After a Massive Undersea Eruption Buried Japan in Ash, Survivors Moved to the Coast

A new study suggests that people in prehistoric Japan were more resourceful after a catastrophic volcanic eruption than researchers had assumed. According to ScienceAlert, some regions were left uninhabitable for a very long time, but in others survivors moved, built new social ties and adopted new ways of making a living.

The eruption, known as Kikai-Akahoya, took place around 5250 BCE, almost 7,300 years ago, off the southwestern coast of Japan. The findings were published in the journal Science Advances by an international team of researchers.

What the eruption did

Magma and volcanic material burst from beneath the seabed in a series of blasts. The event scored 7 out of 8 on the volcanic explosivity index, ScienceAlert reported, and eruptions of that size happen about once every 500–1,000 years. It counts among the most destructive in history.

Archaeologist Peter Jordan of Lund University in Sweden said the eruption came with little warning. He described powerful earthquakes and enormous tsunamis that struck the Japanese islands, followed by meters of ash that covered the landscape. The people living there at the time were Jomon foragers.

Evidence of the eruption was first found in the 1970s, and scientists have argued ever since about its effects. The damage was clearly extensive, but it has been unclear whether and how fully nearby societies recovered.

How researchers tracked the aftermath

The team examined 540 existing archaeological samples from across Japan, dating from 8,000 to 6,500 years ago, which covers several hundred years on either side of the eruption. Many of the samples were radiocarbon-dated finds such as charcoal or bones.

By counting how many dated finds came from before and after the eruption in each region, the researchers estimated how active the local population was. This approach gives a picture of rising or falling human presence rather than a direct head count.

What they found

The results varied by place:

• Near the eruption: Traditional Jomon forager populations in southern Kyushu, the area closest to the blast, may already have been shrinking before it happened.
• Farther north: The size and number of communities in the north of the island were growing before the eruption, and that trend continued afterward. The study suggests this may reflect affected groups moving away from the disaster zone.
• Along the coasts: Marine life seems to have recovered fastest, and human movement followed. The researchers suggest inland survivors may have shifted to the coasts and adopted a different way of life.
• Ise Bay and other distant areas: Population growth there stopped and in some places reversed.

The team offered several possible explanations for the more distant declines. One is short-term cooling triggered by the eruption. Another is an as-yet-unidentified effect of climate change. A third is a loss of food sources: grazing in ash-covered landscapes may have worn down the teeth of deer and boar, shortening their lives.

What the researchers say about survival

Archaeologist Enrico Crema of Cambridge University said the disaster caused major loss of life. He added that survivors migrated, formed new social relations, developed new kinds of economy and appear to have found creative ways to later thrive in the changed conditions.

Jordan said survivors in even the most desperate situations still have choices, however limited. In his words, they must act, adjust, collaborate and find new connections and social networks.

Why it matters

The study gives a long-term look at how human societies respond to sudden natural shocks. ScienceAlert noted that this is increasingly relevant in a world facing major shifts in climate and weather. Jordan said the work deepens understanding of the contingent ways cultures and societies cope with sudden shocks and catastrophes.

The result also shows how uneven the effects of a single disaster can be. Some communities were wiped out or driven away, while others adapted, and still others farther away saw growth stall for reasons that are not yet settled. Because the method relies on counting dated finds, it points to broad regional trends rather than the fate of individual communities.

Around Prague, based on reporting by ScienceAlert