The Meteorological Agency managed to issue a warning to municipalities about 13 hours before the eruption early Monday of Mount Asama, boasting its first successful alert since it started up the system in December 2007.
The agency alerted the municipalities of Miyota, Karuizawa and Komoro, all in Nagano Prefecture, and Tsumagoi, Gunma Prefecture, at 1 p.m. Sunday that the volcano warning level had been upgraded to 3 from 2, according to agency volcano department official Sadayuki Kitagawa.
All four municipalities responded promptly, Kitagawa said.
The warning was “the first success of this system,” he said.
A level 3 warning bars access to Mount Asama, whereas a level 2 would bar people from getting near the volcanic crater.
A Karuizawa official said the town closed some toll road sections after receiving the agency alert.
The agency heightened the warning level after observing signs of an eruption, including ground movements and an increase in the number of earthquakes with a high frequency of seismic waves, Kitagawa said.
Before a medium-size eruption in 2004, a sensor on the mountain captured similar signs, but the agency at that time was unable to predict the event or issue a warning because of a lack of accumulated data, according to a news report.
Last August, the agency raised the level to 2 from 1 for Mount Asama because of an increase in volcanic tremors and smoke discharge.
The agency system has warnings up to level 5. Level 1 means no risk, level 4 means prepare for an evacuation and level 5 means get away from the volcano.
Mount Asama last erupted in August. This was preceded by larger-scale outbursts between September and December 2004, the agency said.
Separately, the agency upgraded the warning level to 3 from 2 on Sakurajima in Kagoshima Prefecture after the volcano continuously erupted Sunday and Monday.