Volcanic tremor levels at Mt Ruapehu are among the highest GNS has seen over the past nine years.
Its volcanic alert level was raised to two in March to reflect "moderate to heightened" unrest and the "potential for eruption hazards".
GNS volcanologist Yannik Behr said that over the past eight days, the temperature at Mt Ruapehu's Crater Lake (Te Wai ā-moe) has risen further from 32C to 36C.
"Volcanic tremor levels remain elevated and, after a slight increase over the past week, are now amongst the highest levels we have seen over the past nine years," he said.
"Crater Lake water and gas sampling and an airborne gas flight were completed last week. Analysis of the lake water and gas samples do not indicate significant changes in the geothermal system feeding into the lake."
Behr said the amount of gas released through the lake has increased from earlier measurements, but it is still within the typically-observed long-term trends.
The crater lake has also changed to a battleship grey colour as upwelling waters have disturbed sediments on the lake floor.
"The results to date are typical for the beginning of a heating cycle with the exception that tremor values are unusually high," Behr said.
"Current data indicate that normal processes seen at the crater lake are occurring. Gas and fluids from the shallow magma under the volcano are interacting with the crater lake geothermal system, causing heating of the lake, volcanic tremor, and increases in gas emission at the surface."
He said this activity at Mt Ruapehu is consistent with elevated volcanic unrest, so the volcanic alert level remains at level 2 and the aviation colour code remains at yellow.
Behr added that Mt Ruapehu is an active volcano that could erupt with little to no warning when it's in a state of elevated volcanic unrest. And at level 2, eruptions are more likely than at level 1.
"Volcanic alert level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity," he said.
"While volcano alert level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning."
GNS and its National Geohazards Monitoring Centre will continue to closely monitor Mt Ruapehu for further changes.
