Karioi’s unique geology
Science field day - exploring Karioi’s geology
Did you know... Pirongia and Karioi first formed in near simultaneous eruptions? According to geologist Oliver McLeod, you could have stood at one and watched the other form. These eruptions resulted from large scale fault movements in the western North Island about 2.5 million years ago. Oliver, a passionate young geologist, is digging deep into the history of Karioi and creating a new geological map of Karioi. He’s funded this endeavor through Kickstarter, possibly the first major geological work to be crowdfunded!
Last month, Oliver took our volunteers on a walk at Te Toto Gorge and we learned how unique Karioi really is! Te Toto Gorge was formed by a landslide, probably causing a large tsunami. “One imagines that the same water trickling down its stream once permeated the edifice, soaking into the blue clays below. The clays swelled, in secret, and then yielded in a massive collapse event,” writes Oliver in his blog of our visit.
We looked closely at the rocks along the coast at the foot of the gorge, as Oliver decoded their stories for us. About half of Karioi is composed of ankaramite, a type of basaltic lava containing giant volcanic crystals. We got to see crystals of all colours: black clinopyroxene, green/rust-coloured olivine, and white plagioclase. We compared this to some grey and smooth rocks, a consequence of another type of volcanism. These two types of rock, and two types of volcanism, mark a significant fact about Karioi.
Karioi is composed of two contrasting types of lava, arc and intraplate, which globally represent two very different types of volcanism. This is a very rare phenomena, with only the two other volcanoes in the world showing this - Mt St Helens (USA) and Turrialba (Costa Rica). Te Toto Gorge is a great place to see the layers that represent these two types of volcanism, which challenges the way geologists have seen our world until now. We also learned about this from our geology talk with visiting geologist Maud Jordan last year.
We’re excited to follow Oliver’s work this year and look forward to his map. You can follow Oliver on his Kickstarter page.