A court has heard that the owners of Whakaari White Island relied on GNS to manage and monitor the island and update them on any changes.
The judge-alone trial resumed on Wednesday, in which WorkSafe alleges Whakaari Management Limited, and its directors, Peter, Andrew and James Buttle made health and safety failings in the lead up to the 2019 eruption that killed 22 people.
WorkSafe's interview with the brothers in 2020 played in the Auckland District Court today.
The court heard the Buttles assumed tour operators and GNS Science were communicating about the ever-changing environment on the volcano.
James Buttle said the brothers could only say that the operators and GNS seemed to be sharing information.
"Well we understood the system and parameters under which they worked and we could only say as observers that they seemed to be doing it successfully.
"But... we had no role in managing of that [sic], because how can you, because actually we weren't involved in the discussion tree of making that decision... Whether it's safe or not to go to the island."
Peter Buttle said it would be impractical for them to try and keep up on a day-to-day basis.
Instead, it made sure GNS, Emergency Management Bay of Plenty and the tour operators could communicate.
"Well we did… we didn't do anything to try and keep up with the hazards and risks of the the island on a day-to-day basis.
"There is nothing we could contribute to that, not being volcanic experts. We can't look at the data that's being generated and make an assessment so anything we could do would be confusing rather than productive," he said in the recording.
The communication between GNS and operators was a two-way street, Peter Buttle said.
"And as we've said, GNS used the operators themselves to, to inform their decision-making about what was happening at the island.
"And there are emails around, you know, around where they have questioned the operator saying; can you confirm that this has occurred on the island or is anyone noticed any changes as a result of this certain activity that they have recorded in their research.
"So it was very much a two-way street if you like between GNS and the operators and how they managed the island on a day-to-day basis."
He said their involvement would increase the risk instead of mitigate it.
"It's a wild place out there at times and so they, they have to be making decisions on a day-to-day basis about whether they were going out to the island, not only volcanically but weather and all the other factors that come in to play.
"So essentially we, we couldn't get involved in that, it would be just … that would increase their risk rather than reduce their risk, I believe, if we'd got involved in it."
In the recording, Andrew Buttle responded to questions about the brothers' involvement in managing the volcano.
"When the tragedy happened we were down here, you know, and we were there and available.
"So [what] we're saying here [is that] we don't make ourselves hard to get hold of, or say we don't want to have anything to do with it."
Andrew Buttle said the brothers felt like they would have been contacted if they were needed.
"We are very much ... involved and sometimes we were sort of … I don't know, not pushed to the side, but it's sort of like 'Well yeah you're there, and we'll get you if we need you'."
In the recording, the brothers seemed emotional remembering the fateful day in December 2019.
"It's very hard for us because when the tragedy happened that was... it affected us deeply."
"The enormity of it was just unimaginable," Peter Buttle said.
Meanwhile, the Buttles have failed to have the charges laid against them dismissed or stayed.
Earlier this month, the Buttles sought a judicial review of Judge Evangelos Thomas' decision to continue the trial, but Judge Jane Anderson at the High Court in Auckland has dismissed the application.
Two booking agents are also on trial and it will resume tomorrow.