Construction of late Quaternary eruption history in and around the Izu Volcanic Islands, off Tokyo
We have recognized 21 eruptive events at least on Niijima Volcano, and some of them are derived from Kozushima and other distal volcanoes during late Quaternary. Kozushima Volcano, based on previous studies, would have erupted extensively basement lavas and overlying pyroclastic deposits at 70-64 ka, 52-35 ka, 32-23 ka. After that, we recognized 8 eruptive events at least on the Kozushima Volcano, and some of them are correlated to tephras from Niijima and other distal volcanoes.
The felsic maker tephras provided from Niijima and Kozushima volcanoes are also found at Izu-Oshima and Toshima volcanoes. The Izu-Oshima Volcano has a record of 12 major eruptions occurred after 1.8 ka, which were the caldera-forming activity. We re-examined the chronological framework based on 14C dating of eruption history of the Younger Edifice of pre-caldera before 1.8 ka. As a result, eruptive frequency of Izu-Oshima from 17 ka to 1.8 ka is shorter (67–75%) than previous estimation, suggesting higher frequent occurrence of the eruptions in this period.
Also, we investigate tephrostratigraphy in the marine core which length is 190.38 m off the Boso Peninsula. The upper 30 m of this core includes felsic tephras provided from Niijima, Kozushima, and Omurodashi volcanoes since 20 ka.