Asosan

Asosan, also written as Aso-san, is an active volcano located in Kumamoto Prefecture on the island of Kyushu, Japan. It forms the central feature of Aso Kuju National Park and is one of the largest volcanic complexes in the world by area.

The Aso caldera is a massive volcanic crater formed by several large eruptions during the late Pleistocene. It measures roughly 18 by 25 kilometers in diameter. Within the caldera lies a volcanic complex with multiple peaks, the best known of which is Nakadake, at about 1,592 meters, and historically the most active crater.

The interior of the caldera features several craters, fumaroles, hot springs, and crater lakes. Nakadake is the primary active crater, and the area experiences ongoing volcanic activity including ash emissions and gas releases. The volcano is closely monitored by the Japan Meteorological Agency, which issues warnings and restrictions as needed to protect nearby residents and visitors.

Access to the crater area is possible when conditions permit, with roads and, at times, a ropeway connected to viewpoints and crater sites. Tourism is centered on views of the caldera, hiking around the rim, and observing the volcanic landscape, though visitor access can be limited during periods of heightened activity.

Asosan is part of a broader volcanic and seismic region and remains a focus of ongoing geological study and hazard monitoring in Japan.