A gigantic volcanic eruption shook Japan 7,300 years ago. Yet some nearby populations continued to grow.
At that time, communities lived by hunting, fishing, and gathering on the Japanese islands. Then Mount Kikai, south of the archipelago, erupted with exceptional force. Enormous quantities of ash covered the land, transforming the landscapes and depriving many inhabitants of their usual resources.
Map of the ashfall from the Akahoya eruption, originating from the Kikai caldera in southern Japan approximately 7,300 years ago. The contours indicate, among other things, thicknesses of 20 and 30 cm.
Map: Hugo Lopez (Yug), modified by Pekachu, CC BY-SA 3.0, via Wikimedia Commons.
Image Wikimedia
One might think that such a catastrophe caused the same collapse everywhere. In southern Kyushu, the island closest to the volcano, populations understandably declined sharply. But farther north, some communities instead continued to develop.
How can we trace people who lived several millennia ago? Researchers studied dates obtained from archaeological remains, notably through carbon-14 dating. When a region yields more evidence of habitation for a given period, this may indicate that it was more densely populated.
The method requires caution: some regions have been excavated more extensively than others. An international team therefore developed a statistical model capable of taking these differences into account while comparing demographic trends and the thickness of ash deposits.
The results show that the eruption’s consequences varied greatly from one area to another. In southern Kyushu, living conditions deteriorated abruptly. In the north, however, populations were able to continue growing despite the upheaval.
Why such a difference? People from the hardest-hit regions may have moved to less affected areas. Other communities may have adapted their habits to find food. Researchers are considering these explanations, but the remains do not allow them to directly track the movements of families.
The study also shows that the eruption’s influence did not stop at the lands covered in ash. In some more distant regions of Japan, population growth appears to have slowed. A catastrophe can therefore alter the lives of very different communities, even at a considerable distance.
These results above all show that, when faced with the same event, human populations can follow very different trajectories depending on local conditions and their ability to adapt.