Abstract
Additional data on the volcanic activity of Izu-Oshima is presented based on the detailed stratigraphic study of the Older Oshima Group in the southern part of the island. 1. The horizon of the lenticular lava flow which crops out on the southern coastal cliff at Yatsuiso is O2 of the Older Oshima Group. 2. The scoria cone Sado-yama, is inferred to have been formed in the O10 time. 3. The horizon of the uppermost one of three lava flows which crops out on the coastal cliff from Kootoshi to Otaine is O14. 4. The explosions which occurred to the southeast of Oyanokubo in the O15 time was followed by the ground-surge. 5. In the O8 time, steam explosions occurred at the Kakiharaiso coast and a large quantity of accretionary lapilli with scoria cores was formed, the explosions were followed by another ground-surge.
