After a Super Volcanic Eruption: a new project on social-ecological impacts of the Kikai-Akahoya disaster, 7,300 years ago

Major volcanic eruptions, alongside large earthquakes, are one of the most devastating and unpredictable natural disasters past and present and one of the major future threats for the society. Located in the western portion of the Pacific “Ring of Fire”, the Japanese Archipelago is one of the most geologically active areas in the world and has historically experienced many large-scale volcanic eruptions and earthquakes. Of such disastrous events, the Kikai-Akahoya (K-Ah) eruption, which occurred in the southern sea of Kyushu approximately 7,300 years ago, was the most devastating event in the past 10,000 years (Figure 1).

Figure 1. Map with the range of the K-Ah tephra represented by the thickness of tephra layers. Based on Machida & Arai 2003: figure 2.1-2.(町田 洋、新井房夫 2003『新編 火山灰アトラス』東京大学出版)

However, its social-ecological impacts have still remained largely unknown. Those include what area was affected, in what ways and on what scale, by the eruption? How did people react to the disaster? How long did the effects continue? An international team of archaeologists and volcanologists, including the author and researchers from University of Groningen, Lund University, Stockholm University and Kyushu University, has recently launched an interdisciplinary project to investigate the cultural influence of K-Ah and started preliminary field research in relevant areas in Kyushu.

Figure 2. K-Ah tephra layer detected at the excavation of the Aihara No.1 site (the orange band in the middle of the layer section on the left), Miyakonojo City, Miyazaki Prefecture (September 2020). A 40cm-thick tephra layer packed the lower cultural assemblage belonging to the period before the Todoroki pottery tradition (on the right). Photo by the author.

K-Ah was a massive caldera-forming eruption that had a VEI (Volcanic Explosivity Index) of 7, making K-Ah one of the top 6 “super-eruptions” which have happened on earth in the present Holocene Epoch that began about 12,000 years ago since the Last Glacial ended. Pyroclastic flows covered the area within about 50 to 150 km from the volcanic epicentre, suggesting that communities in the southernmost part of Kyushu were eventually swept away, and induced major tsunamis in far more wide-ranging coastal regions. K-Ah produced more than 100 km3 of tephra, which rained down over 2 million km2 of most of Japan and the southern part of the Korean Peninsula (Figure 2).

Volcanic dust released in the air may have caused a global cooling in climate. All these caused huge damage to the natural environments that people depended on. Dated to 7,300 years ago, this apocalyptic event occurred during the Jōmon period when the society was based on a hunting-gathering economy, with wide usage of ceramic vessels, from about 16,500 to 3,000 years ago. Its impacts must have largely been felt by Jōmon communities, thriving on the rich forestry ecosystems.

The full scale of the K-Ah event was confirmed in the 1970’s, triggering intense debate within Japanese Archaeology about its immediate and longer-term impacts on Jōmon trajectories in Kyushu and beyond. Earlier consensus accepted complete annihilation of Jōmon populations in most of Kyushu, followed by resettlement of empty wastelands by surviving groups in the north, where nut-bearing forests recovered quickly. This disaster-driven population displacement model was justified by the apparently abrupt termination of the Hiragakoi-Senokan (H-S) pottery tradition, which had centred in southern Kyushu.

More recently, this population replacement model has been challenged by new research, demonstrating significant cultural continuity in much of Kyushu after eruption, indicating higher levels of survival closer to the eruption. Importantly, it became clear that the H-S tradition had already ended prior to K-Ah, and that the extended Todoroki tradition was already well established in southern Kyushu immediately prior to the eruption. The entire Todoroki tradition extends from 7,700 through to 6,300 years ago, and thus spans the period prior to, and also immediately after, the K-Ah impacts. Consequently, local populations must have survived in areas relatively close to the eruption. Specifically, the new research identifies that the Nishinozono sub-type pottery tradition that had started prior to K-Ah was maintained throughout the eruption and the direct aftermath and persisted beyond (Figure 3).

Figure 3. A deep bowl of the Nishinozono “Survivor” ware from the Egonokuchi site, Hiji Town, Ōita Prefecture. Nishinozono is one of the sub-types of the Todoroki tradition and was the tradition maintained by surviving communities. Photo by the author under the permission of the Ōita Prefectural Archaeological Centre (March 2021).
Figure 4. Central crater of Mt Aso (Mt Naka-dake), Kumamoto Prefecture. Mt Aso is the largest active volcano in Japan, having continuously emitting smoke and occasional eruptions. Photo by the author (September 2020).

There remain questions about how the populations survived through the disaster. Even so, it is important to note that sites of the Nishinozono tradition and its immediate successor are relatively smaller in scale, with limited cultural assemblages. They also tend to cluster in coastal regions, probably reflecting a shift towards marine resources and the reduced importance of terrestrial resources in damaged inland environments. These successful maritime focused lifeways then continued after the Todoroki tradition (so after 6300 years ago). The subsequent Sobata pottery group (about 6,300-5,500 years ago) originated in northern Kyushu, centred in coastal regions, and extended its distribution from southernmost Korea down to the Okinawa Islands. Thus, it is possible that K-Ah left lasting inland environmental damage and communities survived by intensified marine resource exploitation and by developing a wide extensive inter-regional network, mutually supporting each other until well over a millennium after the catastrophic eruption.

The research project has just begun and much more work is needed for a holistic understanding the long-term effects of K-Ah. Although recent years see major progress in volcanic impacts on past societies, almost all this work has focused on urban or settled agricultural societies like Pompei, but not on prehistoric hunting-gathering communities. Research on the K-Ah impacts could also be compared with those of similar events outside East Asia, such as the Laacher Zee event in Germany dated to about 13,000 years ago, which corresponds to the boundary from the Palaeolithic to the Mesolithic in Europe. International and interdisciplinary work on past disasters will offer numerous significant suggestions for the present society to increase resilience to future crises (Figure 4).

Uchiyama Junzo
Academic Associate, Sainsbury Institute

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