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Myojin Knoll
"A large submarine caldera, Myojin Knoll, lies between Aoga-shima and Bayonnaise Rocks volcanoes in the Izu-Bonin arc. The 6-7 km wide caldera, one of nine along this arc, has walls 500-900 m high. The high point on the western caldera rim is a pumice-mantled remnant of the pre-collapse volcanic complex that reaches a depth of 360 m. The walls of the caldera, also known as Kita-Bayonnaise (North Bayonnaise) reveal rhyolitic lava flows, shallow intrusions, and volcaniclastic deposits. A voluminous blanket of coarse rhyolitic pumice from the caldera-forming eruption mantles the caldera rim and its outer flanks. Post-caldera eruptions formed a lava dome that rises 250 m above the caldera floor. The age of the caldera is not known, but was considered by Fiske et al. (2001) to perhaps be as young as a few thousand years. An active hydrothermal vent field lies on the eastern caldera floor and has produced a polymetallic sulfide deposit from vent chimneys up to 30 m high that emit fluids as hot as 278 degrees C."  -Smithsonian Volcano Archive
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