Japan's Massive Volcanic Eruption Brought Collapse to Some Regions and Growth to Others

Keypoints:

• A Lund University-led study in Science Advances reexamines the Kikai-Akahoya eruption of about 7,300 years ago
• The eruption came from the Kikai caldera, about 30 kilometres south of Kyushu
• Researchers found four distinct regional population patterns among the Jomon hunter-gatherers
• Southern Kyushu's population was already declining before the eruption
• Northern Kyushu kept growing, possibly helped by refugees moving out of the worst-hit areas

Seven thousand three hundred years ago, a volcano exploded from the sea floor near southern Japan. The Kikai-Akahoya eruption was one of the largest of the past 11,700 years. Jomon hunter-gatherers lived across the archipelago at the time. A new international study led by Lund University asks what happened to those communities next.

Archaeologists had split into two camps. One side argued the eruption wiped out people across southern Japan. The other said communities survived even close to the blast. The new analysis finds both versions too simple. The team placed the eruption within long-term population trends, using radiocarbon dates and comparing them with pottery, tools, settlement evidence and volcanic ash deposits.

The results show four regional patterns. In southern Kyushu, Jomon populations were already declining long before the eruption. The large villages there had been abandoned several thousand years earlier. The region was sparsely populated and visited mainly by mobile groups, so the disaster hit a place that was already emptying.

Northern Kyushu looks very different. Its population had been growing, and growth continued through the eruption and its aftermath, despite lasting damage to ecosystems. The authors suggest refugees may have moved out of the worst-hit areas. Inland survivors appear to have clustered along northern coasts, where marine ecosystems recovered quickly. New ways of living built around the sea may have sped up growth.

The farthest regions show a quieter cost. Populations there had been growing before the eruption, then stagnated or declined afterward. The study notes these distant effects had not been identified before. Possible causes include short-term climate change, severe tooth wear in deer and boar from grazing on ash-covered land, and other health impacts.