The Kikai-Akahoya eruption, which devastated prehistoric Japan approximately 7,300 years ago, produced sharply contrasting demographic outcomes rather than uniform societal collapse. An international team led by Lund University reconstructed population trends using statistical models and 540 radiocarbon dates from archaeological sites across Japan. Published in Science Advances, the research examines how Jomon hunter-gatherer communities responded to a catastrophe that brought powerful earthquakes, enormous tsunamis, and extensive ash deposits. The volcano erupted beneath the sea about 30 kilometers south of Kyushu, releasing an estimated 332 to 457 cubic kilometers of volcanic material.
Southern and central Kyushu experienced severe population declines, although the downward trend in southern Kyushu had begun before the eruption. Northern Kyushu, by contrast, continued to experience population growth despite substantial, lasting environmental damage. Researchers suggest that migration from devastated southern areas may have contributed to this increase. Evidence also points to inland survivors relocating toward the northern coast, where marine ecosystems recovered relatively quickly. Access to these food resources, together with new ways of using them, may have supported further growth.
The demographic disruption extended into more distant regions, including parts of Japan’s Pacific coast, where earlier population growth stalled or reversed. Proposed explanations include temporary climate disruption, damage to food resources from ash, and adverse effects on human and animal health. Taken together, the findings challenge an all-or-nothing interpretation of the disaster: severe losses coexisted with continued growth, while survivors developed new social connections and ways of supporting themselves.
