Kikai-akahoya eruption reshaped prehistoric japanese population patterns, study finds

The Kikai-Akahoya eruption originated beneath the seabed and produced powerful earthquakes, large tsunamis, and ash deposits several metres deep across the Japanese islands. At the time of the eruption, the Jomon people inhabited Japan, living as hunter-gatherer communities. Senior author Peter Jordan, professor in archaeology at Lund University, described the event as erupting "out of the sea bed with little warning," causing widespread and severe environmental disruption across the region.

The demographic consequences of the eruption have been debated among archaeologists for decades. One position holds that the eruption caused an abrupt and total cessation of human life in areas closest to the epicentre. A more recent school of thought has argued for local population survival, including in areas relatively proximate to the eruption. The research team determined that both of these interpretations were overly simplified. Populations did decline where ecosystems collapsed and areas became uninhabitable, but in some regions numbers actually rose in the period after the eruption. Lead author Enrico Crema, professor at Cambridge University, stated that while the disaster caused major loss of life, survivors responded by migrating, forming new social networks, adopting new economic strategies, and finding ways to persist and later recover under post-disaster conditions.

The study identified four distinct regional population patterns across prehistoric Japan. In southern Kyushu, Jomon forager populations were already declining before the eruption occurred, meaning the disaster affected a region that was already sparsely populated and frequented primarily by highly mobile groups. In northern Kyushu, populations had been growing prior to the event, and that growth trend continued through the disaster and its aftermath despite significant and lasting ecosystem damage. The authors suggest this continued growth may reflect movement of displaced persons out of the most severely affected zones immediately following the eruption. Inland survivors appear to have relocated to northern coastal areas, where marine ecosystems recovered relatively quickly, with population growth potentially accelerated by an increased reliance on marine resources. In more distant parts of Japan, regions that had seen population growth before the eruption experienced demographic stagnation or decline afterward. The study notes these far-reaching effects had not been previously identified and may be linked to short-term climate changes triggered by the eruption, to severe tooth attrition observed in deer and boar populations — animals central to Jomon subsistence — possibly resulting from grazing on ash-covered landscapes, or to a range of other volcanic impacts on human health and wellbeing.

Jordan stated that the research demonstrates how unpredictable and complex the aftermath of a major disaster can be, and that even in extreme circumstances, survivors and communities retain limited choices and must act, adjust, and establish new connections and social networks.