One of Japan's most active volcanoes is due a major eruption in the next 30 years, scientists have warned. At present, Sakurajima volcano is accumulating huge magma reservoirs, which experts say could be a precursor to a large eruption – similar to the one that took place in 1914, where an explosive eruption killed 58 and caused widespread flooding in the city of Kagoshima.

The region around the volcano is now home to 600,000 people. A large eruption at Sakurajima has the potential to cause significant damage, so understanding the size and timing of a future eruption for hazard preparation is vital.

In a study published in Scientific Reports, researchers have now assessed the build-up of magma beneath Aira caldera and Sakurajima volcano, with findings showing magma is being supplied to the system faster than it is being erupted (Sakurajima has small, localised eruptions almost every day).

The team, led by scientists at the University of Bristol, found the ground around the volcano has been continually uplifting – as the magma reservoir expands below the surface, the ground swells up. GPS deformation measurements and 3D computer models then allowed them to create a reconstruction of the magma plumbing system under the volcano.

Their findings showed that 14 million cubic metres of magma is accumulating every year. That is enough to fill Wembley Stadium 3.5 times over.

Lead author James Hickey said: "What we have discovered is not just how the magma flows into the reservoir, but just how great the reservoir is becoming. The 1914 eruption measured about 1.5 kilometres cubed in volume – a massive event. 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."

Sakurajima Volcano
Sakurajima Volcano in Japan is due a major earthquake in the next 30 years, the study shows Sakurajima Volcano Research Centre

While predicting when a volcano will erupt is not possible, the team say their findings should help authorities plan for future disasters. "We believe that this new approach could help to improve eruption forecasting and hazard assessment at volcanoes not just in this area, but worldwide," Hickey said. "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."

Haruhisa Nakamichi, associate professor at the Disaster Prevention Research Institute, Kyoto University, and co-author, said: "It is already passed by 100 years since the 1914 eruption, less than 30 years is left until a next expected big eruption, Kagoshima city office has prepared new evacuation plans from Sakurajima, after experiences of evacuation of the crisis in August 2015."