The Kikai-Akahoya eruption, which devastated parts of prehistoric Japan approximately 7,300 years ago, produced sharply contrasting demographic outcomes rather than uniform societal collapse. Occurring beneath the sea about 30 kilometres south of Kyushu, the eruption generated powerful earthquakes and tsunamis and deposited metres of ash across the landscape. Japan’s Jomon hunter-gatherer communities suffered substantial loss of life, while damaged ecosystems forced survivors to confront radically altered living conditions.
An international team led by Lund University analysed 540 radiocarbon dates from archaeological sites and used statistical models to reconstruct population trends. Published in Science Advances, the research found that southern Kyushu’s population had already been declining before the catastrophe, which intensified that trend. Northern coastal populations, however, continued expanding despite extensive environmental damage. Migration from more severely affected regions may partly explain this growth. Evidence also suggests that inland survivors moved towards the northern coast, where marine ecosystems recovered comparatively quickly, offering food resources that communities could exploit in new ways.
The demographic consequences extended beyond the immediate disaster zone: some previously expanding populations farther away, including communities along Japan’s Pacific coast, stagnated or declined. Possible contributing factors include temporary climatic disruption, damage to food resources and adverse health effects. Severe tooth wear in deer and wild boar, important prey for Jomon hunters, may have resulted from grazing on ash-covered ground. Overall, the findings challenge interpretations centred on either wholesale destruction or largely unaffected survival, highlighting instead a complex combination of regional losses, migration, adaptation and continued growth.
