How the experts decide if it's safe to visit White Island

Tuesday, 10 December 2019

First responders land on 'moon-like' ash after White Island eruption

When volcano experts from one of the Government's top research institutes visit Whakaari/White Island they go through a procedure to decide whether it's safe to make the trip.

But GNS Science didn't make that assessment this week because there were no plans to send any of its staff to the island during the week.

This 1.5 tonne tour helicopter was shunted off its helipad by the force of the eruption.

In a briefing to reporters on Tuesday evening, GNS senior vulcanologist Graham Leonard was asked if he would have gone to White Island on Monday. Six people who were on the island on Monday are confirmed dead and another eight are missing presumed dead after an early afternoon eruption.

Leonard didn't directly answer the question, but did say GNS had a framework for managing decision-making about whether staff went to the island and balancing up how much time they might be there.

* The science of the White Island eruption: A catastrophic burst of steam

* Whakaari/White Island eruption: Why were tours still operating?**

In previous weeks staff were able to 'visit the island for a time'.

As far as this week was concerned, he was not aware of any field work that had been planned.

'We've got our own procedures from a risk point of view for going onto the island and we certainly were aware that the activity had gone up,' Leonard said.

'We can manage that through a variety of approaches - either not going there, or controlling how close we're going. But because we were not actively doing anything on the island, or planning to do anything on the island this week, we were not making that decision for ourselves.'

In recent weeks there was a rise in indicators monitored at the island, including seismicity and volcanic chemistry. That increase in unrest, and the increased chance of an eruption that went with it, were communicated publicly through GeoNet volcanic alert bulletins.

'I guess the really important factor is this is a very active volcano. It has a large hot water and steam hydrothermal system near the vent, and that's got a lot of heat driving it from a magmatic system below,' Leonard said.

'So eruptions of the scale we saw yesterday can occur suddenly, as they did yesterday with virtually no immediate precursor signals because it's just a destabilisation of that very active steam and pressurised water system near the surface.'

Whakaari/White Island was New Zealand's most active volcano. It' was in almost continual eruption from 1976-2000, with another eruptive episode on-and-off since 2011. Several eruptions in recent years at the island happened at various alert levels, Leonard said.

'Because it is so active and there's so much energy there it's clearly capable of erupting with no immediate precursory signals. We've had those recent eruptions in the last few years but at those times … people have not been on the island.'