A lengthy review is under way to clarify who does what when Whakaari/White Island erupts, just four years after a memorandum was signed to confirm responsibilities.

Twenty-two people died after the crater exploded in December 2019, while tour groups were visiting.

The island's owners, the Buttle family, hold the rights to restrict, or prevent access to the volcanic cone, but Whakaari's distance offshore means it does not come under any city or district council.

Instead, Local Government Minister Nanaia Mahuta is automatically the territorial authority for Whakaari and 10 other offshore islands.

RNZ revealed last week that Department of Internal Affairs staff have spent months reviewing the minister's health and safety, civil defence and emergency management duties for the island.

Only to tell her: "It is not clear in the legislation how your role as Territorial Authority is intended to work in practice."

The department is now also reviewing a Whakaari Memorandum of Understanding signed with the Bay of Plenty Civil Defence Emergency Management Group in 2017, and expects this will take a year to finish.

In a statement, the department's general manager of policy and operations Martyn Pinckard says the memorandum worked well for the minister after the 2019 eruption but it will now be fine-tuned.

"In particular, a review could better define the high-level expectations that the Civil Defence Emergency Management Group and the minister can reasonably expect of one another; definitions of response and readiness activities and what each party is responsible for."

Nanaia Mahuta says she has territorial responsibility for Whakaari but health and safety elements are handled by other agencies. Photo: RNZ / Dom Thomas.

University of Canterbury disaster risk professor Tom Wilson says clarity is vital in natural hazard risk management.

"It's really important that everybody knows what their roles and responsibilities are for the management of that risk. So ensuring that that's very clear, and that we know who's meant to be doing what, becomes paramount."

National Party leader Judith Collins says Minister Mahuta's response to the Whakaari eruption has been "flawed".

"There seems to be little understanding as to who is actually in charge."

But Mahuta disputes this.

"I have territorial responsibility for Whakaari but in terms of the activities and what happened there, the health and safety elements are handled by other agencies."

WorkSafe has charged 13 parties with breaching health and safety rules leading up to the tragedy, including tourism operators, the island's owners, and two government organisations - GNS Science and the National Emergency Management Agency (NEMA).

NEMA pleaded not guilty in the Whakatāne District Court last week, but the other accused are yet to enter pleas.

The WorkSafe and coronial investigations are not enough for Judith Collins who still wants a Royal Commission of Inquiry.

"It seems remarkable to me that the government has so far refused to have a Royal Commission set up. We've certainly had them before with Pike River, [and] with the March 15th killings in Christchurch."

The government has said a public inquiry could risk overlapping, duplicating and prejudicing current investigations and reviews.

The Bay of Plenty Civil Defence Emergency Management Group declined to comment on the Whakaari Memorandum of Understanding.

-RNZ/Sam Olley.