Fury of NZ's hottest island

By Jamie Morton, Alan Gibson

Our most active volcano is having a tantrum - and the experts don't know how long it will last. Jamie Morton and Alan Gibson explore White Island

Tourists make their way through the crater of the volcano on White Island. Photo / Alan Gibson
Tourists make their way through the crater of the volcano on White Island. Photo / Alan Gibson

Great craters spew plumes of blue and white high into the air and above 300m high walls are smeared sulphur-yellow and iron-red.

Across the alien moonscape everything is alive and furious - gas roars from the sides of hollow domes of rock, and the hot streams that have carved snaking ditches through the flats bubble and steam.

Chemicals hanging unseen in the air - up to 2000 tonnes of carbon dioxide and up to 800 tonnes of sulphur dioxide each day - invade the sinuses and dry the throat.

Welcome to Te Puia o Whakaari - New Zealand's largest volcanic structure and the barren, smoking island that Maori so appropriately named "The Dramatic Volcano".

As you approach it by sea, White Island cuts a harsh and jagged figure across the horizon, characteristically crowned by a column of bright white steam.

To the human eye, this 2km-wide, 321m-high, circular chunk of rock 48km off the coast of the Bay of Plenty is the volcano that sprang back into life last July and August, ending more than a decade of peace.

But like a monstrous iceberg, White Island is just the tip of a submarine mountain that rises a staggering 1.6km from the sea floor, its fiery innards sealed shut from the surrounding Pacific Ocean.

Over more than 150,000 years, the volcano has been building towards the sky, the magma chamber inside punching up like a fist and shooting off into fingers that form billowing vents at the surface.

The surface is transformed with every violent episode - what were once multiple large craters, or a huge lake once 90m deep, is now a rock-strewn field that can be traversed in a matter of minutes.

The field is enclosed by towering cliffs with great channels gouged by heavy rain running from the skyline to the floor below.

Remarkably, the silica content within these sheer structures of andesite rock measures at about 50 to 60 per cent - not far below the rhyolite rock found among the geology of volcanic areas with devastatingly explosive history, such as Taupo.

Within this hellish amphitheatre, White Island has performed the full gambit of volcanic drama - giant boulders hurled against its sides and into the sea, lahars from collapsed walls, ash vomited from its gaping vents and lava flows.

After an eruption in 2000, the ground was left so soft one could comfortably walk across the island in bare feet.

Despite its remote location, safely removed from the mainland, there have been casualties.

When the island was once mined for sulphur to make agricultural fertiliser, a devastating lahar swept through a campsite and killed all 10 workers, sparing only a cat named Peter by its rescuers.

Skeletons of concrete and iron are all that remain of a factory that ceased in the 1930s, after half a century of hard-fought efforts to reap boatloads of the pungent sulphur from the island.

Today, its sand is trod only by scientists, who arrive by helicopter for regular tests, and tourists - hundreds each week.

"It could be one of the great wonders of the world," said White Island Tours guide Hayden Inman.

"You get to walk right up close to a volcano - one of the most spectacular things mother nature has created.

"I've been out to the island more than 300 times and I still enjoy going out each day."

For scientists, tracking the volcano's behaviour has also been full of surprise twists, with activity swinging from relatively settled states to sudden ash eruptions.

The volatility has seen aviation alert levels raised from yellow to orange three times within a space of months.

What began with a series of quakes soon escalated into something scientists hadn't witnessed in New Zealand for a half a century.

In November, the volcano extruded lava - appearing on the surface as a black, craggy lava dome, plugging magma just below the surface.

A calm spell was broken again by a spate of seismic tremors.

What are called "hybrid" earthquakes - a quick jolt followed by a period of resonance - have presented a tell-tale symptom of rock fracturing and magma movement.

The lake had been the volcano's showpiece, its brilliant green waters coloured by bacteria that somehow found a way to survive in a chemical soup 50 times more acidic than battery acid.

But last Tuesday, the lake disappeared.

"It started to become more vigorous in late December and January, and since that time basically it has dried itself out but has cycled backwards a few times between dry and wet," GNS Science volcanologist Brad Scott said.

Remaining are two dry vents - the "August vent", which has chucked boulders up to 100m into the air and pumps out blue steam indicative of magma not far below, and the "January vent", which has sent mud flying 40m and fired off ash eruptions.

"The gas is a couple of hundred degrees hot and doesn't actually condense into steam until it's quite a long way above the vent."

GNS staff were restricting visits to the island because of the activity, its latest rattle a weak lunchtime ash eruption last Saturday.

"At the moment it's in kind of a status quo mode - there's enough activity to drive the unrest but it's never increasing or decreasing," Dr Scott said.

"What we are looking at from here is two primary scenarios - a, it stops, and b, it develops into stronger eruptive activity."

Which was more likely?

"Unfortunately, that's the question we can't answer, and it kind of reflects that state of volcanology."

A significant eruption would see rocks hurled about the crater or even into the surrounding sea, something that happened during nearly four decades of activity between 1976 and 2000.

But scientists are relatively comfortable the effects of an eruption would be limited to the island.

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