Mount Aso, Japanese Aso-san, volcano, Kumamoto ken (prefecture), Kyushu, Japan, rising to an elevation of 5,223 feet (1,592 m). It has the largest active crater in the world, measuring 71 miles (114 km) in circumference, 17 miles (27 km) from north to south, and 10 miles (16 km) from east to west. Its caldera (bowl-shaped volcanic depression) marks the original crater and contains the active volcano of Naka-dake and numerous hot springs. The crater is inhabited and is crossed by roads and railways. Its mountain pastures are used for cattle raising and dairy farming. The volcano is the central feature of Aso-Kuju National Park.