Perils lurking in pleasure

楽しさにひそむ危険 ―御嶽山の噴火から学ぶこと―


Mount Ontake that straddles Nagano and Gifu prefectures erupted on Sep­tember 27 after a hiatus of seven years. The country’s worst postwar volcanic mishap left 57 people dead and six others missing. Search efforts by Self-Defense Forces and police rescuers for those listed as missing were called on October 17 for the remainder of the year because the snowfall near the top of the mountain could cause a secondary disaster. They decided to wait until the snow melts and the climbing regulation is lifted.



The 3,067-meter-high Mount Ontake is one of Japan’s highest and is listed as one its 100 celebrated peaks. Despite its height, it is popular among families as it is not difficult to climb. It also attracts many tourists. In fact, 70 percent of the residents of Otaki Village at the foot of the mountain are engaged in the tourist business.



The latest eruption was said to be a vapor explosion, which occurs when groundwater is heated and rapidly expanded by subterranean magma. The volume of erupted ashes and rocks was estimated at 500,000 to 1.1 million tons, or as much as that in the previous major eruption in 1974. They fell onto wide areas. Cinders flew northward over a distance of 1.3 km from the crater, with some rocks 50~60 cm in diameter blown out at a speed of 350~400 km/h. Their impact was said to be as powerful as the one caused when a small truck collided head-on against a wall.


etting that aside, why did the eruption cause such heavy casualties? The 1974 explosion caused no human damage although it was about the same in scale as the latest one. Some people pointed out that a number of climbers were near the top of the mountain, the best spot to view autumn leaves, and that many of them were taking rest there as it was lunch time when the eruption occurred. However, pundits cited two more crucial factors.



One was the lack of information made available to the climbers. According to the Meteorological Agency, more than 100 volcanic temblors had been observed 11 days before the eruption and that had been made known to the local municipalities. But because no swell of mountain slopes nor magma ascent had been observed, the agency kept the eruption alert at one (normal) on the scale of five. As the tremors turned less frequent later on, the municipalities kept a watchful eye but stopped short of taking new precautions such as a warning to climbers.



The other was the behavior on the part of climbers. People are required to submit their plan before they start climbing the mountain. But as it is only on a voluntary basis, many climbers apparently did not register their plan on that day. The difficulties in confirming the number of climbers and their identities made the subsequent search efforts harder. These factors together obviously led up to the tragedy. By making the registration mandatory, getting the number of people involved would be easier when something happened.


 The eruption of Mount Ontake has changed the Japanese people’s consciousness of volcanos. One American exchange student at Chuo University said that the anti-disaster consciousness is high in his country because it had big volcanic eruptions in the past and eruptions are quite frequent in Hawaii. Many Americans know how seriously their community can be damaged and what they should do in case of a volcanic eruption, he said.



Now that we have renewed our awareness of the danger of volcanoes, we should deepen our anti-disaster consciousness and take greater precautions without simply seeing an eruption as a natural phenomenon.



(Written by: Natsumi Nakano)