This week's tragedy at White Island has prompted wider questions around how New Zealand's volcanic risks are managed – and whether private companies should be able to make their own calls.

In charge of monitoring all of the country's key volcanoes is GNS Science, whose NZ Volcanic Alert Level (VAL) System sets levels ranging from zero to five.

The government research agency also sends out bulletins to around 300 recipients – councils and companies among them – to advise of any changes in activity.

This information is based on an expert consensus and checked off by different people in the team to ensure it's been communicated correctly.

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But GNS' responsibilities didn't reach as far as preventing people or operators from going near volcanoes amid heightened unrest – and its role was instead an advisory one.

Two years ago, local and national authorities agreed to a Memorandum of Understanding for White Island that set out direction and responsibilities around readiness and response.

Although the island was privately owned by the Buttle family, Bay of Plenty Civil Defence group was in charge of emergency management.

Yet whether any authority could order tours be stopped over rising volcanic activity was unclear.

"As far as having a government agency that would actually prevent someone from going on to the island, no, there isn't one," GNS Science volcanologist Geoff Kilgour said.

White Island Tours relied on monitoring information from GNS, and also had its own risk and safety protocols that informed its decisions to take tourists ashore.

On Monday, and over the weeks before, the company had deemed alert level 2 – signalling "moderate to heightened unrest" – as safe to visit the island under.

That was despite weeks of heightened activity and warnings from GNS that the volcano may be "entering a period where eruptive activity is more likely than normal".

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While GNS experts could field calls from stakeholders worried about potential risks, things didn't work the other way around, with scientists stepping outside the monitoring remit to directly discourage operators from going near an unsettled volcano.

University of Auckland volcanologist Professor Shane Cronin described White Island's governance arrangement – and also that of Tuhua/Mayor Island and Mt Tarawera – as a "grey area".

"At White Island, where you get generally small eruptions, the management, or who has responsibility, is a bit unclear," Cronin said.

Tongariro's system

That wasn't the case with Tongariro National Park – home to three monitored volcanoes – and Mt Taranaki, all of which were directly managed by the Department of Conservation (DOC).

While using the VAL system as its underlying tool, at Tongariro, DoC also employed its own volcanologist and public safety senior ranger, and managed a volcanic alarm system.

"The extent at which we manage volcanic unrest varies at each of the volcanoes due to the distinct volcanic hazards and their proximity to assets and visitors to the park," DoC's Central North Island operations director Damian Coutts said.

"Current actions can range from ensuring the public and visitors are aware of the volcanic environment and socialising the changing level of unrest to the public through to closure of tracks and other assets, while the DoC volcanologist and GNS work through the likely level of risk."

On Ruapehu, set measures include recommending people not to enter the crater basin when the alert level is at 1, and closing access to the summit hazard zone altogether when the level rises to 2.

"The department warns visitors not to spend a lot of time on the summit plateau in any circumstances and raises the warnings depending on VAL level and our own analysis of the likelihood of eruptions based on lake temperatures."

The Department of Conservation closely manages volcanic risk in Tongariro National Park. Photo / File
The Department of Conservation closely manages volcanic risk in Tongariro National Park. Photo / File

At Tongariro and Ngauruhoe, if the risk begins escalating from zero, signs are put up and meetings are held with iwi, groups and GNS; if it rises to 2, the popular Tongariro Alpine Crossing is closed.

"While the department has made significant attempts to reduce the risks to visitors in the park from volcanic activity and natural hazards there will always be some residual risk that it is not possible to remove," Coutts said.

"The risk of unheralded eruptions will remain, but we can work to minimise that risk through the application of science and good safety systems."

'This is not a good thing'

Cronin believed DoC had done a good job of managing risk in the park, and agreed having such a decision-making authority overseeing other volcanoes like White Island was "probably a good way forward".

He thought this could take pressure off GNS so it didn't come in danger of making "quasi-risk management decisions".

"As a scientist, working through the Department of Conservation is clear and easy when you seek access to do your research," he said.

"Similarly, in a crisis you've got good recommendations about restriction of access for the general public: but for a place like White Island, who knows where you'd start."

If tourism operations resumed at the island, Cronin felt the tours should be restricted to boat – or at least out of the path of eruptive surges.

Tom Wilson, an Associate Professor of Disaster Risk and Resilience at the University of Canterbury, also believed questions needed to be answered.

"We need to go through a really robust thorough discussion around what's happened, why it has happened, and do we have volcano risk management structures and processes that are fit for purpose in a contemporary, multicultural society," he said.

"That's something I don't think we can deal with in the immediate aftermath – there are still bodies on the island – but it's something that we need to work through carefully, inclusively, and transparently. This is not a good thing."