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.

今年９月２７日、長野県と岐阜県の県境に位置する御嶽山が噴火した。御嶽山の噴火は７年ぶりのことだ。この噴火で５７人が死亡、６人が行方不明となり、火山事故として戦後最悪の惨事となった。自衛隊などによる行方不明者の捜索活動が続いた、山頂付近の積雪などで二次災害の危険性が高まり、１０月１７日で捜索活動は中断され、雪解けと入山規制解除を待つこととなった。

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.

御嶽山は、日本百名山に登録される日本有数の高さを誇る山である。標高３０６７メートルの高山だが、登山の難易度は低く、登りやすいということで、家族連れなどにも人気がある。そして観光客も多く、山の麓にある玉滝村では住民の７割が観光業に携わっている。

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.

今回の噴火は、地下水などが地下のマグマで温められ急激に膨張することによって起こる水蒸気爆発だった。灰や岩石などの噴出量は５０万～１１０万トンとされ、１９７４年に起きた大規模噴火時とほぼ同等の量で、広範囲に広がった。また、噴石は火口から北方向１・３キロまで飛び、中には直径５０～６０センチの岩石が時速３５０～４００キロで飛んだ。軽トラックにぶつけられるほどの衝撃だという。

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.

それにしても、今回の噴火でなぜこれほどまでの死者、不明者が出たのだろうか。７４年時の噴火も同じような規模だったにもかかわらず、人的被害はゼロだった。被害拡大の要因として、紅葉の見所とされる山頂付近に大勢の登山客がおり、しかも爆発が昼食時だったため休憩中の客も多かったことが挙げられているが、そのほか２点の要因が指摘されている。

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.

１つは、一般登山客への情報提供の不足。気象庁によると、噴火の１１日前まで火山性地震が１００回以上観測され、自治体側にも通知された。しかし、山の表面の膨張やマグマの上昇が観測されなかったことから警戒レベルを平常時と同じ「１」のままにし、その後地震回数が減ったことから、自治体は注視することにとどめ、登山客への警戒呼び掛けなど新たな対応を求めることはなかった。

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.

2つ目は、登山客の事前の行動だ。登山をする際には、登山届を出すことになっているが、それが任意であるため記入率はそれほど高くなく、登山客の人数や身元を把握することができず、噴火後の行方不明者の救助活動を遅らせてしまった。これが被害拡大につながったとされている。届提出を義務づけることで、なにかが起こったときの人数把握がスムーズに行えるのではないだろうか。

　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.

今回の噴火で、火山に対する意識が変わったように思われる。中央大学のある米国人留学生に話を聞いたが、数年前に自国でも大きな火山噴火が起こったことや、ハワイでは噴火が頻発していることもあり、防災意識は高い。もし噴火が起こった場合、自分が住む地域がどの程度の被害を受けるのか、噴火が起こったらどうすべきか、火山国では防災意識は当たり前のように備わっているようだ。

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.

日本でも、自然現象だからどうしようもないとあきらめるのではなく、火山の恐怖をみんなが再認識した今、取り組んでいかなければならないことがあるのではないだろうか。

(Written by: Natsumi Nakano)