Ash and dark plumes can be seen coming from Whakaari/White Island for the first time this year - showing a greater level of unrest at the surface of the volcano.
As a result, GNS said in a statement today it had raised the volcanic alert level to level 2 and the Aviation Colour Code to Yellow.
Volcanic alert level 2 indicates the primary hazards are those expected during volcanic
unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity.
While volcanic alert level 2 is mostly associated with environmental hazards,
eruptions can still occur with little or no warning.
After a severe wet weather stint, scientists completed a gas monitoring and
observation flight over Whakaari/White Island yesterday, the statement said.
Some occasional "deposits" had been observed on some of the island's webcams, and a darker-than-usual plume was also reported at times.
Monitoring during a flight confirmed the presence of some ash in the plume, which came from the main steam vent at the back of the crater lake.
Initial analyses of the ash particles suggest it is loose material from around the vent or underlying conduit being carried by the steam and gas emission.
While the gas output observed on Thursday was higher than recent observations, other monitoring parameters did not show significant changes, GNS said in the statement.
The status is now raised to level 2 after observations of vent activity and monitoring data.
Observations from the flight show there is no substantial change in the location and size
of active vents.
The rainfall formed a pool of water on the floor of the 1978/90 crater, reforming a shallow lakelet.
During the past week, a small sequence of earthquakes has been located close to the volcano and there were several episodes of slightly increased volcanic tremor.
None of these were unusual for Whakaari/White Island and it remained unclear whether these were just coincidental with the incorporation of material in the plume, GNS said.
During fine weather, moderate to large gas-steam plumes will be seen rising above the island and trailing off downwind.
Some particles may be carried a few kilometres downwind, but are unlikely to reach the mainland.
In the statement, GNS said should any explosion produce a significant ash cloud, the likelihood of ash affecting the mainland was still very low. The gas and steam plume might be noticed on the mainland as weak acid rain.
Changes at the vent resulting in the minor ash emissions have not been seen at
Whakaari/White Island this year and show a greater level of unrest at the surface.
There are no indications currently of a substantial change in the overall behaviour of the
The main plausible triggers for a sudden eruption with little or no warning are still the collapse of unstable material in an active vent and the possible ingress of water underground onto the shallow magma body.
Whakatāne mayor Judy Turner said this was the first she had heard about the unrest and change to the alert level, but said she trusted if there was a concern for the public she would have been notified.
Local resident David Marshall lived in view of the volcano and said he has not seen any unusual activity from the volcano.