Abstract
On July 3, 2021, a debris flow occurred due to the collapse of an embankment located at the headwaters of the Aizome River in Atami City, Shizuoka Prefecture. In this study, diatom assemblages were analyzed from three sites: an uncollapsed black soil (site B1) and brown soil (site B2) within the embankment, and a debris-flow deposit at site A2. The results revealed that each of the three sites exhibited distinct assemblage compositions. Notably, both inner bay and open-ocean diatom taxa were detected exclusively in the debris-flow deposit. These findings indicate that the composition of diatom assemblages is a useful indicator for classifying debris-flow deposits.
