Scientists have confirmed Ruapehu remains at a heightened level of unrest and that an eruption is "more likely than normal".
GNS Science head vulcanologist Gill Jolly said analysis was still showing higher than normal temperatures beneath the crater lake.
"We think this reflects a partially sealed zone a few hundred metres beneath the lake which might be causing a pressure build up behind it. That pressure would make an eruption more likely than normal.".
It doesn't mean that an eruption is inevitable, said Dr Jolly.
"If the sealed zone fails suddenly an eruption could occur, probably with little or no warning. If it fails more gradually then the pressure would probably be released more slowly and the likelihood of an eruption would revert to normal".
Eruptions in 1988, 2006, and 2007 are believed to have occurred as a result of sudden failure of a seal beneath the crater lake.
"We never have the whole story so there is always uncertainty in our assessment of what might happen at volcanoes. It's like detective work without all the clues. But when we see something that might increase the chance of an eruption we have to be more cautious", said Dr Jolly.
Small earthquakes 3 to 5 kilometres beneath the crater lake in late-October and early-November have now stopped. GeoNet said it was not clear if those earthquakes were related to the high temperatures estimated a few hundred metres beneath the lake.
The crater lake is quiet and its temperature has remained relatively low, 20 - 25 degrees Celsius, since March.
- © Fairfax NZ News
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