On July 3, 2021, a debris flow caused by a landslide from an embankment occurred along the Aizome River in the Izusan area of Atami City, Shizuoka Prefecture, central Japan, and buried sabo dam which was located approximately 450 m downstream of the embankment. Shizuoka Prefectural Government sampled one 13.1-m long core of deposits buried in the sabo dam in late August 2021. In this paper, radiocesium concentration was measured and grain compositions was investigated for this core sample. As a result, 134Cs and 137Cs released from the Fukushima Daiichi Nuclear Power Plant in mid-March 2011 were detected, and these markers specified the depositional surface at mid-March 2011 at 3.95-3.85 m core depth. In addition, the occurrence of fragments of both mudstone and chert in the overlying sediments indicates that the 3.74 m-thick portion was definitely the debris flow deposit.
