The Japan Meteorological Agency has raised the eruption alert level for Mt. Hakone, which straddles the border between Kanagawa and Shizuoka prefectures, warning of a possible phreatic explosion.
The mountain’s alert warning was raised on Wednesday from Level 1, indicating a normal situation, to Level 2, which restricts access around the volcanic vent. It was the first Level 2 warning regarding the mountain since the five-level alert system was introduced in 2009.
On Tuesday, 116 volcanic earthquakes were observed, a record for one day. Three earthquakes that could be felt were confirmed, the first in four years.
Sadayuki Kitagawa, head of the agency’s volcanology division, said at a press conference Wednesday morning that the earthquake could have been caused by hot gas and other elements deep in the ground.
“This is obviously different from past situations. As hot water that has pooled in shallow areas has become unstable, there is a higher possibility of a phreatic explosion,” Kitagawa said in explanation of the raised alert level.
As of noon Thursday, 10 volcanic earthquakes had already been observed, and the agency continued calling for caution. Responding to the raised alert level, all services on the Hakone Ropeway were suspended between Sounzan and Togendai stations, which is inside the area covered by the evacuation directive. An about 1.2-kilometer prefectural road to a parking lot for Owakudani was closed to traffic.
Mt. Hakone’s last eruption is believed to have been sometime in the 12th or 13th century.
The town of Hakone has already prohibited entry to Owakudani and surrounding areas. The Hot Springs Research Institute of Kanagawa Prefecture explained that only the area surrounding Owakudani is expected to be affected at this stage. According to Prof. Setsuya Nakada, a volcanology expert at the University of Tokyo’s Earthquake Research Institute, “Even if [Mt. Hakone] does erupt, it will likely be on a smaller scale than that of last year’s eruption of Mt. Ontake.”