A massive volcanic eruption that struck Japan about 7,300 years ago had a devastating impact on prehistoric communities, but its aftermath was far more complicated than scientists once believed. While some populations declined or disappeared from affected areas, others continued to grow despite the destruction.
An international research team led by Lund University investigated how the Kikai-Akahoya eruption changed population patterns across Japan. Their findings challenge the idea that the disaster either completely wiped out nearby communities or left them largely unaffected. Instead, the researchers uncovered a surprising mix of population decline, migration, adaptation, and growth.
A Catastrophic Volcanic Eruption in Ancient Japan
When the Kikai-Akahoya volcano erupted beneath the sea approximately 7,300 years ago, Japan was home to Jomon communities that depended on hunting and gathering for survival.
“This eruption must have been devastating, exploding out of 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,” explains senior author Peter Jordan, professor in archaeology at Lund University.
For decades, archaeologists have disagreed about what happened to the people living near the eruption. One theory describes an almost complete apocalypse, with human populations abruptly disappearing from areas closest to the eruption. Another suggests that some communities managed to survive even relatively close to the disaster.
The new findings indicate that neither explanation fully captures what happened. The eruption severely damaged ecosystems, forced people from their homes, and made some regions uninhabitable. Yet evidence also points to remarkable adaptability among survivors, with certain populations actually increasing after the catastrophe.
“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,” says lead author Enrico Crema, professor at Cambridge University.
How the Volcanic Disaster Reshaped Japan’s Population
The researchers identified striking differences in how communities across Japan responded to the eruption.
In southern Kyushu, Jomon populations had already been shrinking long before the volcano erupted. By the time the disaster occurred, relatively few people remained in the region, which was primarily visited by highly mobile groups of foragers.
Northern Kyushu followed a very different pattern. Its population had been increasing before the eruption, and that growth continued through the catastrophe and afterward, even though the surrounding ecosystems experienced extensive and lasting damage. The researchers suggest that people fleeing the most severely affected regions may have contributed to this unexpected population growth.
Evidence also indicates that survivors who had lived inland relocated toward the northern coast. Marine ecosystems in these areas recovered relatively quickly, providing valuable food resources. By developing new ways to take advantage of the sea’s abundance, these communities may have supported further population growth.
Unexpected Effects Far From the Volcano
Perhaps even more surprising, the researchers identified population changes in parts of Japan much farther from the eruption.
These distant regions had experienced population growth before the catastrophe, but afterward, that growth stalled or even reversed. Such widespread demographic consequences had not previously been recognized.
Several possible explanations could account for these changes. The eruption may have caused temporary climate disruptions that affected communities across Japan. Another possibility involves severe tooth wear among deer and wild boar, two important food sources for the Jomon (possibly a consequence of the animals grazing in ash-covered landscapes). Other volcanic effects on human health and living conditions may also have contributed.
Together, these findings suggest that the consequences of a massive natural disaster can extend well beyond the areas experiencing the most immediate destruction.
According to Jordan, the results demonstrate that the effects of catastrophes are rarely straightforward. Even when faced with overwhelming destruction, human communities can respond in different ways, depending on their circumstances and the choices available to them.
“This study helps in creating a deeper understanding of the contingent ways in which cultures and societies cope with sudden shocks and catastrophes. 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,” he concludes.
