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.