Discovery of a tsunami boulder along the coast of Shimoda, Shizuoka, Central Japan

Abstract

We found a boulder to which emerged sessile assemblages cling, 3.4×2.5×2.5m in size and estimated at 32 tons, on a wave-cut bench at Shimoda, Shizuoka, Central Japan. The emerged sessile assemblages are distributed at 0.7-2.2m above mean sea-level, and consist mainly of small barnacles, oysters, and polychaetes. Based on AMS ¹⁴C dating (AD 1720-1950) and the ecology of the emerged sessile assemblages, we conclude that the boulder was rolled to emergence by a tsunami associated with the AD 1854 Ansei-Tokai earthquake.