Mt Taranaki eruption could knock out power to entire region

The view of Mt Taranaki reflected in the tarns on the Pouakai saddle. Photo / RNZ

By Robin Martin of RNZ

Contrary to popular opinion, Mt Taranaki is neither extinct or dormant, but an active volcano with a 50 per cent chance of erupting in the next 50 years.

New modelling has revealed a significant eruption could knock out power to the entire region.

Mt Taranaki is believed to last have erupted more than 200 years ago.

University of Canterbury professor in disaster risk and resilience Tom Wilson reckons the next time it erupts it could be severe.

"Given that the last eruption was, we think, back in the 1700s about 1760-ish, it possibly means there's been a recharge of the magma chamber and the next eruption is going to be a little bit bigger or on the bigger side of what Taranaki can produce," Wilson said.

Wilson has been working with PhD student Alana Weir to examine the risks posed to the region as part of a study called Transitioning Taranaki to a Volcanic Future.

It is focused on the disruption to the economy, infrastructure and the road to recovery after an eruption.

Wilson admitted the combination of a large ash cloud and damp conditions kept him awake at night.

Taranaki's prevailing westerly winds meant that spelt trouble for the region's single connection to the national power grid at Stratford, he said.

"If it's sort of misty rain or just damp, it can wet that ash and then it becomes extremely electrically conductive and what that can lead to is a great big short circuit.

"It's called a flashover where the insulators are contaminated and they lose their ability to insulate or have a reduced ability, and so it could disrupt electricity supply for Taranaki."

There was no workaround if the Stratford grid exit point failed and other lifeline infrastructure would soon begin to fall over without power, Wilson said.

Taranaki Civil Defence regional manager Craig Campbell-Smart said there was there was a good understanding of the immediate threats to life during an eruption such as falling rocks, deadly pyroclastic flows volcanic mudflows or lahars and the study had brought into focus secondary hazards.

He was also worried about electricity supply.

"That's the key lifeline asset for us that could be taken out by an accumulation of ash fall and so that's a really important work to focus on building resilience into that asset, and the asset owner Transpower and the lines company Powerco I'm sure will be looking to invest more strongly into the future but also to understand the vulnerability that they have at the moment."

Campbell-Smart said the region's drinking and waste water would be compromised without power as would the ability of oil and gas facilities to operate.

What does the public know?

On the streets of New Plymouth there was mixed understanding of how likely an eruption on Mt Taranaki was.

Joe reckoned any threat was a while off.

"I've heard it has a major eruption once every hundred thousand years or something like that."

Helen was expecting anything untoward.

"We were told it was dormant at school, yeah, we were told it was dormant growing up."

Blair had heard something similar.

"I thought the mountain was asleep but could wake up at anytime."

Leah was closer.

"It's overdue already so we're just waiting for it to happen."

Dale hit the nail on the head.

"I believe it's active ... maybe in the next 50 years."

Campbell-Smart reckoned it would take some work to bring the public up to speed on the real threat the volcano posed.

"The length of time from the last eruption is long and we've just lived and grown up in this region without experiencing those eruptive events so that's quite a bit of history to re-tell and that's a challenge, but I think it is a really important one."

He wanted everyone to do their bit by making sure they had three days' drinking water and a week's worth of food at home so they could care for their own immediate needs in the case of an eruption.

In a statement, Transpower said all its overhead electrical networks - both transmission and distribution - were susceptible to volcanic activity.

The state-owned enterprise said although there was no specific workaround that would guarantee supply to Taranaki in the case of an eruption, it did have diversity of supply to the region with transmission lines coming from both the north and south.

Transpower said it continued to work with researchers - including those at GNS and the University of Canterbury - to monitor and understand changes to probability or consequence models across all hazards that could impact the its network.