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How to map an ancient stratovolcano

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How to map an ancient stratovolcano

5 May, 2022

Photo of Karioi maunga. Photo by Lloyd Homer GNS Science.

Photo of Karioi maunga. Photo by Lloyd Homer, GNS Science.

The ancient volcano Karioi rises above the black sands of Raglan, the iconic surf town on North Island’s west coast. Between turquoise swell and emerald-green forest, its immense cliffs of basalt lava and ash tell a story of past eruptions over two million years ago.

For the past six years, Dr Oliver McLeod has dedicated his time to meticulously mapping and sampling Karioi and its sister volcano Pirongia, which together form the two largest peaks in the Alexandra Volcanic Group between Te Awamutu and Raglan.

Equipped with traditional field gear – the rock hammer and hand lens – and more modern devices (GPS and drone), he sets out each week in search of new discoveries for his geological maps.

Each field trip is different. Weather ranges from icy cold and thundery in winter, to scorching hot in the summer months. Days are spent climbing through forested valleys and peaks or wandering lonely stretches of coastline between tides.

Karioi maunga is culturally revered by the Tainui people, who have a 700-year history of settlement on the slopes and harbours surrounding the volcano. Remnants of stone gardens for kumara and taro, set among hand cut drainage ditches, and storage pits in sand dunes are all common features of the maunga.

Karioi is one of only three volcanoes on Earth where the subduction-related volcanism and intraplate-volcanism have occurred together at the same time. It’s like Ruapehu and Tahiti combined into one volcano.

Dr Oliver McLeod Researcher for the MacDiarmid Institute

Dr McLeod says one of his biggest moments was presenting the Pirongia map to the Māori Kingi Tūheitia on behalf of Ngāti Maniapoto, at Purekireki marae in 2020.

“To be in the company of hapu who shared an equal or deeper appreciation of the Pirongia maunga left an impression on me. Every peak and stream has a name, and a story, which relate back to the tangata whenua and their generational experience of the maunga.”

Originally from Auckland, Dr McLeod completed his Honours degree at the University of Otago in Applied Geology, studying the Dunedin Volcano. After a year in Mexico observing eruptions at Colima Volcano, he returned to complete a PhD at the University of Waikato.

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Dr Oliver McLeod in the field

“While in Mexico, I had a kind of vision to study the geology of Pirongia. I considered Pirongia one of the last geologically unexplored places in Aotearoa New Zealand”.

Now working as a researcher for the MacDiarmid Institute alongside Diane Bradshaw (Stakeholder Partner Iwi) of Ngāti Te Wehi, Ngāti Mahuta, Ngāti Maniapoto, Waikato Tainui, Dr McLeod is excited about the next phase of the work.

“In 2021, we studied taonga at Kawhia together, matching toki/adze with their source rocks from the region. We were astounded to find how many rocks were brought in from Motutapu and Rangitoto ki te Tonga (D'Urville Island)."

Dr McLeod says he aspires to be a professor of Geology, whose research will encompass the materials and cultures of the South Pacific. Future aside, he fully embraces the present moment to complete his maps while the research world recovers from the pandemic.

The new work Geology of Karioi Maunga, Aotearoa-New Zealand will be published by the Geoscience Society of Aotearoa New Zealand in mid-2022. The publication includes a large printed geological map and illustrated full-colour explanatory text. Public lectures are planned
for Wellington, Auckland and the Waikato Region, dates to be announced.

To be young, to map mountains, and to do it with complete conviction and passion. This time will never be repeated.

Dr Oliver McLeod Researcher for the MacDiarmid Institute