Year

2020

Degree Name

Bachelor of Science (Honours)

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Amy Dougherty

Abstract

Coasts are important as they are dynamic and one of the most prone environments to the impacts of climate change. Sea level rise is one of the most significant issues of the present day and it will continue to evolve as a more critical issue in the future. Therefore, it is of utmost importance and urgency for coastal environments to be properly managed to best mitigate the effects on coastal hazards such as storms, sea level rise and occasionally tsunami. The successful management of coasts requires knowledge on how these hazards have affected environments in the past. Studying prograded barriers is an effective and reliable way to determine the occurrence of coastal hazards over millennial time scales. These barrier types accumulate seaward over time, and therefore allow preservation of storms, relative sea-level changes, and tsunami. Geological hazards such as earthquakes and volcanic activity are also an important consideration in tectonically active regions, and prograded barriers can also preserve records of these events. A combination of methods, which are Light Detection and Ranging (LiDAR), Ground Penetrating Radar (GPR), beach profiling, coring and radiocarbon dating have been applied on the prograded barrier, to determine the evolutionary history at Papamoa Beach, New Zealand. Digital Elevation Models (DEMs) derived from LiDAR, provide highresolution morphology that has been used to analyse storm occurrence and earthquakes. GPR and beach profiles have been used for analysis of the stratigraphic record to detect lower intensity storms, tsunami, relative sea-level changes, and earthquakes preserved in the stratigraphy. Coring was used to obtain radiocarbon dates and tephra deposits to allow calculation of progradation rates between specific time periods. The analysis revealed a relative sea-level stillstand between 6 and 4.5 thousand years ago (ka), followed by a decrease in relative sea levels from 4.5 ka to 1 ka, and a stabilisation in relative sea levels from 1 ka to present. These varying sea levels impacted progradation rates at Papamoa Beach, with progradation occurring at 0.288 to 0.774 m per year during the sea-level fall, and rates between 0.108 and 0.295 m per year during the stable sea-level phases. The effects of a 2.9 to 4.4 m subsidence from earthquake activity approximately 1.85 ka also contributed to slowed progradation rates, with progradation mainly around 0.12 m per year after that event. The timing of the earthquake closely correlates with the eruption of the Taupo volcano, showing a potential link between earthquakes and volcanoes. The barrier also showed an average storm recurrence interval of 1 in ~30 years preserved in the palaeo-beachfaces (stratigraphy). On the beach ridges (morphology), a pre-subsidence interval of 1 in ~125 years and a post-subsidence interval of 1 in ~300 years was recorded. A slightly flattened morphology may also indicate past tsunami activity. This study provides a detailed multi-hazard record and can be used for further research in both coastal and geological assessments. This will allow for more effective and informed management of coastlines in New Zealand. Furthermore, this approach of assessing multihazards along the coast can be extended to prograded barriers worldwide.

FoR codes (2008)

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.