Reciting the layers: Evidence for past tsunamis at Mataora-Wairau Lagoon, Aotearoa-New Zealand

• Published in: Marine geology 2017-07, Vol.389, p.1-16
• Main Authors: King, D.N., Goff, J.R., Chagué-Goff, C., McFadgen, B., Jacobsen, G.E., Gadd, P., Horrocks, M.
• Format: Article
• Language: English
• Subjects: Archaeology; Geochemistry; Microfossils; Māori; New Zealand; Palaeotsunami; Tsunami
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2017.05.001

Sedimentary, geochemical, microfossil and geochronological analyses were carried out on 10 sediment cores across the south-eastern corner of Mataora-Wairau Lagoon (M-WL), South Island, Aotearoa-New Zealand. This multi-proxy approach provides strong evidence for three late Holocene palaeotsunamis (two previously unreported) and a historical tsunami generated by rupture of the Wairarapa Fault in 1855CE. The main scientific evidence for these events consists of anomalous, high-energy marine sediment layers that overlie material of contrasting composition. These layers coincide with peaks in planktonic and benthic marine to brackish-marine diatoms and geochemical signatures indicative of sudden changes in environmental conditions. Palaeotsunami I (maximum date 2095cal.BP) and Palaeotsunami II (maximum date 915cal.BP - previously identified by Clark et al., 2015) appear to represent large events contemporaneous with major earthquakes inducing tectonic uplift and coseismic subsidence around the Cook Strait region. Palaeotsunami II is close to the date of the earliest settlement of the M-WL area by Māori, and a traditional narrative that references loss of life following waves over-washing the Wairau boulder bank. Given the boulder bank was likely to have been seaward of its current position during events I and II, we surmise that the inundation distances would have been greater than the most landward extent (340m) inferred from the deposits found in this study. Palaeotsunami III (maximum date 525cal.BP) was associated with tectonic subsidence across the study site, most likely associated with rupture of the southern Hikurangi subduction zone. We expect the ongoing refinement of the methods used in this study, and the results from future studies of analogue sites and offshore fault systems, will improve our understanding of the significant tsunami hazard facing this region. •Māori oral tradition refers to experience with extreme environmental disturbance.•Detailed record of past tsunamis preserved within a salt marsh environment•Multi-proxy evidence for three late Holocene palaeotsunamis and one tsunami in 1855CE•Sources capable of inducing tectonic uplift, coseismic subsidence, submarine landslides•Benefits to cross-disciplinary research in tsunami hazards science