Formation process of the gravel‐dominated deposit from the 2011 Tohoku‐oki tsunami in Ofunato, northeastern Japan, inferred by integrating sedimentology and tsunami modelling

ABSTRACT Tsunami deposits serve as geological records of past events and are essential for understanding the occurrence and dynamics of tsunamis. However, conventional research has largely focused on sandy and boulder deposits, leaving gravel‐dominated tsunami deposits comparatively underexplored; furthermore, their characteristics and formation processes remain poorly understood. This study examined the characteristics and formation processes of a gravel‐dominated tsunami deposit generated by the 2011 Tohoku‐oki tsunami in Ofunato, northeastern Japan, using a combination of sedimentological analysis (roundness and imbrication of gravel clasts) and numerical modelling based on high‐resolution topographic data acquired by light detection and ranging (LiDAR). The gravel‐dominated tsunami deposit is characterised by landward thinning and slight coarsening accompanied by a decrease in the proportion of rounded beach gravel clasts; the gravel clasts were inferred to have been transported predominantly as bedload. Moreover, although not all run‐up and return flows are necessarily recorded, the imbrication of gravel clasts was found to preserve the sequence of tsunami flows in a semiquantitative manner. These results suggest that the sedimentological characteristics of gravel‐dominated tsunami deposits can serve as indicators for reconstructing their formation processes and tsunami flow conditions. The research strategy presented here provides a valuable framework for investigating tsunami deposits on gravel‐dominated coasts worldwide.