Shaun Williams

Tsunami runup and tide-gauge observations from the 14 November 2016 M7.8 Kaikōura earthquake, New Zealand

The 2016 Mw 7.8 Kaikōura earthquake was one of the largest earthquakes in New Zealand’s historical record, and it generated the most significant local source tsunami to affect New Zealand since 1947. There are many unusual features of this earthquake from a tsunami perspective: the epicentre was well inland of the coast, multiple faults were involved in the rupture, and the greatest tsunami damage to residential property was far from the source. In this paper, we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast, then present tsunami tide gauge and runup field observations of the tsunami that followed the Kaikōura earthquake. For the size of the tsunami, as inferred from the measured heights, the impact of this event was relatively modest, and we discuss the reasons for this which include: the state of the tide at the time of the earthquake, the degree of co-seismic uplift, and the nature of the coastal environment in the tsunami source region.

Characterising diagnostic proxies for identifying palaeotsunamis in a tropical climatic regime, Samoan Islands

The September 2009 South Pacific Tsunami (2009 SPT) in the Samoa Islands resulted in local public and national calls to improve understanding of the medium- to long-term risks of tsunamis in these islands in order to further mitigate their impacts. This research addresses some of these calls through an interdisciplinary palaeotsunami investigation. Historical data beginning in 1837 indicate that the Samoan Islands have been impacted by tsunamis from all the major tsunamigenic zones within the Pacific Rim of Fire, making it an ideal location for starting to understand tsunami frequency and distribution within this region. Furthermore, the region has an historical record of extreme tropical cyclones.

Flank-Collapse on Ta’u Island, Samoan Archipelago: Timing and Hazard Implications

A discrepancy between the cartographic depiction of Ta’u Island, Samoan archipelago, in 1849 and its present geomorphology, leads to the impression that a massive collapse involving an estimated 30 km3 occurred on the island’s southern flank less than 170 years ago. It is likely that this flank-collapse, whenever it occurred, generated a tsunami with regional impacts. Here we apply exposure dating to the remnant landslide scarp using the cosmogenic nuclide 36Cl, to show that the flank-collapse occurred 22.4 ± 1.8 ka during the last glacial maximum (LGM). The collapse may have been triggered due to volcanic-related processes, but it is also possible that climatic-eustatic sea-level during the LGM may have played a role in influencing failure of the flank. We confirm that the initial cartographic depiction of Ta’u in 1849 was incorrect, and that this prehistoric landslide-tsunami was not a societal hazard at the time of its occurrence. This is because the Samoan and surrounding Island Nations were only inhabited about 3 ka or so. Nevertheless, we suggest that geomorphic features similar to the Ta’u flank-collapse on analogous islands and seamounts in the Pacific likely represent signatures of landslide-tsunamis in the past. We conclude that there is a need to identify and date other such features in the Pacific, in order to further improve our spatial and geochronological understanding of these events. There is also a need to identify flank features that have not yet failed, and assess the likely mechanisms that could potentially trigger failure. By doing this, we can start assessing with more confidence the hazard potential of similar flank-collapses in future—a risk that is presently under-represented.

Deep Charcoal Found at Fagali’i Village, Upolu Island, Samoa: Natural or Anthropogenic in Origin?

While it is generally accepted that Lapita groups reached West Polynesia ca. three millennia ago, there are very few archaeological sites in Samoa that date back this early. The one exception is the Mulifanua site in NW Upolu from which a turtle bone associated with a Lapita pottery deposit was dated to 2,970–2,640 cal BP (NZA-5800 [2σ ]; 2,838– 2722 cal BP [1σ ]). This is currently the only and earliest 14C age related to prehistoric human settlement in Samoa (Cochrane et al. 2013; Petchey 2001; Rieth and Hunt 2008) (Figure 1).

Reassessing the environmental context of the Aitape Skull – The oldest tsunami victim in the world?

There is increasing recognition of the long-lasting effects of tsunamis on human populations. This is particularly notable along tectonically active coastlines with repeated inundations occurring over thousands of years. Given the often high death tolls reported from historical events though it is remarkable that so few human skeletal remains have been found in the numerous palaeotsunami deposits studied to date. The 1929 discovery of the Aitape Skull in northern Papua New Guinea and its inferred late Pleistocene age played an important role in discussions about the origins of humans in Australasia for over 25 years until it was more reliably radiocarbon dated to around 6000 years old. However, no similar attention has been given to reassessing the deposit in which it was found—a coastal mangrove swamp inundated by water from a shallow sea. With the benefit of knowledge gained from studies of the 1998 tsunami in the same area, we conclude that the skull was laid down in a tsunami deposit and as such may represent the oldest known tsunami victim in the world. These findings raise the question of whether other coastal archaeological sites with human skeletal remains would benefit from a re-assessment of their geological context.