Kasuga 2, also referred to as Minami Kasuga (South Kasuga), is the central of three volcanoes forming the Kasuga seamount chain, which trends SSW from the volcanic front of the Izu-Marianas arc. It rises from about 3,000 m depth to within 170 m of the ocean surface. Two subsidiary cones are located low on the E flank. The morphology is more complex than Kasuga 1 to the north, and prominent ridges separate slopes of interspersed volcaniclastic and lava flow fields. Radiometric dating indicates an age of less than 8,000 years and probably less than 1,000 years; radium/thorium disequilibrium ratios suggest the flows may be only a few centuries old (Fryer et al., 1997). Active hydrothermal vents are located at the summit, at the base of summit ridges, and on the lower flanks.