A Matter Of When, Not If

The region has been given some sobering reminders of the need to be prepared for some particularly Taranaki Civil Defence emergencies.

A panel of experts this week (Thursday 21 September) told two New Plymouth seminars of the probability and consequences of volcanic activity on Mount Taranaki.

And while such forecasts can't be as precise as weather bulletins, experts believe that:

* There is a more than even chance of volcanic activity within the next 50 years. * Once this activity starts, it is likely to be prolonged - perhaps for years, on and off. * While a hugely explosive eruption is considered unlikely, the region can still expect considerable danger, damage and disruption from lava and mud flows, slope collapses and ash fallout.

The seminars - one for Civil Defence stakeholders and one for the public - included presentations by a number of expert advisers to the Taranaki Civil Defence Emergency Management Group. The experts' students also discussed their work in Taranaki.

According to Mark Bebbington, of Massey University, analysis of core samples from beneath Lakes Umutekai and Rotokare suggests there is a 52% chance of an eruption in the next 50 years. This is based on the core samples' geologic evidence of previous volcanic activity.

Taking a different tack and studying the chemistry of material from previous eruptions, student Michael Turner suggests volcanic activity on Mount Taranaki correlates with the replenishment of magma reservoirs 7km to 10km under the earth's surface. While his studies suggest we may be safe for the moment, the pattern is compelling.

Massey University Professor Vince Neall warns against simplistic scenarios. The region could well experience lots of large earthquakes, fallout from volcanic activity in the Central North Island and activity on Mount Taranaki all at the same time. "These things are all connected," he says.

Classifying volcanoes into two types - the spectacular, pumice-forming explosion that produces ash plumes tens of kilometres high; and the quieter "cone-forming" eruption that produces lava flows and slope slips or lahars - Shane Cronin of Massey suggests the latter is more likely than the former but is likely to last for some time - decades or longer, on or off.

In the meantime, he's not advising building homes in the river valleys of the region's ringplain.

He makes a comparison to the behaviour of currently active volcano Mt Merapi in Indonesia, described as a "twin" to Mt Taranaki. Merapi's current activity began in 1994 and has caused some 7,000 deaths and, at various times, the evacuation of hundreds of thousands of people.

So how much warning will we get? Brad Scott, of GNS Science, believes there may be a year or two of volcano-related seismic activity before it blows. "In the reactivation of the volcano, we'll see hundreds if not thousands of earthquakes generated."

So far, no earthquakes recorded or located in Taranaki have shown evidence of being related to underground movement of magma.

Ash fallout from any eruption will pose problems on many fronts, particularly water supplies. "It's good that you have lots of milk tankers here," says Prof Neall. "You might be needing them."

Even a relatively light dusting of ash may also pose big problems for electricity supply, according to Massey University's Ian Chapman. According to his studies, 1 mm of wet ash or 2 mm of dry ash is enough to cause flashovers and other problems. Ash is very conductive and "if it coats insulators, it prevents them being insulators".

Stock would also be affected by ash but studies by Canterbury University's Tom Wilson suggests moving them away would be difficult.

There is some precedent - 13,500 head of stock were evacuated during the 2004 Bay of Plenty floods - but greater numbers would be involved if Taranaki erupted.

Mr Wilson says, for example, that evacuating a zone north-east of the mountain would require some 208,000 head of stock being moved. This would take 37 to 92 days depending on the availability of stock trucks. A seven-day evacuation would need 264 stock trucks working round the clock.

So how do we prepare? Emergency Management Officer Des Paulsen's advice to the public seminar included:

*Following the Get Ready Get Thru advice in having a household emergency plan and emergency and getaway kits. See www.getthru.govt.nz .

* Considering location and house design (steep and strong roofing, enough height above mud flows) when buying a property. A map showing volcano evacuation zones is available on the Taranaki Regional Council website, www.trc.govt.nz , along with other useful information.

ENDS

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