Scientists estimate Mt Taranaki has a 50 per cent chance of erupting within the next 50 years. Photo / Alan Gibson
What would it be like to live in the shadow of a constantly-erupting Mt Taranaki? Scientists are about to give us an idea, writes Jamie Morton.
To your typical Taranakian, the 2500m-high stratovolcano that dominates the region is what it always has been: a dramatic but docile feature of the skyline.
A place to go sledding in winter and tramping in summer, or a stunning backdrop for dairy paddocks and social media snaps on blue-sky mornings.
It might surprise them that their local mountain is considered by scientists as the most likely volcano to cause national-scale impacts in their lifetime, with the chance of an eruption probability sitting at around 50 per cent in the next 50 years.
That should be a big concern for the more than 85,000 people live within 30km of the mountain - 40,000 of who are in high-priority evacuation areas.
Auckland University volcanologist Professor Shane Cronin suspected it wasn't.
"Volcanic hazards are like many other natural hazards in being seen as either too big to cope with or too far off to worry about," he told the Herald.
"When pressed, people normally think that the only response is to run away, with thoughts of a doomsday scenario."
By contrast, eruptions and ash falls play out each year, month or even day in many parts of the world - think Indonesia and Mexico - so much so that they become part of life.
This prompted Cronin and his colleagues to consider Taranaki.
Two decades of chipping away at the understanding of eruption histories and probabilities had helped them realise that it had a split personality akin to Dr Jekyll and Mr Hyde.
For centuries, it might lay silently, like it has done since its last big bang in 1790.
But once it woke, it might begin erupting semi-continuously for years, decades or even centuries.
We know from the past 30,000 years of Taranaki eruptions that these mostly occur in clusters, with very few isolated events present in the geological record.
Over the past 3000 years, there had been about seven periods where tens to hundreds of individual eruption events took place, but only perhaps a few that were one-offs.
In one period, about 2000 years ago, there were at least 11 extremely large ash-producing events that deposited ash across large areas of the North Island.
The most recent eruption period was the "Maero eruptive period", which lasted between 1000 and 1790.
This saw a dozen large eruptions that built up the present Northwestern flanks of the volcano.
"We see also evidence for more than 20 ash-producing events during this time that dusted the surrounding landscape, and further events that were on other parts of the volcano, including river valleys to the south, west, east and north," Cronin said.
"That is to say, for about 800 years, there were eruptions happening every few years at the least."
Scientists were also aware that many other smaller eruptions - if you consider something the scale of the 1995-96 events at Ruapehu small - happened but weren't big enough to register on the record.
Nonetheless, they were still strong enough to disrupt air-traffic, electricity distribution, and pose major local consequences for waterways and soils.
What did that mean for a region that remains an agricultural and energy powerhouse?
A recent estimate of the net losses in economic activity from a brief Taranaki eruption was crudely estimated at between $1.7b and $4b – or between $13 billion and $26b over a decade of volcanism.
"It doesn't mean running away and never looking back to Taranaki, because most of the eruptions will affect only localised areas, places where targeted evacuations can save lives," Cronin said.
"What the eruptions will do, however, is cause massive disruption to our ways of life."
Not only would the disruption come through physical impacts like blankets of ash, surging lahars or potentially deadly pyroclastic flows, but also through fear and uncertainty.
"How would you as a farmer, business owner, whanau on traditional land or a private individual think about an eruption sequence that lasted for a year?" Cronin said.
"Probably, buckle down and grit it out, or if you were mobile, go and seek a job in another region. What if it was three years, or 10 years or 100? This is when we need to think about how we could adapt.
"The same could be said for Auckland Airport: down wind from most eruptions of Mt Taranaki, what would business plans look like if daily ash-forecasts were part of the mix of operating?"
Adaptation was thus the big reason Cronin proposed a major five-year study just awarded a $13.7m grant through the Government's Endeavour Fund.
"We felt that knowledge of how New Zealand could adapt under situations of extreme natural hazard uncertainty were missing," he said.
"We are good at event response, less good at recovery and probably not really tested in a case requiring true adaptation."
Taking a case where a change in the hazard state of a region went from a zero state to high alert would prove a major test for the nation.
"The Canterbury Earthquake sequence showed us just how hard it is to recover from a series of events. What if there were a scenario, like the Mt. Taranaki scenario, where the volcano started, and essentially, never stopped?"
In the new programme, which Cronin is leading with economist Dr Garry McDonald of Market Economics, the research team aimed to shed some more light on what the response might have to look like.
"How do we manage far-field impacts on our airports, electricity supplies, tourism. Are our business practices and farming methods going to work? What can we do to adapt.
"And adapt we must, because in such long-term hazard scenarios, there is no going back to normal."
At the hard science end of the project, the team will be using new tools to probe deep into the roots of the volcano so that we can understand how the wider system worked.
"We know at a basic level, but new scientific tools and techniques, and new overseas knowledge can help us to paint a much clearer picture of how the magma system works, not only to examine when something new might happen, but more importantly provide us the tools to understand what goes on during long lived eruptions," he said.
"These will pave the way for detailed operational scenarios of how eruptions could impact on the daily lives of people, businesses, iwi-hapu and communities."
One recent study found that a pyroclastic flow from Taranaki could spread further than first thought, with serious implications for populated areas within the danger zones.
Its new estimates put many Taranaki towns at risk, although the main areas of New Plymouth were protected by the edifice of the older Pouakai volcano.
The new project takes a much wider scope, bringing together researchers and scientists across a range of institutions, along with national and regional authorities, airports, electricity distributors and major industries.
"With these groups we will be exploring their options and thinking about adaptation around extreme scenarios of long eruptions," Cronin said.
"We'll be seeking their information needs so that we can provide the right kind of new data and explanation for them."
There would be a special focus on Matauranga-a-Iwi, or traditional Maori knowledge of volcanic history, alongside an adaptation scenario tailored for iwi.
Cronin said the ultimate result would be a toolkit that helped anyone weigh up the consequences of hazard mitigation and adaptation plans against cost and consequences, across scale and time.
"Currently, we have only a limited ability to test out how society and our economies might transition successfully through ongoing disruption events," he said.
"We can live through a long lived volcanic eruption, and other major natural hazard changes that are semi-permanent.
"We just have to learn better how to adapt to states of ongoing disruption.
"With this research we will bridge the gaps between uncertainty about a major likely hazard to face New Zealand, that is not catastrophic, but likely to be hugely impactful through time to the Taranaki region and rest of New Zealand."
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