Continued strong tremors and high levels of volcanic gas emissions at Mt Ruapehu may cause dangerous volcanic mudflows within only a matter of weeks, GNS Science says.
Mt Ruapehu has seen heightened unrest for nearly two months and the past 12 days have seen the crater lake's temperature peak at 41C, after a four-week period of temperatures between 36 and 38C.
The volcanic alert level remains raised at level 2, which reflects "volcanic unrest hazards" and the "potential for eruption hazards".
GNS Science duty volcanologist Brad Scott said Mt Ruapehu was likely to see "minor eruptive activity that is confined to the lake basin" within the next month.
"This level of activity may generate lahars (dangerous volcanic mudflows) in the Whangaehu River."
An eruption larger in scale was also possible, Scott said.
"The next most likely scenario is a larger eruption that impacts the summit plateau with volcanic surges and generates lahars in multiple catchments, like what was seen after the September 2007 eruption or older events like those in 1975 and 1969.
"An eruption of this size would cause life-threatening hazards on the summit plateau and in valleys impacted by lahars.
"The chance of a prolonged eruptive episode or a larger eruption, such as occurred in 1995-96 with wider ashfall impacts is higher than it was two months ago but within the next four weeks remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions."
Scott said the continued unrest had caused strong volcanic tremors at Mt Ruapehu since early March.
GNS and the National Geohazards Monitoring Centre would continue watching Mt Ruapehu closely for further changes, he said.
