Multi-proxy evidence for trans-Pacific tsunamis in the Hawaiʹian Islands

The origin of two sand layers buried in Pololū wetland, on the northeast coast of the island of Hawaiʹi, was investigated using a multi-proxy approach, including radiometric dating, sedimentology, geochemistry, micropalaeontology, palynology and historical records. Based on 210Pb, 137Cs and pollen data, the lower sand unit extending 250 to 350 m inland is attributed to the 1946 Aleutian tsunami, while the upper sand unit was laid down by the 1957 Aleutian tsunami. Chronological information does not appear to support any link between these deposits and historical storm events. Furthermore, sedimentological, geochemical, diatom and pollen results suggest deposition of marine and near-beach sediments under high energy conditions typically associated with tsunami inundation. This work presents the first conclusive sedimentary evidence for distantly-generated tsunamis on the Hawaiʹian Islands, opening the way for more comprehensive historical and palaeotsunami studies. Indeed, a brief review of archaeological data suggests that the Hawaiʹian coast may have experienced similar large magnitude events in the past, from both local and distant sources.