Explanation of volcanic activity by detailed terrace chronology and crustal deformation observation in Io To Island in Ogasawara Archipelago

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We carried out detailed chronological study on the coastal terraces in Io To island, in Ogasawara Archipelago. By means of<14>^C radiocarbon dating on the fossils of coral and carbonized wood, we estimated the history of the terrace formation, which shows the uplift of Io To Island should be intermittent, not be constant as suggested in the former study(Kaizuka et al, 1985). Recent uplift observed by GPS survey is so rapid that it could be comparable to the remarkable uplift about 500 years ago, when Mt. Motoyama upper terrace was formed, accompanied by the eruption of Mt. Suribachi-yama. This notable crustal deformation suggests following volcanic activities. We can propose a model that notable uplift by the possible magma intrusion would occur before the remarkable volcanic activity of Io To islands, from this study.