Is Fuji about to blow its top?


Could the March 2011 earthquake be a harbinger of another disaster – an eruption of Mount Fuji? Some believe so.

Fuji-san - majestic - and dangerous?

Majestic Mount Fuji is an icon of Japan, and is frequently pictured along with cherry blossom as a Japanese symbol of peace and tranquillity. It is sometimes hard to remember that it is an active volcano, whose last eruption occurred a blink of an eye ago – in geological terms (1707). Indeed, in recorded history, since 781, there have been sixteen eruptions (of which twelve took place between 1083 and 1511).

Some geologists believe that major earthquakes, such as the one that occurred on March 11, 2011, are the precursor of Fuji’s eruptions. The head of Japan’s volcanic eruption prediction panel, Professor Toshitsugu Fujii, claimed last October that the magma chamber beneath the mountain was under increased pressure, and this could lead to an eruption in the foreseeable future, stating that a silent period of 300 years was abnormal, and that the next eruption could be a large one. However, heightened pressure in the magma chamber is not the only factor that can trigger an eruption.

More recently, another academic specializing in the field, retired professor Masaki Kimura of Ryukyu University, has warned of an imminent eruption, which in his opinion will occur before 2015, and points to cracks and rising magma levels, as well as a rise in the water level of Lake Sai, to the north-east of the mountain as precursors of such an event. He has already authored one book and co-authored another expounding his views.

If, however, these prophets of doom are proved correct, and a major earthquake occurs, it will be expensive. In 2004, the Japanese government estimated that an eruption of Fuji-san could cause up to some $32 billion worth of damage from mudslides and ash (by comparison, the bill for the 2011 Tohoku earthquake could reach $35 billion).

Indeed in 1707, ash covered Tokyo (then known as Edo) to a depth of at least an inch. As the world learned from the Icelandic volcano Eyjafjallajökull in 2010, ash is a serious disruptor of air travel. With the wind in the wrong direction, both of Tokyo’s airports could be placed out of action, and it has also been pointed out that ash and dust could cause chaos in the IT sector, as the air-conditioning in data centers and so on would be affected. It is also worth remembering that in several places near the mountain, the expressways, rail tracks (including shinkansen bullet trains) and main road connecting Tokyo with the industrial hubs of Nagoya and Osaka all run close together – meaning that traffic between these areas would almost certainly have to take the “back road” through the mountains.

But there is no certainty that this will happen. Though the magma pressure is indeed high, it should be noted that earthquakes and volcanic activity are difficult to predict with any accuracy, and though the conditions described are present, this is not necessarily an indication that such an eruption will occur soon, and almost certainly there will be warning signs before any such event.

As Professor Shuji Yoshida of the Department of Earth Sciences at Chiba University points out, “It’s difficult to make long-term predictions about volcanos,” adding that shorter-term predictions within days to months prior to an eruption are possible, given clues such as swelling of the mountain and more thermal and seismic activities around the volcanoes. Although Fuji-san is becoming more active, he says, there will be ample warning if the worst does come to the worst.

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