Aso Caldera

Aso caldera (also known as Asosan, the Aso Volcano or Mount Aso, although the later term usually is used related to its currently active vents) is a geographical feature of Kumamoto Prefecture, Japan. It stretches 25 kilometers north to south and 18 kilometers east to west. The central core "Aso Gogaku" is the five major mountains in the area. Aso valley (Asodani) runs along the northern base of Mount Aso and Nango valley (Nangodani) along the south. According to research of caldera sediment, lakes used to exist in these valleys. The dried-up lake areas have come to be called Old Aso Lake, Kugino Lake, and Aso Valley Lake. The Kikuchi, Shirakawa and Kurokawa rivers now drain the caldera.