Where is the least shaky place in New Zealand?

“Sometimes it does us a power of good to remind ourselves that we live on two volcanic rocks where two tectonic plates meet, in a somewhat lonely stretch of windswept ocean just above the Roaring Forties. If you want drama – you’ve come to the right place” — Sir Geoffrey Palmer

Move to Hamilton, GNS vulcanologist Graham Leonard suggests.

Nestled inland, Hamilton, population 130,000, is his pick for the most geologically sound city in New Zealand. It’s tucked away from the coast – cancelling out any risk of tsunamis – and is a safe distance from known fault lines. If Mt Ruapehu erupts, the volcanic ash is likely to be blown east across the island, and it’s far enough away from Auckland’s volcanic field to be considered safe.

Even if the Waikato River flooded, it’s in a deep enough riverbed that the city is unlikely to be affected, he says.

But if we’re talking specifically about volcanoes, Dr Leonard’s area of research, the whole of the South Island is pretty safe, with New Zealand’s prevailing westerly winds extremely unlikely to send any ash from a North Island eruption across Cook Strait.

Unfortunately, if you live in the North Island, there’s really no escape – especially if you live in the volcanic hotspots of the central plateau and Auckland.

If Mt Taranaki, Ruapehu, Tongariro or Ngauruhoe blew its top, clouds of ash would billow across the central and upper North Island, jamming wastewater treatment plants, overheating air conditioning units, and taking out electricity and air travel.

“It’s not toxic, but it is disruptive. The biggest [cause of] injuries during ashfalls is people falling off their roof, trying to get the ash off,” Dr Leonard says.

The real danger zone for flying rocks and hot ash clouds is in the immediate vicinity of these volcanoes, which are, luckily, rimmed by Egmont National Park and Tongariro National Park. Trampers and skiers would have to keep an eye out, and following eruptions there would be mass damage as the lahar flows of mud and rocks carved a path to the coast. Contrary to every disaster movie you’ve ever seen, molten lava moves so slowly you could easily outrun the sludge.

Lakes Taupo and Rotorua are part of a cluster of “caldera volcanoes” in the central North Island, the biggest of which, like Taupo, are known as supervolcanoes.

The carnage if one of these blew again doesn’t even bear thinking about – Lake Taupo used to be flat land till molten rock pulsed up from the ground, throwing 1000 cubic kilometres of debris around and leaving a massive hole that eventually became the lake. Happily, there were only tuataras around to witness this one-in-50,000-year event.

Sorry Auckland, but precariously nestled on a field of 50 active volcanoes, you could be considered a ticking time bomb. An explosive mix of two types of volcano – maar craters and scoria cones – are peppered beneath the city. The last one to explode was Rangitoto Island, about 600 years ago, so the chances of us seeing an eruption in our lifetime are very, very slim. “But you can’t rule it out,” Dr Leonard says.

The Bay of Islands through Whangarei is also a risk zone, with 60 volcanoes at the last count.

AT THIS point, you could be thinking about packing up and making for the east coast, or Wellington, or maybe the South Island. But wait, let’s factor in the Ring of Fire – the massive fault lines and hundreds of volcanoes that circle the pacific, pushed by tectonic plate collisions deep under the ocean. If one of those faults ruptured off of the east coast, tsunami would be likely to engulf the coastline. Live in a low-lying coastal area? Swamped. Even tsunami from the other side of the Pacific can be metres high in New Zealand.

And then, there’s the earthquakes.

New Zealand straddles the Australian and Pacific plates, with the major fault line carving a path from the east of the North Island right down to Fiordland in the south, GNS seismologist Mark Stirling explains. About 15,000 quakes are tracked a year, with 150 felt by humans.

But that’s not all. Off the east coast, the Pacific plate is trying to dive under the Australian plate. Down south, the Australian plate is trying to cosy up underneath the Pacific plate. If either of these “subduction faults” were to rupture, the results would be catastrophic.

In the North Island, a massive rumbling earthquake would be followed by a monster tsunami that would engulf Gisborne, Hawke’s Bay and Wellington, with waves of up to 30 metres washing about seven kilometres inland.

Wellington is widely considered New Zealand’s most hazardous city, with no fewer than four major surface faults in the region.

In its 2007 Hazardscape report, Civil Defence estimated a rupture of the Wellington fault would cause about 4000 casualties, up to 600 deaths (depending on the time of day), and more than $10 billion of damage. The fault produces a major earthquake every 500 to 800 years; it last ruptured about 400 years ago.

Nowhere in the South Island is quake- free, with the Alpine fault slashing through the west, and minor faults zig- zagging through central Otago, Queenstown, Dunedin and Christchurch. All up, GNS has mapped about 530 fault lines in the country – not including the sneaky little lines, or the offshore plates.

If you wanted to avoid any shakes at all, your best bet would be moving to the small settlement of Kaitaia, in Northland, according to Dr Stirling.

“That’s about as far away as you can get on dry land from faults, and areas of seismicity.”

Unfortunately though, Northland is at the mercy of New Zealand’s biggest and most expensive natural hazard – the weather. As a group of small islands in the Roaring Forties, weather patterns mean we experience a lot of high- intensity rainfall.

Humid, tropical cyclones bear down from the north, lashing the top half of the North Island. And though weather from the north brings more rain, Niwa meteorologist Mike Revell says nowhere in the country is safe from nasty mid- latitude storms, which can bring winds of up to 230 kilometres an hour.

On average, there are about 10 of these a year.

“There’s nowhere you could rule out the possibility of having something like that. They can affect us basically at any time of the year.

“They tend to peak in the winter, but there’s no guarantee they won’t hit us in the summer either.”

So pick your disaster to run away from, and then you either end up in the South Island, Hamilton or Kaitaia, as long as you don’t mind being exposed to the other natural disasters.

 

The Dominion Post

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