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​How Volcanic Eruptions Threaten Nuclear Power Plants

There are 110 volcanoes in nuclear heavy Japan. Is that safe?
Japan’s Mount Aso volcano erupts. Image: Screenshot from Japan Meteorology Agency YouTube video

On Monday, Mount Aso, a volcano found on Japan's main southern island of Kyushu erupted, spewing out a plume of grey smoke 2 kilmometers (1.2 miles) high. So far, no casualties or serious damages have been reported, and the 30 tourists who happened to be hiking there at the time have been whisked out of harm's way.

The region is also home to a nuclear power station, which was only recently restarted, amidst a considerable amount of public outcry, in August 2015. It gives rise to the question, as Japan rethinks its relationship to nuclear power in the wake of the Fukushima crisis: how logical is it to have a power station in the vicinity of a bunch of active volcanoes?

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Monday's eruption—classed as a Level 3—wasn't humungus. Yet there are two risks that can't be ignored: Firstly, ash from eruptions can affect nuclear power plants; and secondly, mammoth eruptions that could threaten a reactor directly—however small the probability—cannot be ruled out.

Japan lies in what's know as a "Ring of Fire." It's a 40,000 km (25,000 mile) horseshoe-shaped basin consisting of a super-mix of fault lines, oceanic trenches, volcanic belts, and volcanic arcs. Of the roughly, 1,500 active volcanoes in the world, around 110 of them are here. In Japan, there will always be a risk wherever you plonk a nuclear power plant.

"The Sendai nuclear plant is sufficiently distant from the Sakurajima and Kirishimayama volcanoes to be safe from the direct impact of destructive phenomena such as lava flows or pyroclastic flows, but could be affected by ash fall during a sufficiently large eruption, and provided the wind is blowing in its direction," Bill McGuire, a leading British volcanologist and Emeritus Professor of Geophysical & Climate Hazards at University London, told me in an email.

McGuire says that Mount Aso is characterised by "frequent, relatively small, eruptions, and no significant explosion has been recorded in the last 10,000 years or so," like today's. The eruption may have been on the small side, but that doesn't necessarily mean that it won't be detrimental to the nuclear power plant in the area. McGuire explained that nuclear power plants in the southern island of Kyushu wouldn't be at risk from molten flowing lava, due to the distance. However, he said that ash, could still pose a problem.

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Time-lapse of Mount #Aso, #Japan's largest active volcano, erupting this morning. (via @kumamoto_rkk) pic.twitter.com/nMeHBQvBTN
— Alejandro Alvarez (@aletweetsnews) September 14, 2015

"Ash is a rather unspectacular hazard, but can cause major problems through clogging filters and machinery and infiltrating sensitive electrical and electronic systems."

Still, while 10,000 years might seem pretty epic when viewed along a human timescale—according to Charles B. Connor, a volcanologist at the University of South Florida, you definitely need to think about that time frame when you're building a powerful nuclear reactor.

"Volcanologists don't know much about the time scales or precursory activity to large eruptions as we don't get a chance to observe them so often," Connor, told me over the phone. "That's an issue—we treat their eruptions probabilistically."

McGuire and Connor explained that there are several examples of nuclear power plants worldwide, built according to calculations based on the probability or large-scale volcanic eruptions happening or not. "Often, even though the natural hazard is clear, the facility is still built. Short-termism and the profit motive remain powerful drivers," McGuire told me.

Connor cites the Trojan Nuclear Power Plant in the northwest US state of Oregon (subject to Mount Saint Helen's eruption in the 1980s), and the Bataan Nuclear Power Plant in the Philippines as examples. While the Trojan Nuclear Power Plant remained unaffected by Mount Saint Helen's blast, Bataan was shut down in the 1980s by the Philippine government due to the volcanic risks in the region.

A spokesperson for the Kyushu Electric Power Co., Torahiko Komatsu, says that today's blast isn't a cause for concern, saying that the Sendai nuclear power station in question lies "145 km away" from Mount Aso. But there are still risks.

"Like Fukushima, there is a very low probability of a disastrous event [in Kyushu]," said Connor. "But even though a chance of eruption is small in the time of human experience, it's large in terms of huge facilities. That's why the difficulties arise and it becomes a tough societal decision for the government."

And that may be why, since Fukushima, Japan has struggled to decide where its future with nuclear power lies.