Volcanic ash impacts more frequent in Auckland scientists find - 11/10/2010

Scientists have identified 29 previously unknown volcanic ash layers while drilling into ancient eruption craters in Auckland. Some ash layers have come from eruptions in the Auckland area, and others have come from volcanoes in the central North Island and Taranaki.


Rangitoto Island, in Auckland's Hauraki Gulf, is the youngest and largest volcanic cone in Auckland. The Auckland Volcanic Field produces single-episode eruptions and the location of the next eruption is not known. Photo: Lloyd Homer, GNS Science

The new findings mean Auckland may be more vulnerable to ash-fall from volcanic eruptions than previously thought.

On average, the Auckland isthmus has been impacted by ash-fall from local or distant eruptions once every 400 years for the past 80,000 years. The previous estimate was once every 750 years.

The insights, released to coincide with the screening of a TV3 docu-drama about an eruption in central Auckland, have come from a multi-year research project aimed at improving the understanding of the hazards posed by the Auckland Volcanic Field.

Present understanding of the Field and its behaviour is incomplete and the project, called DEVORA or Determining Volcanic Risk in Auckland, is filling in the knowledge gaps.

The project started in 2008 and is jointly led by GNS Science and The University of Auckland.

Under the DEVORA project scientists have been systematically addressing information gaps in three themes – geological understanding, probabilistic hazard, and risk and social aspects.

In the geological theme, the researchers are studying the magma body under Auckland to better understand how rapidly it might rise to the surface and what pathways it could potentially take.

Under the probabilistic theme, the researchers are refining the eruption ages of Auckland’s 49 volcanoes to improve the overall understanding of the eruption hazard.

It was while studying drill cores from eruption craters and lakes that the science team discovered 29 previously unrecognised volcanic ash layers. The layers not only pinpoint an eruption date but, in some cases, they also indicate the size and source of an eruption.

In the risk and social theme, the researchers will bring together the improved understanding of the Field and turn it into mitigation measures that can be implemented by a range of organisations.

In another research project, being led by Massey University, information from the drill cores has been used to build a statistical model giving likelihoods of the locations and timing of future eruptions. The project is called Facing the Challenge of Auckland’s Volcanism.

In a third more specifically focused project, highly sensitive seismometers have been installed at various depths in a 380m-deep borehole under the refurbished south stand at Eden Park.

The project, called Borehole Instrument Centre for Eden Park – BICEP, is being led by the Institute of Earth Science and Engineering at The University of Auckland.

Its aim is to develop a better understanding of earthquake activity under Auckland, and the way the different rock layers and engineered structures respond to earthquakes.

In addition, analysis of the rocks and soils removed during the drilling process has added to the understanding of Auckland’s geological history.

At the base of the borehole, noise from industrial activities in the city is reduced allowing small earthquakes to be measured more precisely.

Taking seismic recordings at a range of depths enables scientists to track the movement of seismic waves from the bottom of the borehole to the surface.

As well as gaining a better understanding of Auckland’s earthquake activity, information from the borehole will also help inform engineering requirements for future construction projects in Auckland.

Volcanologist Dr Jan Lindsay, from The University of Auckland, said scientists were integrating research projects from institutes across New Zealand to increase the understanding of the volcanic threat that Auckland faced in the future.

The Auckland Volcanic Field covers 360sq km and stretches from Manurewa in the south to Takapuna in the north. It has been active for at least 200,000 years and, based on similar fields in other parts of the world, researchers believe it may have a life expectancy in excess of 500,000 years.