HIROSHI MACHIDA AND SHINJI SUGIYAMA
This chapter addresses in detail the precise mechanisms by which a large volcanic eruption in Japan generated significant cultural change. The principal mechanism concerned appears to be that of landscape change, which made large-scale adaptation and readjustment necessary. The chapter illustrates the wide range of research tools which may be adopted to determine the relationship between an archaeological site and the hazards present in the natural environment.
Japan is a volcanically active area where explosive activities have distributed tephra deposits over extensive areas on numerous occasions. Many of the tephra layers play important roles as time-markers in establishing a chronology for the Quaternary. Artefacts and archaeological remains have been excavated from soils sandwiched between distinctive tephra layers. These marker layers are useful for dating and correlating deposits found in different areas, especially when the relative dating is confirmed by radiometric methods. In addition, the presence of the tephra layers suggests that explosive volcanism may have had a significant impact on physical environment, human societies and culture change in Japan.
Among the many large-scale eruptions during the Japanese Holocene period, the Kikai-Akahoya eruption was the biggest. The eruptive products from it are called the Kikai-Akahoya tephra (K-Ah) (Machida and Arai, 1978). The Kikai-Akahoya event has a Volcanic Explosive Index of 7 (Newhall and Self, 1982). In Japan and adjacent areas volcanic eruptions with VEIs of 4 and 5 are known for the historic period. However, with the one exception of the Changbaishan (Baegdusan) eruption, which took place on the northern part of Korean Peninsula during the latest period of the ninth century or the earliest of the tenth century (Machida et al., 1990), very large-scale activity with VEIs similar to the Kikai-Akahoya event are unknown. In this chapter we summarise the processes that took place during the Kikai-Akahoya tephra-forming eruption and assess the impact of the emplacement of the tephra and associated environmental changes on human societies. General features of this volcanic hazard and the resulting human disasters have been reported previously (Machida, 1984) and so the major