Izu Islands (Japan)
Suiyo Seamount, one of the Shichiyo Seamounts, named for the 7 days of the week, lies south of Sofugan volcano. Suiyo Wednesday is an basaltic to dacitic submarine caldera and lava dome that rises abaout 1400 m from the sea floor to within 1418 m of the sea surface. The summit caldera is 1.5 km wide and about 500 m deep. Major hydrothermal activity was observed in July 1991, with temperatures reaching more the 290 degrees Centigrade, and the volcano was reclassified as active by the Japan Meteorological Agency.