Understanding our nearshore island volcanoes - Whakaari and Tūhua

A multi-year research project aims to find out the risks from two Bay of Plenty offshore island volcanoes: Tūhua / Mayor Island and Whakaari / White Island

In the National Isotope Centre in Gracefield, Jacqueline Grech Licari is bent over half a sediment core section, carefully looking for a dark line of ash - a clue left behind by Whakaari, a volcanic island in the Bay of Plenty.

Tracing the history of past eruptions

Jacqueline is a PhD candidate at Te Herenga Waka Victoria University of Wellington using sediment collected from the seabed around Whakaari, White Island, and its neighbour, Tūhua, Mayor Island to investigate their eruptive pasts.

Layers of ash - also called tephra - are carefully logged and sampled. Chemical analysis identifies exactly which volcano it came from, while the thickness of the layer gives hints at the eruption's size.

With 38 cores taken from the seabed around both these volcanic islands, Jacqueline has a lot of work to do. But she's hoping to be able to build a picture of the frequency, timing, and scale of previous eruptions. And, importantly, how widespread the effects were.

Her work will feed into the wider Beneath the Waves programme - a five-year research project led by GNS Science to investigate these two nearshore island volcanoes.

The anatomy of a volcano

The overall goal of the programme is to identify the full extent of the risks these active island volcanoes might pose to mainland communities.

Could they trigger tsunamis that would impact the coastline? Might ash make it across the ocean buffer and cause air quality and soil problems? And at what frequency might eruptions of this scale occur?

One aspect of the project has been to map the anatomy of the two volcanoes.

Using sensors that can detect changes in the conductivity of the rocks in the crust, the researchers are able to reconstruct a 3D map of the pluming of the volcanoes - where the magma chambers, and hydrothermal systems (the paths that water heated by the magma takes) are. GNS Science geophysicist Dr Craig Miller hopes this will give context to future monitoring and help them better interpret any signals they see.

This mapping will also enable them to look for any spots in the seabed floor weakened by volcanic activity that might have the potential to slide and cause a tsunami when an eruption occurs.

Listen as Craig explains to Claire Concannon the differences between the two volcanoes, and how the team hopes this research will help with hazard mitigation. …

Go to this episode on rnz.co.nz for more details