Kikai Caldera, massive caldera, c.12 mi (19 km) in diameter, Ryukyu Islands, Kagoshima Prefecture, Japan. Located c.30 mi (48 km) from the southern tip of the densely populated major island of Kyushu, the caldera is mostly underwater, with a few small associated volcanic islands. It was formed some 6,300 years ago when the Akahoya supereruption caused the magma chamber to collapse. There have been a number of eruptions since 1988, mainly on one of the islands, and a lava dome within the caldera is expanding and is now c.100 ft (30 m) beneath the surface.
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