Because of volcanic activity and nature conservation, landing on the island requires the approval of the Agency for Cultural Affairs.

Mount Kanpo (寛保岳, Kanpo-dake) had a major eruption on 27 August 1741, which created a large horseshoe-shaped caldera breached to the north and extending from the summit down to the seafloor at the base of the volcano.

This event produced a mostly-submarine debris avalanche that traveled 16 km and triggered a large tsunami, which devastated the coasts of Hokkaido, western Honshu, and Korea, causing nearly 1500 deaths.

The 1741 eruption was the largest in historical times at Ōshima and ended with the construction of a basaltic cinder cone at the head of the breached caldera.

Ōshima is the northern limit of the breeding grounds for the streaked shearwater and is part of the Matsumae-Yakoshi Prefectural Natural Park.