Abstract
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.
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Acknowledgments
We thank Rhea Workman for her help in the initial conception of this study. We also thank Leilua Mase Akapo, Peter Craig, Rise Hart, Paul Brown, Leoso Leoso, Dino Ta’aga, Tavale Ta’aga, Ionatana Lealamanu’a, Koli Maeata, Douglas Fenner, Anekant Wandres, Janet Warburton, John Southward, Pat Roberts, Joan Williams, Jim Williams, Cathy Higgins, and Alison Green for their help and advice regarding field logistics in 2008. The National Park of American Samoa is also thanked for permitting us to conduct research in the Ta’u National Park.
The field component of this study was funded in 2008 by NZAID and the Mason Trust, University of Canterbury. The exposure dating was implemented via collaboration between the Department of Geological Sciences, University of Canterbury, and Geography, University of Exeter.
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Williams, S.P., Davies, T.R., Barrows, T.T., Jackson, M.G., Hart, S.R., Cole, J.W. (2014). Flank-Collapse on Ta’u Island, Samoan Archipelago: Timing and Hazard Implications. In: Sassa, K., Canuti, P., Yin, Y. (eds) Landslide Science for a Safer Geoenvironment. Springer, Cham. https://doi.org/10.1007/978-3-319-04996-0_89
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DOI: https://doi.org/10.1007/978-3-319-04996-0_89
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