Saturday, 5 May 2007

Bets Mt Taranaki blowing top in 50 years

IF betting agencies took punts on natural disasters, you’d be wise to put your money on New Zealand's Mt Taranaki blowing its top in the next 50 years.
You might not be around to collect the winnings, but your descendants would be toasting your foresight with an expensive bottle of champers, probably far from the poison ash fallout. Perhaps Paris.
Massey University scientists have fresh evidence the Egmont Volcano, as it’s known in geological terms, may have a history of violence even worse than previously thought.
So bad, that if it continues its destructive track record, there’s 50-50 chance it will act up before 2057.
Associate professor in statistics Mark Bebbington (left) has been calculating the odds based on a five-metre-deep core sample taken from Lake Umutekai, south-east of New Plymouth in New Zealand's North Island.
Imagine the sample as a standing pole with a series of horizontal stripes made up of alternating layers of ash and soil.
The ash tells the scientists when an eruption occurred and the soil in-between shows them how much time passed between volcanic events. The longest lull appears to be 450 years, while the shortest span is placed at 10 years.
Dr Bebbington says the ash at the bottom has been dated at 10,000 years old, while the top layer is just 1500 years old. The sample shows there have been 104 events in those 8500 years. But scientists know the mountain’s last blast was in 1854.
Unlike Split Enz, geologists and statisticians believe history does in fact repeat.
“Basically, volcanoes are recurrent systems,” Dr Bebbington says.
“The wild card is that we are saying that the past is the best model for the future.”
With that in mind, it appears Mt Taranaki could be in another long sleeping spell.
But then again scientists believed Mt St Helens was an extinct volcano. In 1980, the mountain proved, catastrophically, how wrong those experts were.
Not Massey’s mountain specialists. They know the 2518-metre-high cone is just biding its time to vent.
After examining the figures and working out a distribution system on that one core sample, Bebbington says there is a 33-50% chance of Taranaki becoming active in the next half-century. “That’s fairly conservative,” he says of the estimate.
That’s because there’s more. In fact, another core, this sample taken last year from Lake Rotokare, south-east of the mountain near Eltham.
“It appears there were quite a number of events in that sample that don’t correspond with the one from Lake Umutekai,” he says. What this means is that the chance of an eruption just rose – along with the eruption count from days gone by.
“My gut feeling is that there have been somewhere between 150 and 200 (volcanic) events,” Bebbington says of that 10,000-year period.
While the new numbers don’t go back as far as the 450-year slumber period, the ash deposits show that wind direction has a lot to do with reading the life-lines of volcanoes.
In other words, if the wind was blowing a different way during the volcanic explosion, the ash may have landed somewhere else.
The discrepancies between the two core samples show this.
But Bebbington says scientists are still trying to match up the geochemistry of the ash samples, so a final reading on the mountain’s fiery future is yet to be revealed.
Just know, there are sensitive seismic recorders all over the rising landmark, which is being (thankfully) stubbornly still.
There is movement though. “East off the end of Taranaki there’s some activity there,” Bebbington says.
These deep-earth rumbles may be a sign, a hint from down-under, that the sleeper is about to awake.

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