The small 2.5 x 3.5 km dominantly basaltic island of Aogashima is surrounded by steep cliffs and contains a small 1.7 x 1.5-km-wide caldera. Two pyroclastic cones were formed inside the caldera during the latest eruption from 1780 to 1785. Growth of the volcano began with construction of the Kurosaki stratovolcano in the NW part of the island, after which the main stratovolcano began growing in the SE. Both summit and flank vents produced pyroclastic surges and lava flows. Late in the construction of the main cone a 1-1.5 km crater was formed on the SE flank. About 3000 years ago pyroclastic surges swept over the entire island. During about the next 600 years, lava flows and scoria deposits filled the SE crater, which also collapsed repeatedly. The current Ikenosawa crater was considered by Takada et al. (1992) to have formed by ring collapse at the time of a debris avalanche, after which the volcano was quiescent until the eruptions of historical time.