White Island could see more ash-belching eruptions over weeks, months or years to come, a volcanologist says.
Today, GNS Science experts gave a 50 to 60 per cent chance of another eruption within the next 24 hours.
That was put down to a body of magma sitting at a relatively shallow depth beneath the volcano's crater, which had been sending up increasing levels of volcanic gas since Tuesday.
Scientists were still seeing comparatively high amounts of tremor within the system, along with vigorous bursts of steam and mud around the vent where Monday's eruption came from.
University of Auckland volcanologist Professor Shane Cronin outlined several potential scenarios over coming weeks.
"Right now, you've got a batch of new magma that's come up, over-pressured the system, and blown the seal at the surface," he said.
"If that magma continues to rise up, it has a reasonably good chance of getting to the surface; and if that happens, we would have a series of ash-producing eruptions that could continue for weeks, months, or years."
Another scenario was that the magma body began to subside, but remained where it was long enough to produce one or two small explosions – perhaps smaller than Monday's.
"But if fresh magma keeps getting supplied to the chamber system, then we could be looking at more explosive eruptions."
In any case, Cronin didn't expect any further blows to be larger than this week's.
That was because the amount of pressure that had been able to build up below a mineral seal beneath the crater lake, which had been in place since after the volcano's last big eruption in 2016.
"Because it wouldn't be anywhere as well sealed as it was, you can't provide as much as pressure, and so you can't produce an eruption as big," he said.
"So I don't believe we'd get a surge like we had the other day, but certainly ash columns that might reach 3km high.
"That's the sort of thing you could expect, and it's what's been happening throughout this volcano's history."
Another volcanologist, Dr Marco Brenna of Otago University, pointed to the eruptions at Mt Tongariro's Te Maari Crater in 2012.
In the first explosion, on August 6 that year, a gas and steam eruption came as a result of pressure built up within the volcano.
When a second, smaller eruption occurred three months later, it proved to be the sudden release of what had been left in the system.
"So, there was really no new energy or fluid coming in; it was just the original system releasing what had accumulated and re-pressurised over the months after the first event," Brenna said.
Whether that scenario might play out at White Island would ultimately depend on how much new magma was being fed into it.
Cronin said White Island – which has been in a period of unrest since 2011, and remained New Zealand's most active volcano - always had plenty of activity going on deep beneath it.
What lies beneath
"What drives the magma to the surface are volatiles, such as water dissolving in the magma, which pushes it up and also makes it expand, or just the pressure of the magma in the system itself," he said.
"It's a little bit like a water aquifer, in that you have magma that is very deep below the volcano, but the load of all the rock around it squeezes it.
"And that's coupled with the constant supply of magma into the bottom of the storage system.
"At White Island, we expect that the magma is stored within the crust between 12km and 16km deep.
"So if you keep producing new magma and putting it into the central crust, that raises the pressure, and the magma is squeezed up toward the conduit of the volcano."
Once it entered the volcano's upper system, an eruption was more likely to happen.
"As I said, if the magma continues to rise, then we'll see some small eruptions," Cronin said.
"Either way, it will be a long time before people can ever return to the island."
Brenna said high concentrations of gases would be lingering over the island right now: among them, carbon dioxide, sulphur dioxide, hydrogen sulphide and chlorine.
Some monitoring equipment had been affected by ash, and one remote camera was expected to stop functioning today or over the weekend.
"Our remote stations are solar powered, and some data transmission will stop when the North Rim camera goes down due to ash covering the solar panels," GNS Science volcanologist Graham Leonard said.
"Almost all the monitoring equipment is still functioning."
The National Geohazards Monitoring Centre was operating 24 hours a day, and any changes would be immediately passed on to emergency services.
GNS also said there was an "extremely low" likelihood of any potential ash affecting the mainland, but people may smell gas, depending on the prevailing wind direction.