Palaeotsunamis and their influence on Polynesian settlement.

The 11 March 2011 TAhoku-oki tsunami caused widespread devastation to coastal communities in Japan. This event however was merely the latest, yet largest, of several similar occurrences in the Pacific that include the 2007 Solomon Islands, 2009 South Pacific and 2010 Chilean tsunamis. All have had their predecessors, and a growing data base of palaeotsunamis in the Pacific suggests recurrent events comparable with, and of larger magnitude than their recent historical counterparts. Here we show that evidence for regional palaeotsunamis provides an opportunity to re-evaluate hypotheses used to explain the punctuated history of human settlement patterns across the Pacific. In particular, the almost two millennia 'long pause' in eastward migration, and the abandonment of long distance sea-voyaging in the 15th century, may be related to palaeotsunamis, with potential sources including the tectonically active Tonga-Kermadec trench, the Kuwae caldera collapse, and the more distant Pacific-wide Ring of Fire. © 2012, SAGE Publications

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

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 1855 CE. 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 2095 cal. BP) and Palaeotsunami II (maximum date 915 cal. 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 (340 m) inferred from the deposits found in this study. Palaeotsunami III (maximum date 525 cal. 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. © 2017 Elsevier B.V

Return of the Sea Monster – a tale from D’Urville Island, New Zealand

Not available

The marine reservoir effect in the Southern Ocean: an evaluation of extant and new R values and their application to archaeological chronologies

The last phase of human colonisation of the south-west Pacific occurred around the 12th Century AD amongst the islands of the subtropical and temperate zones of the Southern Ocean (i.e., Norfolk Island, the Kermadec Islands, New Zealand and the Chatham Islands) (Fig. 1). Archaeological evidence indicates that initial colonisation of the region was rapid, possibly taking less than 100 years. Unfortunately, the chronology of these events has been largely reliant on charcoal radiocarbon determinations that have not been successful in delineating these changes. This paper investigates the use of marine shell for radiocarbon dating as an alternative to charcoal, with specific focus on variation in the marine 14C reservoir (specifically the ∆R) of Raoul Island (Kermadec Islands), Norfolk Island and Chatham Island (Fig. 2). Results from known-age, pre-AD 1950 shellfish indicate that ∆R values south of the South Pacific Convergence Zone are low compared to those recorded for islands within the South Pacific generally (Fig. 1) (see Petchey et al.in press). An average ∆R value of –19 ± 13 14C yr is recorded for Raoul Island and –49 ± 10 14C yr for Norfolk Island. These values are attributed to heightened absorption of atmospheric CO2 in this region. Extant published ∆R information from New Zealand (Fig. 2A) also suggests a low average ∆R value for these southern waters, but the range of values indicates that considerable variability is possible because of the complex interplay of currents around the New Zealand coastline. In contrast, results from Chatham Island are more variable and much higher (average ∆R = 134 ± 83 14C yr). Stable oxygen and carbon isotope data support the hypothesis that these ∆R values are caused by upwelling and mixing of 14C-depleted water along the Chatham Rise. Comparison of marine and charcoal 14C determinations from archaeological sites on Raoul Island support, within the limits of the available data, the ∆R values obtained, but further analysis is required to establish the stability of this value over time