This study investigates the geological origins and oral traditions of three groups of big boulders in Shizuoka Prefecture:
Yonaki-ishi at Sayo-no-Nakayana, Kakegawa City, the
treasure spheres of the Yaizu Shrine, Yaizu City, and the
Tamayura-sama at Tamatori, Fujieda City, from the perspective of cultural geology. These boulders, measuring up to one meter in diameter, are all calcareous concretions and derived from the Paleogene~Lower Miocene Setogawa accretionary complex exposed in the southern Akaishi Mountains, the easternmost SW Japan. Thus, they are largely autochthonous, remaining close to their sites of origin.
The
Yonaki-ishi shows a marked transformation in public perception. Following the emergence of an oral tradition concerning the murder of a pregnant woman, it shifted from an object of fear and curiosity to an obstacle on a busy road, to a commercial exhibition item, and finally to its current role as a memorial tower.
The two
treasure spheres of the Yaizu Shrine were historically revered as sacred symbols and believed to date back to about CE400, and have long been believed to have been carried by tsunami waves to the Tamatori area, as tsunami boulders, several hundred years after the shrine’s foundation.However, recent studies on the tsunami-inundation areas from the ancient earthquakes and the projected impact areas of future giant Tonankai earthquake suggest that this tsunami-transport belief is unlikely. Instead, the spheres were probably washed away into the Suruga Trough, and the
Tamayura-sama boulders at Tamatori area are more likely not tsunami-boulders, but all in-situ ones.
抄録全体を表示