Fig. 2

Photographs of the degassing and eruptive activities at the Nakadake crater, Aso volcano. All photographs, except c, were taken from the location 4 in Fig. 1, and show the two separate degassing sources of the main vent (or the crater lake) on the left and the fumaroles on the southern rim on the right. a The crater lake and the fumarolic area during the quiet period on August 19, 2010. b Gas emission occurs at the main vent after disappearance of the crater lake and the fumaroles on November 18, 2014. c Intensive ash eruption on January 12, 2015. d The intermediate ash eruption on January 13, 2015. e The weak ash eruption on March 17, 2015. f Gas emission from the main vent on May 19, 2015