An eruption of Mt Ruapehu is inevitable but is unlikely to be imminent, says volcanologist Professor Shane Cronin.
There is continuing unease over recent volcanic activity on Mt Ruapehu, especially with the winter ski season about to begin.
Experts have said they don’t expect an eruption imminently but are urging people to be cautious.
The latest report from GNS Science says the elevated tremor levels on Mt Ruapehu have now been sustained for four weeks - the longest period recorded in the past 20 years.
However, the scientists say everything they have seen from an observation flight and sampling of the crater lake suggest this is a normal heating phase.
They believe the chance of a large eruption is higher than it was two months ago but remains very unlikely.
These thoughts are shared by Cronin, who thinks there is enough venting of gases currently to keep Mt Ruapehu stable.
It’s always a situation of how well that gas sealing takes place,” says Cronin.
“We could see a few more of these heating, cooling cycles. Eventually, it will explode.”
“We know Ruapehu erupts every 11 years on average, through our recorded history. So, it will erupt at some stage.”
Cronin has been carrying out research into the January eruption of Tonga’s Hunga-Tonga Hunga Ha’apai volcano and says there are some parallels between the two.
He told Breakfast that while Mt Ruapehu is a lot smaller than Hunga-Tonga Hunga Ha’apai, both operate with what he describes as a “pressure cooker” system.
“The lid of the pressure cooker is under Te Wai ā-moe, the crater lake,” says Cronin.
“That pressure cooker has to hold the pressure of the gases coming up underneath.
“If that lid is a little bit leaky, then the gases that come up underneath can vent out and we don’t build up an explosive pressure.
“But if that pressure cooker lid is sealed tight, then the gases build up underneath and an explosion occurs.”
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