Frank Greenall: Keep Auckland's port, move the city

COMMENT

Whakaari/White Island tragically reiterated how conditions can quickly turn pear-shaped around things volcanic.

Yet, our largest city sits plum atop a hornets' nest of volcanoes - all 50-plus of them. True, they're classified as dormant, but the trouble with dormancy is that – like Dr Frankenstein's monster – it can burst into life at any moment.

Rangitoto (blood-red sky) was the last Tamaki Makaurau eruption, about five or six centuries ago. But that's a gnat's blink in geological time.

Common sense would say, forget the port – best haul ass outta there before Vulcan wakes up and hammers Auckland property values once and for all.

Author Bill Bryson covers a lot of territory – both literally with his travel writings, and more generally with an enquiring mind that covers nearly everything under the sun. Hence his cracking book: A Short History of Nearly Everything.

In it, Bill tells an amusing - yet frightening – story of how back in the 1960s a curious geologist was puzzled why he couldn't find the caldera of USA's Yellowstone National Park despite diligently traipsing all over its huge precincts.

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Yellowstone is one helluva volcanic hotspot – containing more geysers than the rest of the world's active thermal regions combined. Unlike the cone-forming Mt Taranaki-type volcanoes, calderas are depressions left when explosive ruptures blast open what used to be the underground magma, or molten lava, chambers.

It was only when Nasa coincidentally dropped off some very, very high altitude photos of the park that the geologist realised virtually the whole park – all roughly 9000km 2 of it – was in fact the caldera itself. It's still the world's biggest active volcano.

Calculations showed the last major eruption that created the present "Park" was about a thousand times larger than the epic 1980 Mount St Helens eruption in Washington State, which itself was equivalent to 500 Hiroshima-sized atomic bombs.

The fallout was such it covered parts of Nebraska – 1600 kms away - in three metres of toxic ash. Some of this even reached as far as New Zealand in the form of that gritty stuff in the early versions of the mighty Ajax bath scourer. They initially mined and used it without having a clue as to its origin.

Today, Yellowstone still fizzes, smokes and belches all sorts of toxic emissions, but it doesn't stop about three million visitors annually flocking to the place to get a taste of hellfire and brimstone.

Think White Island, but about 10,000 times bigger. And just like Whakaari, it could blow again at any minute.

The good news is that the geological record shows that a major eruption in the Yellowstone region occurs on average only about once every 600,000 years.

The bad news is that the last time the balloon went up was about 630,000 years ago. It's overdue. And on the last occasion, the ash fallout blanketed just about all of the USA west of the Mississippi – an area that now produces about half of the world's cereal grains, and homes a few hundred million homo sapiens.

Just down the road from Auckland, there's heaps of previous volcanic form, although part of a different volcanic field. The 1886 Mt Tarawera eruption – which destroyed the Pink and the White Terraces (they were two separate terraces) - occurred, in geological terms, just yesterday.

A bit farther on is the legacy of the mother of all local eruptions – the huge water-filled caldera today known as Lake Taupō. One of the biggest volcanic events in the planet's history, it still holds the record for the widest known distribution of volcanic ejecta.

Should visits to Whakaari now be banned? The central plateau's volcanic hotspots swarm with tourists and winter sports fans – many more than at White island. Fence those off, too?

The reality is, Aotearoa's long white cloud could at any minute turn into a massive volcanic ash cloud. We're all cats on a hot thin roof.

•Frank Greenall is a Whanganui-based freelance writer and columnist.