|Native name: 大島, Ōshima|
|Area||9.73 km2 (3.76 sq mi)|
|Width||4 km (2.5 mi)|
|Highest elevation||732.4 m (2,402.9 ft)|
|Highest point||Mount Era|
Ōshima (大島?) is an uninhabited island in the Sea of Japan, 50 kilometres (31 mi) to the west from Matsumae town and therefore the westernmost point in Hokkaidō. It is part of the town of Matsumae in Matsumae District, Oshima Subprefecture in Hokkaidō, Japan. To distinguish Ōshima from other islands with the same name, it is sometimes known as Oshima Ōshima (渡島大島?) or Matsumae Ōshima (松前大島?).
At 9.73 square kilometres (3.76 sq mi), Ōshima is the largest uninhabited island under Japanese sovereignty. The island is a double caldera with a scoria hill rising in the middle. It is the peak of two overlapping stratovolcanoes and their associated calderas, Mount Higashi and Mount Nishi. The highest peak, Mount Era (江良岳 Era-dake?) at 737 metres (2,418 ft), is part of a triple volcano. The peak rises close to 2,000 metres (6,600 ft) from the sea floor. The island consists of mafic alkali and non-alkali volcanic rock, less than 18,000 years old.
Because of volcanic activity and nature conservation, landing on the island requires the approval of the Agency for Cultural Affairs.
Because of the island's isolation and volcanic activity there are almost no records of its past left behind. Mount Kanpo (寛保岳 Kanpo-dake?) had a major eruption on 27 August 1741. The next day a tsunami struck the opposite shore and killed 1,467 people from Kumaishi to Matsumae.
Flora and fauna
Ōshima is the northern limit of the breeding grounds for the streaked shearwater and is part of the Matsumae-Yakoshi Prefectural Natural Park.
- "Oshima-Oshima". Global Volcanism Program. Smithsonian National Museum of Natural History. Retrieved 2008-12-13.
- "OSHIMA O-SHIMA". Quaternary Volcanoes in Japan. Geological Survey of Japan, AIST. 2006. Retrieved 2008-12-13.
- "Hokkaido". Seamless Digital Geological Map of Japan. Geological Survey of Japan, AIST. Nov 2, 2007. Retrieved 2008-12-13.
- Based on the translation of ja:渡島大島 on 12 December 2008