What would happen if an Auckland volcano erupted

8:50 am on 6 March 2017

The biggest danger from a volcanic eruption in Auckland would be a pyroclastic surge - a hot mix of gas, ash and other substances - that would spread over a 5km-wide area, scientists say.

A volcano erupting, with an ash cloud exploding into the air.

Photo: AFP / Mint Images

Over the last 190,000 years, there have been 55 eruptions in the Auckland Volcanic Field which covers an area of 360 sq km.

A team of researchers, including experts from GNS Science, Canterbury University and Massey University, has been looking into how some of Auckland's critical infrastructure would hold up if another eruption occurred.

Their work is the first complete eruption scenario developed for Auckland since the 1990s.

The researchers looked at a hypothetical two-month period beginning with the first signs of activity through to an eruption and the emergence of a new volcano near Mangere Bridge.

Tom Wilson, associate professor in disaster risk and resilience at the University of Canterbury, said there would be "near total destruction" within 2km of an eruption vent from the pyroclastic surge.

Houses, buildings and critical infrastructure within that area would be destroyed but structures 4km to 5km out could withstand the eruption, he said.

Dr Wilson said disruption to services like electricity, water, communications and transport could go on for a long time, depending on where the eruption happened.

"Many of the key infrastructure networks are channelled in between the two harbours and there's a really dense area with lots of electricity and roading and water supply infrastructure.

"If they're impacted that could lead to service outages in some suburbs for potentially months or possibly even years after an eruption."

Dr Wilson said no-one knows where or when the next eruption would happen.

Comprehensive volcanic monitoring systems in place in Auckland would give some warning of an eruption - though that would vary from as little as a few hours, to as long as a couple of weeks, he said.

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