7,300-year-old supervolcanic blast caused local population collapse in Japan

Around 7,300 years ago, one of Earth’s largest volcanic eruptions devastated prehistoric Japan, triggering severe population declines in certain regions while communities elsewhere continued to grow, according to new research.

“This eruption must have been devastating,” said Peter Jordan, senior author and professor of archaeology at Lund University.

Exploding from the seabed with little warning, “it battered the Japanese islands with powerful earthquakes and enormous tsunamis, and then blanketed the landscape with meters of volcanic ash,” he added.

Lund University researchers found that the Kikai-Akahoya eruption produced markedly different demographic outcomes across Japan, challenging longstanding theories that the catastrophe had either wiped out entire communities or left them largely untouched.

Until this latest study in Science Advances, two theories dominated academia: the eruption devastated southern Japan, causing widespread societal collapse, and some communities survived the catastrophe and maintained their traditions. Neither turned out to be true.

Ancient communities faced different outcomes

The eruption at the Kikai caldera occurred about 30 kilometers south of Kyushu, when Jomon hunter-gatherer communities inhabited Japan.

The eruption registered a Volcanic Explosivity Index (VEI) of 7 and released an estimated 332 to 457 cubic kilometers of volcanic material. A Volcanic Explosivity Index (VEI) of 7 is classified as a super-colossal eruption.

After analyzing 540 radiocarbon dates from archaeological sites across Japan, researchers used statistical models to reconstruct population trends before and after the catastrophe.

Southern and central Kyushu experienced severe population declines. However, southern Kyushu’s population was already decreasing before the eruption, suggesting the disaster accelerated an existing trend.

By contrast, populations along its northern coast continued growing despite the widespread environmental destruction. Researchers suggested that survivors from the south may have relocated northward, where coastal ecosystems recovered more quickly.

“The disaster caused major loss of life. However, survivors migrated, forged new social relations, innovated new kinds of economy, and appear to have found creative ways to exist and later thrive in the new post-disaster conditions,” said lead author Enrico Crema, a professor at Cambridge University.

Population declines extended beyond the eruption zone

The explosion also affected demographic regions farther from the volcano. Some communities stagnated or declined afterward, including areas along Japan’s Pacific coast.

Researchers presented several hypotheses: damage to food resources from volcanic ash, climate change, and adverse health effects on humans and animals. However, the researchers acknowledged that the available evidence could not conclusively establish which environmental factors caused the population changes.

Even so, the findings challenged traditional interpretations of the eruption as an event that permanently devastated prehistoric Japan through widespread societal collapse.

Instead, the researchers found traces of regional population losses, continued growth, and possible migration between affected communities. Society did not collapse after the volcanic explosion, although the region was heavily affected.

The study provided researchers with “a deeper understanding of the contingent ways in which cultures and societies cope with sudden shocks and catastrophes,” said Jordan.

“Even in the most impossible situations, survivors and communities have choices, however limited: they need to act and make decisions; they need to adjust, collaborate, and find new connections and social networks,” Jordan concluded.