A massive eruption buried parts of southern Japan in ash 7,300 years ago, and the sea may have saved survivors
About 7,300 years ago, a volcano that now sits mostly beneath the sea off southern Japan tore itself apart. A new study suggests the eruption emptied large parts of Kyushu, yet communities on the island’s northern coast kept growing. The sea may have helped them do it.
A giant caldera off Japan’s coast
The Kikai caldera lies about 30 kilometers off the southern coast of Kyushu, Japan’s third-largest island. It measures roughly 19 by 17 kilometers, and most of it lies underwater. The Kikai-Akahoya eruption came as a series of increasingly powerful blasts separated by quieter periods, and it ended with the collapse of the caldera. Researchers rank it among the largest eruptions of the past 12,000 years.
At the time, Jomon people lived across the region. They hunted, fished and gathered plants. For years, archaeologists have debated what the eruption did to them. Some argued it wiped out local populations, an idea sometimes called the “Jomon Apocalypse.” Others doubted that the damage reached so far.
How researchers counted people without a census
An international team led by Enrico Crema at the University of Cambridge, with senior author Peter Jordan at Lund University, published the work in Science Advances in October 2026. They used radiocarbon dates from archaeological sites as a stand-in for population size. More dates in a period generally means more people leaving datable material behind.
The team divided Japan’s four main islands into 61 hexagonal study areas. Bayesian models then tracked how date frequencies changed in the 750 years before and after the eruption. Shorter and longer windows of 500 and 1,000 years served as sensitivity checks. The researchers compared the trends with pottery, tools, settlement evidence and ash deposits.
Decline in the south, growth in the north
The results split sharply by region. Southern and central Kyushu showed a strong drop after the eruption, and some areas may have been abandoned. Population in the south had already started to fall before the eruption, so the blast was not the only pressure. Meanwhile, the northern Kyushu coast kept growing, and so did parts of northern Honshu.
The harm to people in the south was likely severe. Ash could contaminate food and water, fine airborne particles could damage lungs, and high fluoride levels could poison the environment. Deer and wild boar, important food animals, may have disappeared from ash-covered land. Crema said the disaster caused major loss of life, but that survivors “forged new social relations.”
Clues that point to the sea and to migration
Two artifact types help explain the northern growth. First, stone harpoon points became more common and spread over a wider area of northern Kyushu after the eruption. Marine ecosystems probably recovered faster than ash-buried forests, so fishing and sea hunting could have offered a more dependable food supply. Some of this harpoon trend began before the eruption, which means the volcano may have sped up a shift already under way.
Second, slit stone earrings tell a story about movement. Archaeologists found these ornaments in southern Kyushu before the eruption. Afterward, they began appearing at sites along the northern coast. The authors read this as a possible sign of migration, exchange or new alliances. Coverage of the study also notes a new pottery style in the north, which fits the idea that newcomers arrived.
What this changes, and what it does not
The study suggests that neither extreme view fits. The authors say the model only partly supports the Jomon Apocalypse idea, and only for southern and central Kyushu. Jomon societies neither collapsed entirely nor simply carried on. Many people probably died, while others adapted, moved and built new ties.
Several caveats remain. Radiocarbon dates give an indirect measure of population, not a head count. Continued growth in a region does not mean it escaped disruption. Thick ash can bury sites, and survivors may have settled in places that archaeologists have sampled less. Ash depth did not fully explain which regions suffered most. The researchers also did not directly test mechanisms such as cooling, health effects or the loss of game. The idea that northern growth came partly from refugees remains a hypothesis.
Even so, the picture is hopeful in a careful way. After one of the largest eruptions of the past 12,000 years, people did not simply vanish. Some of them seem to have walked north and looked to the water.