Mt Taranaki has erupted more recently than experts previously believed, it has been revealed.
Massey University vulcanologist Shane Cronin told the annual Taranaki seismic and volcanic hazards advisory group meeting last week that the mountain's last eruption was not the 1755 Tahurangi ash eruption.
"Now we can show that at least one further eruption occurred after Tahurangi ash, producing hot-pyroclastic flows down the northeast volcano flanks [in the Maero Stream to Pyramid area]," Prof Cronin said.
"We cannot place a definite age on the latest eruption [tentatively called the Pyramid eruption], because it is too young for radiocarbon dating.
"However, through soil accumulation, we know that it could have been any time up to around AD1800."
Prof Cronin said a study of long-term erosion rates and processes in the upper Stoney River catchment had been undertaken with Landcare Research Ltd.
"This has revealed a high potential for ongoing erosion of this nature and also highlighted the lack of precise topographic information available for Mt Taranaki," he said.
In December last year, millions of tonnes of rocks and sand collapsed on the western side of the mountain near the headwaters of the Stoney River.
Prof Cronin said during the next year a plan would be developed to install three or four continuous GPS receivers around the volcano to examine over a three- to five-year period whether there was any expansion, sagging or tilt of the volcano associated with potential early signs of collapse.
Good news to come out of the meeting was that the mountain will not blow its top before New Year's Eve but after that it's anyone's guess. GNS Science reported seismicity in Taranaki, between July 2010 and June 2011, had continued to be about the average during the past 15 years, with 286 earthquakes recorded.
"Only a few of which were felt by anyone and none of which were damaging and only one under the mountain," Taranaki Regional Council environment quality director Gary Bedford said.
"So we've got no signs of magma movement and we have a guaranteed two to three months before the mountain might blow up, but who knows after that."
Any movement would evolve relatively slowly. "We are probably talking weeks or months before anything bursts out of the surface." Mr Bedford said the council would be advising key groups, including farmers, and water, gas and electricity suppliers of the meeting's conclusions.
- © Fairfax NZ News
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