They gave the public warning of danger to approach the crater area. JMA observed no volcanic tremors at this volcano these months, except for 5 volcanic earthquakes in August. The attention board for volcanic gas that was made just after the accident. This mud volcano has been observed since the 1997-spring. Hot water gushed out from some points, and yellowish silty deposits were found on the bottoms of small creeks.
Yellowish materials are sulfer sublimate.
The site of gas accident is the head of small V-shaped valley. The outlet of this valley locates just in the H2S gushing field. Turning point of the valley, where lake tarrace deposits acted as barrier against H2S gas. White flowers truned pink on the rock surface. The site of accident is on the bottom of valley.