Kikai Caldera

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Kikai Caldera is a massive underwater caldera up to 19 kilometres in diameter in the Osumi Islands of Kagoshima prefecture, Japan. It is the remains of the ancient eruption of a gigantic volcano.

Kikai Caldera was the source of one of the largest eruptions during the Holocene (10,000 years ago to present). About 6,300 years ago, pyroclastic flows from that eruption reached the coast of southern Kyūshū up to 100 km away, and ash fell as far as Hokkaidō. It had a VEI (Volcanic Explosivity Index) rating of 7.

Kikai is still an active volcano. Minor eruptions occur frequently on Iwo-dake, one of the post-caldera subaerial volcanic peaks on Tokara-Iwo-Jima. Tokara-Iwo-Jima is one of three volcanic islands, two of which lie on the caldera rim. The most recent eruptions have occurred in 2005.