伊豆諸島における9世紀の活発な噴火活動について : テフラと歴史史料による層序の改訂

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Based on the study of tephra deposits and historical documents concerning with Izu islands, we reexamined the volcano-stratigraphy in and around Izu islands. We reconfirmed that Kozushima Tenjosan erupted in A.D.838 and Niijima Mukaiyama erupted in A.D.886. Eruptions from both volcanoes were big throughout their eruptive histories. Dispersed tephras from these eruptions covered most of the Izu islands, thus are good time-markers. Our results revealed that the several eruptive events occurred in between the A.D.838 and A.D.886 major volcanic episodes. In Izu-Oshima, the later stage of N3.0, N2.0 and N1.0 eruptions took place. In Niijima, a series of eruptions started with phreatomagmatic eruption of basaltic composition at Kudamaki and ended with the formation of Atchiyama rhyolite dome. In Miyakejima, lavas were effused from Oyama central vent which spilled over Hatchodaira caldera. A lateral fissure extended from the eastern flank to Miike and resulted in a phreatomagmatic eruption around A.D.850. We concluded that the volcanism during the middle of the 9th century in and around Izu islands was unusually high compared with the eruptions of both the preceding and the following periods.
特定非営利活動法人日本火山学会の論文
2006-10-31