Even most Japanese people don't know that Kagoshima Bay in southern Japan is home to a gigantic active undersea volcano. 30,000 years ago this volcano, then on land, underwent one of largest eruptions ever in Japan, blasting ash across the Japanese islands. The eruption resulted in the Aira Caldera, a formation 20 kilometers across that currently sits 200 meters below the water's surface. A recent survey of the caldera discovered it contains a unique oceanic ecosystem that exists in only two other places in the world. In 2011, another major discovery was made: deposits of rare metals. Join us as we probe the mysteries of this enormous but little-known volcano.