When Mount Moto-Shirane in Gunma Prefecture erupted without warning Jan. 23, killing one person and injuring 11 others, the Meteorological Agency was unable to issue an alert immediately after the eruption — the first one was issued only about an hour later. The town of Kusatsu, the site of a ski resort near the volcano, only managed to broadcast a disaster warning through a wireless system 50 minutes after the eruption. Along with verifying what happened at the volcano, the agency needs to look into whether the volcano observation and alert system in the area worked. The government and the volcanologist community should re-examine the current monitoring and alert system, and review ways to best respond to eruptions once they have taken place.
Japan has 111 active volcanos — accounting for about 7 percent of active volcanos the world over — and 50 of them are observed round the clock under the Meteorological Agency’s volcano monitoring program. The volcanic area where the eruption occurred last week is one of these 50 areas. The Tokyo Institute of Technology has an observatory there, making what happened all the more shocking.
The eruption took place at the Kagamiike crater on Mount Moto-Shirane. Volcanologists and the agency had not anticipated an eruption at that site since there had been no volcanic activity there in some 3,000 years. The monitoring efforts in the area are concentrated at the Yugama crater of Mount Shirane, some 2 km to the north. Data submitted to the Coordinating Committee for the Prediction of Volcanic Eruption indicate the Jan. 23 eruption was very sudden. Volcanic tremors were observed in the area around 9:59 a.m. and the eruption took place at 10:02 a.m.
It is clear that the system to observe Mount Moto-Shirane is inadequate, although even a better one may not have enabled the prediction of a phreatic eruption — one that is steam-driven — which likely took place Jan. 23. This eruption should prompt the agency to look into whether the nation’s network of seismometers and video cameras to monitor volcanic activities has too many holes. While there are budgetary constraints, the agency should make the best use of its resources to increase efficiency of the observation network. The hazard map for volcanic activities and eruptions did not cover the site where last week’s eruption took place. The agency should review the way the map is created based on the understanding that volcanic activities can be very irregular.
The agency needs to analyze data from the latest eruption to determine the exact extent of the damage — including identifying the areas where the volcano spewed stones and ash, the specific type and scale of the eruption, whether hot water was discharged and whether there were debris flows.
It should also scrutinize how and why it took so long to issue an eruption alert. The first warning came about an hour after the eruption, raising the volcanic status level from 1 to 2 on a scale of 5 — a level at which entry into the crater area is restricted. About one hour and 50 minutes after the eruption, it raised the status level to 3, under which entering the mountain area is either banned or restricted. However, the agency did not share this warning with the Kusatsu Municipal Government.
The system of issuing a prompt eruption alert was established in the wake of the 2014 eruption of Mount Ontake on the Nagano-Gifu border, which killed 58 people, in an effort to encourage people to evacuate and limit casualties as much as possible. Explaining why the warnings were not issued immediately, the agency said it took time to confirm the facts related to the eruption due to the lack of monitoring cameras near the site. In such a case, the agency should get information from climbers and tourists who were near the scene as quickly as possible and issue relevant warnings — even if the information provided cannot be verified — under the principle that safety comes first. Municipalities near volcanos also should act under the same principle, although they may get conflicting information, as the Kusatsu town office did.
Many of the nation’s volcanos constitute tourism resources, and people may not have a sufficient sense of caution regarding the possibility of eruptions. Most municipalities near volcanos are said to lack advance evacuation plans in the event of an incident.
Although what happened last week at Mount Moto-Shirane reminds us of the difficulty of forecasting volcanic eruptions, that should not lead the government to slacken its efforts to improve the system to monitor volcanic activities. A good starting point would be to allocate sufficient resources to train a new generation of volcanologists since the nation is suffering from an acute shortage of young experts in the field.