Geosite determination based on geodiversity assessment utilizing the volcanic history of a near-sea-level explosive eruption-dominated volcanic island: Tūhua/Mayor Island, New Zealand

Abstract

Abstract Tūhua/Mayor Island is located approximately 45 km off the NE coast of the North Island of New Zealand. This island was formed by various explosive and effusive volcanic eruptions commonly influenced by magma–water interaction eruption events occurring since the Pleistocene. The wider area of the SW Pacific contains numerous volcanic islands with a similar type of volcanic evolution. Tūhua/Mayor Island should be studied in more detail to understand the underlying volcanic mechanisms and apply this research to other volcanic islands in the SW Pacific. Mayor Island, also known by its indigenous Māori name Tūhua (obsidian in Māori), provides an ideal site for studying current volcanism. The present day island was formed around 150 ka ago and contains several rhyolitic lava-flows from different time periods, pyroclastic-flow deposits generated by small-volume localized eruptions and ignimbrite deposited by large explosive eruptions. Our research utilized a qualitative–quantitative assessment of geodiversity estimates to highlight possible geosites for the collection of precise information about the geological evolution of this area, demonstrating the potential of geoeducational sites. The term geodiversity recognizes geological and geomorphological elements, which have shaped the Earth's surface and underly our abiotic environment. Additionally, volcanic heritage was included in our equation, specifically tailored for Tūhua/Mayor Island and based on expert views (qualitative model). This model allows for a wider diversity for the area of research compared with the original method, which utilized only geological elements. The results show that areas with pyroclastic deposits exposed on the cliffs and in the centre of the collapse caldera should be considered for the further study for geosite planning.