the Higashiyama Volcano. Basalt is slightly older than the Aira-Tn volcanic ash from the Aira Caldera. The age of the Aira-Tn volcanic ash was determined by radiocarbon dating.

Hachijo Island

Outcrop of eruption products in the Sueyoshi stage of the Higashiyama Volcano. The black lava at the bottom is basalt of the Ishizumi lava. The pale brown beds on the Ishizumi lava are the dacitic Sueyoshi pumice fall deposits. The thin notched bed at the middle of the Sueyoshi pumice fall deposits is the Late Pleistocene (25 ka) Aira-Tn volcanic ash deposit. The Aira-Tn volcanic ash deposit looks black as it was notched by weathering. The Aira-Tn volcanic ash is a famous key bed covering Japan island erupted from the Aira caldera at Kyushu island.

Reported Minerals

Mineral Assemblages

  • Basalt(Host) - Forsterite - Anorthite
  • Anorthite - Copper - Zinc - Brass


  • Hachijo Island (Lava, Anorthite)
  • Miyake Island (Lava, Anorthite)
  • Hawaii (Lava, Forsterite)
  • Toge (Lava, Kaersutite)
  • Kamisano (Dike, Diposide)

Related Occurrences

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