A major volcanic eruption in Japan threatening the safety of tens of thousands of people is possible within the next three decades, say experts who have used new techniques to identify a buildup of magma in one of the country’s most active volcanoes.

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In a study published on Tuesday in the Scientific Reports journal, a team that included experts from Bristol University and the Sakurajima Volcano Research Centre in Japan said the new techniques showed a “substantial growing magma reserve” inside Sakurajima, located just off the coast of Kagoshima city, in south-west Japan.

The team said the magma buildup could trigger a repeat of the volcano’s deadly eruption of 1914, which killed 58 people and caused widespread flooding in Kagoshima, home to more than 600,000 people.

Dr James Hickey, the lead author of the study, said the team had found a new way to map the natural “plumbing system” inside volcanoes that could improve authorities’ ability to predict eruptions and issue earlier evacuation guidance.



“What we have discovered is not just how the magma flows into the reservoir, but just how great the reservoir is becoming,” Hickey said. “We believe that this new approach could help to improve eruption forecasting and hazard assessment at volcanoes not just in this area, but worldwide.

“We know that being forewarned means we are forearmed and providing essential information for local authorities can potentially help save lives if an eruption was imminent.”

Sakurajima is about 30 miles from two nuclear reactors that were restarted last year, as Japan resumed its nuclear power programme after the March 2011 Fukushima meltdown.

In 2013 the 1,117-metre-high Sakurajima – a popular tourist attraction – spewed ash as far as Kagoshima and sent rocks flying into populated areas, causing damage but no major injuries. Dramatic footage taken in the early evening in February last year showed the volcano erupting in a fiery blast before sending lava flows down its slope. It last erupted in July, sending ash 5,000 metres into the sky.

There are scores of active volcanoes in Japan, which sits on the Pacific “ring of fire” where a large proportion of the world’s quakes and eruptions are recorded. Mount Fuji, Japan’s most famous volcano – and its highest peak – is active but has not erupted since 1707. In September 2014, a major eruption on Mount Ontake in central Japan killed 57 people.

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The British and Japanese research team focused their study on Aira caldera – a vast, submerged crater that stores magma and feeds it into nearby Sakurajima, causing almost daily eruptions.

They found that the caldera – a cauldron-like volcanic depression – was supplying Sakurajima with about 14m cubic metres of magma every year, enough to fill Wembley stadium in London three and a half times over.

The magma is entering the volcano at a faster rate than it can be released through small, frequent eruptions, leading the researchers to conclude that a much bigger eruption is possible within the next three decades.

“The 1914 eruption measured about 1.5 km cubed in volume – a massive event,” Hickey said. “From our data we think it would take around 130 years for the volcano to store the same amount of magma for another eruption of a similar size – meaning we are around 25 years away.”