Storm Waves May Be the Source of Some "Tsunami" Coastal Boulder Deposits.

Coastal boulder deposits (CBD) provide what are sometimes the only remaining signatures of wave inundation on rocky coastlines; in recent decades, CBD combined with initiation of motion (IoM) analyses have repeatedly been used as primary evidence to infer the existence of ancient tsunamis. However, IoM storm wave heights inferred by these studies have been shown to be highly inaccurate, bringing some inferences into question. This work develops a dimensionless framework to relate CBD properties with storm-wave hindcasts and measurements, producing data-driven relations between wave climate and boulder properties. We present an elevation-density-size-inland distance-wave height analysis for individual storm-transported boulders which delineates the dynamic space where storm-wave CBD occur. Testing these new relations against presumed tsunami CBD demonstrates that some fall well within the capabilities of storm events, suggesting that some previous studies might be fruitfully reexamined within the context of this new framework.