Geological map subject of talk

Waikato Volcanologist Oliver McLeod is visiting the Te Awamutu Library tomorrow talk about his 500 km2 geological map of Mt Pirongia, which he has spent three years making. The map unravels details of the volcano’s birth, growth and eventual collapse over its onemillion-year active lifespan.

Oliver is a PhD student and field scientist, who uses and admires traditional fieldwork methods.

In order to create the map, Oliver has completed more than 50 separate field surveys — all by foot — often doing 12-hour days and carrying 20-40kg of rocks home.

His ground-based geological surveys map volcanic stratigraphy — the layers of rock and the processes that created them.

Oliver relies on the simple field tools of a GPS, camera, field notebook, compass clinometer for measuring the orientation of rock and small magnifier, called a hand lens, for identifying rocks in the field.

He also uses a hammer to break hard basalt rocks.

Oliver’s mapping has revealed new information about the previously poorlyunderstood mountain.

“The map marks a point in our relatively young scientific history of New Zealand volcanoes,” he says.

“It provides a snapshot in time of our understanding of how volcanoes work, and how they are formed.”

His map suggests Pirongia's eruptive history was more explosive than previously recognised.

It updates the interpretation of Pirongia as a shield-type volcano, to a complex stratovolcanic system with numerous overlapping eruptive centres.

■ Oliver is speaking at the Te Awamutu Library on Wednesday, September 18 at 6.30pm.