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Snow-capped, symmetrically cone-shaped and awe-inspiringly tall, Mount Fuji has for centuries provided Japanese with something of a spiritual backbone, attracting hundreds of thousands of climbers every year.

But often overshadowed by its beauty is the fact that the mountain straddling Shizuoka and Yamanashi prefectures is an active volcano with a history of frequent blasts — hence its nickname as the “department store” of eruptions.

Experts say the precise timing of the next big one is unpredictable, but one Japanese volcanologist paints an urgent picture of the situation.

“Mount Fuji is on standby for the next eruption,” said Hiroki Kamata, a professor of volcanology at Kyoto University.

More than 300 years, he pointed out, have elapsed since the last eruption in 1707, an eerily long silence that surpasses the previous interval of around 200 years.

“It was long gearing up for another blast, but shaken by the Great East Japan Earthquake (that struck the Tohoku region in 2011), it is more unstable than ever. If that doesn’t make the eruption imminent, I don’t know what will.”

The 1707 blast is known as the Hoei Eruption, named after the Japanese era at the time. It spewed a massive amount of volcanic ash that annals show wafted all the way to today’s Tokyo.

Should the mountain erupt again, cinders could rain down on parts of nearby cities such as Gotemba in Shizuoka, with potentially life-threatening results, according to a council of central and local government officials tasked with hammering out safety measures in the event of an eruption. An economic loss of up to ¥2.5 trillion is expected, the council says.

It is the arrival of volcanic ash, however, that experts say could paralyze Tokyo and its surrounding metropolitan areas.

Ash is forecast to drift to the east due to the westerlies blowing over the archipelago and travel past Tokyo all the way to Chiba, according to simulated data published by a government task force in March last year.

That would wreak havoc on high-tech Tokyo, possibly causing blackouts, water shortages and malfunctions of electronic appliances as well as disrupting telecommunications, according to the task force. Trains might be suspended, too.

Airport terminals will be forced to shut down, it said, if runway markings are covered with ash. Health problems might also arise, with the inhalation of ash likely to cause a “strong sense of discomfort.”

Given the 1707 Hoei Eruption was likely triggered by a magnitude 8.6 earthquake that struck south-central Japan 49 days earlier, Kamata believes there is a high likelihood that a magnitude 9 Nankai Trough earthquake — should it happen in the near future as forecast by the government — would do the same.

But Takayoshi Iwata, director of the Center for Integrated Research and Education of Natural Hazards at Shizuoka University, offered a more nuanced view.

“It’s true that history has shown eruptions can be caused by earthquakes, but there were also times Mount Fuji erupted of its own accord, so it’s not necessarily the case there is a correlation with quakes,” he said.

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