古墳時代の火山災害
群馬県同道遺跡の発掘調査を中心にして
1989 年 27 巻 4 号 p. 283-296
詳細
1989 年 27 巻 4 号 p. 283-296
The three layers of tephra that erupted from Haruna (_??__??_) volcano and Asama (_??__??_) volcano covered most of the rice fields in the district of Gunma in the Kofun period (from 4c to 6c A. D.). So considerable damage might have been done to the society of that time. The writer of this report wants to make clear what measures the rulers managed to take against these volcanic disasters. We have no historical records of the volcanic activities in Japan prior to the Kofun Period because of the lack of written records. But we can determine the time or the season of tephra effusions by archaeological means, mostly typological methods of analyzing pottery from the horizons both above and below each of the three tephra layers.
The time and the season of tephra effusions that the writer has conclusively identified are as follows.
1) The tephra in the lowest horizon (Asama C pumice: As-C) had erupted in the late autumn of the middle of the 4c A. D. from Asama volcano; footmarks of cultivaters or planters on the muddy paddy fields and morphologic plans of the rice fields remaining just below each of the three tephra layers prove this.
2) The tephra in the middle horizon (Haruna Futatsudake (_??__??__??_ )ash: Hr-FA) erupted in the early summer of the beginning of 6c A. D. from Haruna volcano.
3) The tephra in the uppermost horizon (Haruna Futatsudake pumice: Hr-FP) erupted in the early summer of the middle of 6c A. D. At Dodo (_??__??_) Site in Gunma Pref., we found four horizons of rice fields just below the tephra layers; three horizons were proved to be in the Kofun Period; quite the same rectangular divisions of rice field were found from the horizons both above and below each of the three tephra layers.
This fact shows that the rice fields had never been abandoned since then but were cultivated further on the tephra layers. The writer thinks that the rulers of that time forced the people to restore the rice fields injured in the volcanic disasters, immediately after the effusion, in order to keep their systems of control or maintain their bases of food production.
