A massive underwater volcanic eruption that struck Japan about 7,300 years ago did not simply wipe out or spare prehistoric communities, according to a new study led by Lund University. The Kikai-Akahoya eruption buried landscapes in meters of ash and triggered earthquakes and tsunamis, but its demographic aftermath varied sharply across the Japanese islands.
The researchers found that southern Kyushu's Jomon population had already been shrinking before the eruption, while northern Kyushu's population was growing and continued to do so through the catastrophe and afterward. They suggest that migrants fleeing the most devastated areas may have contributed to that growth, and that survivors who moved toward the northern coast found renewed food resources as marine ecosystems recovered.
More surprisingly, regions far from the volcano also experienced population changes, with prior growth stalling or reversing. The authors propose possible causes such as temporary climate disruption, ash-induced tooth wear in deer and wild boar, or other health effects. The findings, published in the journal, challenge the two dominant theories of either near-total apocalypse or widespread survival, showing instead a complex mix of decline, migration, adaptation, and growth.