Abstract
Izu-Oshima volcano consists mostly of subaerially deposited volcanic products. On the sea cliff, however, the water-laid deposits are intercalated in the O42 (about 7, 500 yB.P.) and O1 (about 1, 500 yB.P.) members of the Older Oshima Group. Layers of coastal gravels are observed in the Y5-Y1 (A.D. 1338-the present) members of the Younger Oshima Group near the present coast. These layers show imbricate structure indicating landward flow. They are interpreted as wind-transported from nearby coastal beach. These nearshore deposits were presumably resulted from the variation of the sea level in height. In the O1 age, lagoons were formed along the coast. In the S2 age (about A.D. 550), remarkable emergence of the shoreline occurred. After that, the island has kept subsiding gradually.
