Explained: What’s going on at Whakaari/White Island?

• Whakaari/White Island has shown “minor eruptive activity” since August 9, raising its alert level to three.
• Ash plumes from the volcano disrupted a dozen flights to local airports, now resumed.
• Officials say airborne ash is unlikely to fall on the ground in the Bay of Plenty.

Bouts of unrest and eruptions certainly aren’t out of the ordinary for New Zealand’s most active volcano – and that’s just what’s been occurring at Whakaari/White Island over the past six weeks.

Since August 9, scientists have been observing “minor eruptive activity” at the Bay of Plenty offshore volcano, prompting its alert level to be raised to three.

Because of the ash it’s been throwing up, making for a grey plume visible from the mainland, some 20km away, officials were forced to cancel or delay a dozen flights to local airports this morning.

The grey plume thrown up by the volcano can be seen 20km away. Photo / B Scott, GNS

Flights have since resumed, with agencies closely monitoring conditions.

While most of the ash within the plume has been carried away by dominant westerly winds over the sea during the past few weeks, a northerly change overnight sent it in the direction of the mainland.

However, that was only airborne ash high in the atmosphere and Bay of Plenty Emergency Management’s Lisa Glass said it was highly unlikely ash would fall on the ground in the Bay of Plenty.

Why is volcanic ash a risk for aircraft?

Waikato University earths sciences lecturer Dr Adrian Pittari said the ash consisted of “dusty” glass and rock particles, which rose into the atmosphere and was then carried downwind by air currents.

“Ash in volcanic plumes is considered a hazard to aeroplanes flying in affected airspace because it is sucked into their engines potentially clogging fuel lines, sticking on to engine surfaces and eroding parts,” he said.

“It can also interfere with electrical and computer systems, infiltrate cabin space and reduce visibility.”

In two well-known cases – British Airways Flight 009 over Indonesia in 1982 and KLM Flight 867 over Alaska in 1989 – flying through ash plumes knocked out engine power.

Will there be a bigger eruption at Whakaari?

Right now, there’s nothing to suggest that a bigger blow is imminent.

“Whakaari is known for producing small eruptions and it is unlikely that a significant eruption will occur,” Victoria University volcanologist Dr Simon Barker said.

Last week, GNS Science reported a new vent had opened at Whakaari.

Within the volcano, which rises some 1.6km from the ocean floor, magma at depth was driving “moderate to high temperature” gas and steam up through the open vent.

Whakaari/White Island size comparison.

The agency said that, based on episodes over the past 48 years, the activity could carry on for weeks to months.

“The level of this activity is likely to remain ‘annoying’ for a while if this magnitude of eruption continues,” University of Auckland volcanologist Professor Shane Cronin said.

“By annoying, I mean that the semi-regular puffs of steam and gas cause unease as well as justified precautionary reactions by the aviation community.”

Cronin added that the ash content of the plume was generally low and of little hazard to people.

“The open vent situation is in many ways comforting, because this allows a relatively free and steady release of gas and magma pressure,” he said.

“This means that sudden large explosions are less likely – these are caused by trapped gas and a blocked-vent situation such as was the case in 2019.”

Still, he said it wasn’t helpful that there weren’t any seismic stations currently working on the island, leaving scientists to rely on measurements collected by flights and satellites.

“Without on-ground measurements, we can only guess at how much magma is rising to the surface and driving this current phase of eruption.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.