The volcanic alert level on Whakaari/White Island has been raised to two, with small amounts of volcanic ash being detected in the steam and gas plume.
GNS Science says volcanologists were able to carry out a gas monitoring and observation flight on Thursday, after a period of severe wet weather.
A darker than usual plume had been seen from the mainland and observations on the flight confirmed the presence of ash.
Those fine particles originate from the main steam vent at the back of the crater lake.
GNS Science said initial analyses of the ash particles suggested it was loose material from around the vent or underlying conduit being carried by the steam and gas emission.
"While the gas output observed on Thursday is higher than recent observations, other monitoring parameters do not show significant changes," GNS Science said.
During the past week, a small sequence of earthquakes has been located close to the volcano and there have been several episodes of slightly increased volcanic termor.
GNS Science said none of the observations are unusual for Whakaari and it remains unclear whether these are just coincidental with the incorpoation of material in the plume.
The island volcano erupted on 9 December last year, leaving 21 people dead either on the day or in the weeks following.
Two bodies have never been recovered from the island. Another 26 were injured, most with long roads to recovery.