Boomerang Seamount, an active submarine volcano 18 km NE of Amsterdam Island, was first discovered during a bathymetric survey in 1996. It rises to within 650 m of the ocean surface and has a 2-km-wide summit caldera that is 200 m deep. Rift zones that extend to the SE and N give it an arcuate shape. A basaltic volcano, it lies along the axis of the Southeast Indian Ridge and marks the site of the Amsterdam-St. Paul hotspot. This hotspot may have been the source of the Ninetyeast Ridge submarine volcanoes on the Australian Plate prior to its "capture" by the Southeast Indian Ridge, after which volcanism was restricted to the Antarctic Plate. Very short half-life radionuclide dating of fresh volcanic glass samples recovered during the 1996 expedition indicated that it had erupted only about 5 months earlier (Johnson et al., 2000). Water column temperature anomalies above the seamount suggest the presence of hydrothermal activity within the caldera.