By Sarah-Jane O'Connor 14/12/2015

Tracking the source of volcanic ash has given a New Zealand researcher a better understanding of Auckland volcanoes and when they erupted.

Jenni Hopkins reconstructed the volcanic history of Auckland as part of her PhD research at Victoria University in the hope of better understanding the risk posed by new eruptions in our biggest city.

Auckland’s volcanic field is made up of over 50 craters spanning about 200,000 years of volcanic activity. Though currently dormant, the volcanic field is expected to erupt again from a new site within the next few hundred years.

Auckland’s 53 volcanoes are “monogenic”, Hopkins said, which means they generally erupt only once.

“But what was previously unknown was the order in which they erupted – I wanted to find that out so that we could establish the characteristics of the field and get an idea of what a future eruption might be like.”

Hopkins used lake sediment core samples drilled by GNS Science and Auckland Council’s research programme DEVORA (DEtermining VOlcanic Risk in Auckland) and searched for ash deposits. The thickness and order of the ash layers helped reconstruct the eruptive history of the area.

She also developed a new technique which, for the first time, allowed the ash samples to be accurately linked back to the volcano that produced them. The elemental make-up of the ash deposits had unique geochemical “fingerprints” of trace elements which matched the lava from source volcanoes.

“Being able to pinpoint the volcano from which each layer of ash was derived means we can see how far ash was dispersed in each eruption,” Hopkins said. “We can use this geological evidence to make estimates about the areas that will be affected by eruptions in the future.”

“The whole point of my work is to provide an improved understanding of the threat posed by Auckland’s volcanoes to both people and critical infrastructure. It’s designed to assist in the development of better management practices for evacuations, and to help local authorities work out how best to mitigate the damage to assets like roads, power lines and buildings.”

Hopkins’ research was funded by the Earthquake Commission, DEVORA and GNS Science. She is now working for GNS Science and would like to apply the techniques she used in Auckland to study the ancient super-eruption of Taupo by examining its far-flung ash deposits.


Featured image: Flickr CC, Auckland from Mt Eden, Robin Ducker.