Whakaari/White Island may be heading into a new eruptive episode, GNS Science said.

It comes after the fifth anniversary of the deadly 2019 Whakaari/White Island eruption was marked in Whakatāne last week, with relatives of the 22 people killed among those attending commemorations.

GNS Science said in a statement on Monday the Bay of Plenty marine volcano had been observed producing larger steam and gas plumes, and occasional “passive” volcanic ash emissions.

“The volcano is not actively erupting but the current activity could be leading to a new eruptive episode,” duty volcanologist Agnes Mazot said.

The aviation colour code has been raised to orange and the volcanic alert level remains at 2.

The aviation colour code system is based on four colours and is only intended for use by the civil aviation community.

The levels are green – normal, non-eruptive state; yellow – signs of unrest; orange – heightened unrest with increased likelihood or eruption, or volcanic eruption is underway with no or minor ash emission. And finally – red – where eruption is forecasted to be imminent with significant emission of ash into the atmosphere likely, or eruption is underway with significant emission of ash.

“During a routine gas measurement flight on December 14, the emissions from the active vent changed and include more volcanic ash than when measurement started an hour earlier,” said Mazot.

“The results from the gas flight along with satellite observations, show a general increase in sulphur-dioxide (SO2) and carbon dioxide (CO2) emissions from the volcano.”

Mazot said these taken together indicate a new eruptive episode may be starting.

“During the gas measurement flight on 14 December, we observed minor volcanic ash emissions and an increase in gas emission rates,” Mazot said.

“On 10 December, a larger steam and gas plume was also visible above Whakaari.

“This was evident on our webcams at Whakatāne and Te Kaha as well as on satellite imagery.”

Mazot said when the weather allows, a larger plume can sometimes be seen from the Bay of Plenty coast above the island.

“The observations during the gas flight are the only signs of volcanic ash in the plume to date. Ash emission has not been visually noted from our webcams, or via Metservice’s analyses of satellite imagery.”

Mazot said without sensors on the island, they continue to rely on remote cameras and satellite imagery to monitor Whakaari.

“The changes in activity and what we observed from May to September suggest fresh magma is driving a change in activity. To date only very minor ash emissions have been noted near and on the island.

“We are planning an observation flight to make more observations and monitor potential changes in the crater area.”

A photo taken during the gas measurement flight on December 14, shows the volcanic ash emission from the active vent and the gas and steam plume drifting downwind.

Recent activity is consistent with moderate-heightened unrest.

Mazot said these levels acknowledge the current level of activity but also reflect the degree of uncertainty about the level of unrest due to the current lack of consistent, usable real-time monitoring data. The level of volcanic activity could escalate back to levels seen earlier in the year and the volcano can erupt with little or no warning.

GNS Science’s Volcano Monitoring Group and National Geohazards Monitoring Centre will continue to closely monitor Whakaari/White Island for any changes in activity.

“We will provide further updates when information becomes available,” Mazot said.

Further information about the Volcanic Alert Levels and what they mean can be found here.

For information about the impacts of the steam and gas plume should it reach the coast, follow the advice from:

• Bay of Plenty Emergency Management

• NEMA: What to do during volcanic activity

• Toi Te Ora Public Health: Volcanic Activity