Aso volcano shows signs of instability since 2013, with small explosions of phreatic type.
During 2013, the acidic crater lake gradually decreased and disappeared in June, the result of a rise in temperature and changes in the hydrothermal system. This phenomenon has already been observed in 2011. (GVP)
JMA / Japan Meteorological Agency increased the alert level to 2 on August 30, 2014, and reported a small inflation in its latest bulletin ... in connection with the assumption of a magmatic intrusion. The exclusion zone of 1 km. around the volcano is effective.
Evolution of the acidic lake between January and June 2013 - Excite webtl Photo / via Culture Volcans.