The eruption Saturday of Mount Ontake, which straddles Nagano and Gifu prefectures, has reminded us that Japan is indeed a country with many volcanoes that could erupt unexpectedly.

It is imperative for central government organizations, especially the Meteorological Agency, and local authorities to learn lessons from the disaster at Mount Ontake in taking steps to limit casualties and damage in the future.

When the volcano erupted, the area near its 3,067-meter peak was crowded with some 300 climbers who had come to see the tinted autumnal leaves. Hot volcanic ash and cinders left at least 36 climbers confirmed or feared dead, and dozens more injured. Mount Ontake — long revered as a sacred volcano and a subject of mountain worship — had its first-ever eruption in recorded history in 1979 when it sent 200,000 tons of ash into the sky. That major eruption was followed by minor explosions in 1991 and 2007. Mount Ontake is now one of 47 volcanoes in Japan — of the 110 considered active — that are subject to around-the-clock monitoring.

The Meteorological Agency has been watching Mount Ontake by using a system to measure changes in its shape as well as a clinometer, seismograph and a camera with a telescope.

Since mid-September, minor volcanic quakes had been detected repeatedly beneath the peak— including 52 times on Sept. 10 and 85 times on Sept. 11. These were the first two times that more than 50 volcanic tremors a day had been reported at Mount Ontake since the monitoring of such quakes began shortly before its last eruption in March 2007.

Still, the agency was unable to predict Saturday’s eruption. It was not until 44 minutes after the eruption that it raised the level of caution from 1 (normal) to 3 (banning entry into the mountain area) — out of a scale of 5.

The Coordinating Committee for the Prediction of Volcanic Eruption said Sunday that the eruption was phreatic — an explosion of steam that occurs when magma heats ground water, causing instantaneous evaporation. In most cases, this type of eruption is not accompanied by geological deformations. It is, therefore, difficult to predict a phreatic eruption by observing changes in the mountain shape or by the readings on a clinometer. Geological data in fact had not indicated rising levels of magma. What happened on Mount Ontake strengthens the case for honing the capability to predict steam eruptions, which often shoot up ash and rocks.

As volcanic activity is expected to continue on Mount Ontake, it is important to take precautions against pyroclastic flows, further falls of ash or an avalanche of accumulated ash.

Although the Meteorological Agency was unable to predict Saturday’s explosion, it had issued “volcano observation information” three times from Sept. 11 through 16 to nearby local governments. The problem is that nobody cared about such information. In hindsight, the agency could have taken into account the increased number of climbers on the mountain this time of year, and provided the information not only to local authorities but also to mountain hut operators and the media. Mountain guides and tourist companies should be encouraged to check all sources of such information.

In Saturday’s eruption, mountain huts played an important role as shelters. Helmets kept there turned out to be useful for the evacuees. The central and local governments should promote the building of such shelters in volcanic mountains.

While about 7 percent of the world’s active volcanoes are concentrated in Japan, the number of volcanologists is dwindling in this country. Such experts are stationed only at Mount Sakurajima in Kagoshima Prefecture and a few other volcanoes. The national government should push a long-term project to train scientists who study and monitor volcanic activity.

In a time of both misinformation and too much information, quality journalism is more crucial than ever.
By subscribing, you can help us get the story right.