A volcano in Japan that erupted approximately 7,300 years ago, burying most of the archipelago in thick ash, has been silently preparing to make a powerful comeback, it appears.

The Akahoya eruption – known as the strongest volcanic explosions – took place when the Kikai Caldera in Kyūshū, Japan, erupted, spewing about 150 cubic kilometers (36 cu mi) of volcanic material.

The blast was so powerful it caused the volcano’s magma chamber to collapse, leaving a 12-mile wide scar, which is mostly underwater.

Now, as per a study published on Friday, scientists have discovered a dome of lava that lurks beneath the caldera.

Its magma plumbing could provide volcanologists with an insight into the entire caldera system, that could help them predict future eruptions that might occur in the Japanese archipelago.

“The most serious problem that we are worrying about is not an eruption of this lava dome, but the occurrence of the next supereruption,” said Yoshiyuki Tatsumi a volcanologist at Kobe University in Japan and lead author of the study that appeared in the journal Scientific Reports, according to The New York Times.

Previous analysis conducted by Dr Tatsumi shows just a one percent possibility of a supereruption in the Japanese archipelago in the next century. But, in case it does happen, it could eject nearly 10 cubic miles of magma, covering almost all of the country and its 120 million people in nearly eight inches of thick ash.

As per The New York Times, Dr Tatsumi and his colleagues at the Kobe Ocean Bottom Exploration Center conducted three surveys of the caldera, during which they used remotely operated vehicles to observe the depression. On their trips, they investigated the caldera using seismic analysis as well as geological and electromagnetic tests. They found the lava dome using an acoustic survey.

The trapped build-up of lava that threatens to erupt is estimated to have a volume of about eight cubic miles, a diameter of about six miles and a height of almost 2,000 feet.

This underwater dome has an immense volume of lava, more than the Yellowstone caldera and the Long Valley caldera, which have also been brewing with activity.

This site has experienced at least three supereruptions – one 140,000 years ago, another 95,000 years ago, and then the Akahoya eruption.

Scientists are yet to ascertain the exact time when the dome began to form – immediately after the eruption or gradually during the following years.

However, they did find that the lava dome was made of similar magma to what is seen in volcanoes on nearby islands.

Dr. Tatsumi said another survey in March will gather high-resolution images of the underground magma system, The New York Times reported.

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