Year

2020

Degree Name

Bachelor of Science (Honours)

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Amy Dougherty

Abstract

The New Zealand coastline is susceptible to tsunami hazards from both regional and trans-pacific sources. With a coastal population only expected to increase over the coming decades, the risk associated with tsunami activity has seen a similar increase. The historical record for tsunami in New Zealand only extends back a mere 200 years and is too short to capture the range of tsunami that could potentially affect the coastline. In efforts to better prepare against future events, various paleotsunami studies have been undertaken across the New Zealand coastline to study tsunami that occurred before the historical record began. Despite this, a lack of well-preserved indicators within deposits has led to a scarcity in high-resolution evidence that has been well dated. This study utilises the preservation capabilities of the Omaha Beach barrier system that has built seaward (prograded) over the past ~ 6500 years, in order to identify viable evidence for a paleotsunami deposit as well as possible indicators as to its timing and origin. X-ray fluorescence analysis of pumices found throughout the barrier has found them to be sourced from both the Kermadec Arc region and the eruption of Taupo volcano. Consequently, it is concluded that they represent a Loisels pumice deposit analogous to others found along the eastern coast of North Island. The correlation of Loisels pumice to inferred ages of subsurface beachface signatures has concluded that a tsunami event occurred between ~1000 and 1800 BP. The presence of pumice across the southern ~ 4 m beach ridges and the absence of pumice within the northern ~ 6 m foredune ridges has allowed an inundation height of ~ 4 – 6 m to be inferred. Pebbles found among the pumice have been correlated to a Hjulstrom curve to allow a minimum flow velocity of ~ 170 cm/s to be determined. Conceptual models have been constructed to demonstrate possible scenarios whereby the pumice was deposited onto the barrier. This study represents the first time correlations between the chemical characteristics of pumice to the ages of ridges within a prograding barrier have been used as a proxy for a paleotsunami deposit. The promising results from this study demonstrate the potential of resolving the history of tsunami at Omaha. This inspires future work to be carried out with implications that the application of this unique approach to prograded barriers worldwide can provide increased understanding of paleotsunami events.

FoR codes (2008)

040601 Geomorphology and Regolith and Landscape Evolution, 040604 Natural Hazards

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.