This is a remarkable volcanic landscape, a crater lake and active volcano within a crater within another crater. To fully appreciate its complexity, the view in Google Earth is informative.
The inner crater is 7.5 km across. The outer crater is 12 km across and its walls rise 500 to 1,000 m high above the crater lake, the latter being 1,035 m above sea level.
The volcano rises 650 m above the crater lake. It has erupted a number of times over the last 200 years, on one occasion burying a village with great loss of life.