Twenty volcanoes are currently being monitored on a 24-hour basis by four regional observation centers operated by the Meteorological Agency of Japan. They include 13 volcanoes designated as Rank A because they are most active and seven that are less active but could cause serious damage because of their proximity to residential areas. Earthquake recorders, cameras, tiltmeters and GPS are installed around these volcanoes.
Data gathered through such equipment are analyzed at the centers, located in Sapporo, Sendai, Tokyo and Fukuoka. Yamasato said that based on the analyses, the centers issue three levels of warnings: volcanic alert, volcanic advisory or volcanic observation report. Governments in the vicinity of volcanoes take into account the centers’ judgment when deciding whether to issue evacuation orders, he said.
A recent series of eruptions at Mount Asama that began last month is the latest reminder that Japan is a country of volcanoes. Japan has 108 active volcanoes that have erupted at least once in the last 10,000 years. While the Meteorological Agency has succeeded in forecasting eruptions — in some cases by monitoring such pre-eruption signs as earthquakes — it is often hard to determine the timing, scale and duration of an eruption because each volcano is different. Also, many of the volcanoes do not have a fixed pattern of activity, making forecasts difficult, experts say.