Aira Caldera, Supervolcano in Kagoshima Prefecture, Japan

Aira Caldera is a supervolcano in Kagoshima Prefecture, Japan, stretching roughly 23 kilometers across and forming a large depression in southern Kyushu Island. The depression sits partly beneath Kagoshima Bay, with the active Sakurajima volcano rising along its rim and emitting smoke columns regularly.

The caldera took its present shape in the Aira pyroclastic eruption about 30,000 years ago, when the Ito pyroclastic flow laid down the Shirasu plateau and Aira-Tn ash fell as far as the Kanto region. The Osumi pumice fall and the Tsumaya and Tarumizu flows preceded it. Sakurajima, the post-caldera volcano, was born about 26,000 years ago.

Kagoshima city lives with daily volcanic ash that settles on streets and rooftops, swept away regularly by residents. Public washing stations stand ready for people to clean clothing and vehicles when wind carries ash into settled areas.

The bay offers several viewpoints along the coast where visitors can survey the shape of the caldera and Sakurajima volcano. Clear days bring sharper views, especially in early morning before clouds or ash build up.

Beneath the bay a magma chamber slowly expands, lifting the seafloor in places by several centimeters each year. Researchers measure this movement and use the entire area as a geological laboratory to understand volcanic behavior.