Multi-proxy records of regionally-sourced tsunamis, New Zealand

A multi-proxy study of sediment cores from Kaituna Bay, Mimiwhangata, in northern New Zealand has produced a record of three palaeotsunamis, dated to around 6500 cal yr BP, 2800 cal yr BP, and 1450 AD. These events punctuate a coastal palaeoenvironmental history spanning the last 8000 years or more in which the site progressed from a semi-open lagoon to a freshwater swamp. Proxies used included stratigraphy, geochemistry, palynology, diatoms, foraminifera, geomorphology, and a regional palaeotsunami synthesis. The identification of tsunamigenic sources for these events is tentative. We propose that the two oldest events are associated with a source in the Tonga–Kermadec Trench region, with the most recent possibly associated with the Kuwae caldera collapse in 1452/1453 AD. Palaeotsunami deposits contemporaneous with the estimated age of the three events identified in this study were used to assist in identifying possible source regions. The development of regional and national palaeotsunami databases is in its infancy, but as more data become available, the ability to determine the source, magnitude and frequency of past events will improve. This will greatly enhance our understanding of the regional risk from tsunamis.