Kikai-Akahoya eruption: how Japan's Jōmon societies survived the volcanic disaster

A catastrophe whose effects have long been debated

According to Lund University, the eruption emerged from the seabed with few warning signs. Powerful earthquakes, considerable tsunamis and ash layers several metres thick struck the Japanese islands, during a period when Jōmon communities lived by hunting, fishing and gathering.

For decades, archaeologists have debated the scale of the shock. Some have described an "apocalypse" that would have ended all human life near the epicentre, while others argue that local populations survived, sometimes close to the affected zone. The debate therefore concerned less whether damage occurred than its extent and duration.

A method based on demographic data

The researchers examined changes in population levels before and after the eruption, in order to move beyond the divide between total collapse and continuity. This approach makes it possible to distinguish regional trends rather than reasoning at the scale of the whole archipelago, which explains the complexity of the results.

According to the study, led by Enrico Crema, professor at the University of Cambridge, neither total collapse nor simple continuity accounts for the data. Populations did decline in some areas, but they sometimes increased elsewhere, reflecting divergent demographic responses.

Decline in the south, growth in northern Kyushu

In southern Kyushu, Jōmon populations were already declining well before the eruption. The region was sparsely populated and visited only by highly mobile groups, so the catastrophe struck an already fragile territory.

In northern Kyushu, by contrast, the population continued to grow during and after the disaster, despite lasting damage to ecosystems. The authors suggest that survivors, comparable to "refugees", left the most affected areas to regroup on the northern coasts, where marine ecosystems recovered rapidly.

Adapting to the resources of the sea

This growth was reportedly accelerated by new adaptive strategies centred on exploiting abundant marine resources. Survivors thus developed new forms of economy and social ties, still according to the study published in Science Advances.

Peter Jordan, professor of archaeology at Lund University and lead author, stresses that societies still have room for choice, even in extreme situations. They must adapt, cooperate and create new networks in order to recover, a lesson that goes well beyond the Japanese case.

Distant effects still puzzling

In regions farther from the eruption across Japan, the population, which was rising before the eruption, stagnated or even declined after the catastrophe. These distant effects had never been identified before, according to the researchers.

Several hypotheses are proposed: a short-term climate change caused by the eruption, severe tooth wear in the deer and wild boar on which the Jōmon depended, probably linked to grazing on landscapes covered in ash, or other volcanic impacts on human health. These leads remain to be verified by further research.