Auckland Council should reject a proposal to build homes on one of the city's most prized volcanoes, says the Geoscience Society.
Crater Hill, on the edge of the Manukau Harbour, is seen almost at eye level out of aeroplane windows by millions of people a year, says soceity president Dr Adrian Pittari.
"It is the best preserved tuff volcano in Auckland with the best example in New Zealand of a lava lake that has partly drained back down the volcano's throat at the end of the eruption," he said.
The privately owned Crater Hill has been partly rezoned for up to 575 houses at the request of its owners, the Self family.
The independent hearings panel considering a new rulebook for the city, or Unitary Plan, has recommended the outer slopes of the tuff volcano and crater lake be turned into single and mixed residential housing.
Pittari said the society and other organisations have been advocating for permanent protection for the nationally important part of Auckland's volcanic heritage for more than 25 years.
"Crater Hill is not entirely pristine, but the 80 per cent that is untouched makes it one of Auckland's most aesthetically attractive and iconic volcanoes.
"Auckland undoutedly needs to address the housing issue but we argue this should not be done at the expense of our volcanic heritage.
"We call on Auckland councillors to follow their own Unitary Plan and reject this recommendation," he said.
The council's proposed Unitary Plan supported preservation of Crater Hill, but the independent hearings panel disagreed and recommended a mix of housing and open space.
Geologist Bruce Hayward said Crater Hill is the second-best preserved volcano in South Auckland after Mangere Mountain.
It is ranked the eighth most-valued volcano in a report to the Ministry of Culture and Heritage, which is assessing the case for nominating Auckland's volcanoes for World Heritage status.
"The panel has decided to accept almost in its entirety, without notification and therefore informed discussion and hearings, the owner's proposal to inflict still further damage on our city's volcanic heritage," said Hayward, who wrote the book, Volcanoes of Auckland.
He said the panel had ignored decades of documentation of the heritage values of Crater Hill and thumbed its nose at Auckland Council's own evidence that strongly advocated keeping the volcano intact.
Hayward said over the years there had been attempts to secure the crater and its protection by local and regional councils.
During this period the owner had exercised an historic quarrying licence to nibble away at one side of the crater and remove a small scoria cone.
In recent years, he said, quarrying had stopped and most of the excavation had been backfilled so only a little work was needed to restore the east side of the crater.
"The residential zone covers most of the outer slopes of the tuff volcano with the denser mixed-housing zone filling the part of the crater damaged by the owner's quarrying activities.
"The crater lake is already in council ownership and most of the rest of the inside of the crater is proposed to be open space," Hayward said.
Crater Hill is listed as an outstanding natural features in the Manukau District Scheme and Auckland Regional Policy statement.
"Well into the 21st century, one would have thought that what is now proposed for Auckland's last remaining privately-owned volcano would have been impossible," Hayward said.
Volcanic Cones Society spokeswoman Linda Vink said the society had supported the former Auckland Regional Council's efforts to buy Crater Hill.
It would make a great premier park for South Auckland, she said.
It was "totally ludicrous" for houses to be built on the cone, she said.
In 2007, the former Manukau City Council bought the privately owned Pukaki crater south of Mangere near Auckland Airport for $6.7 million as a public park.
The Herald has not been able to contact the Self family.
Emma Bayly, a planner acting for the Self Family Trust, told the panel in February that the trust sought to rezone the land from rural production to residential zones while maintaining about 80ha of open space.
The trust planned medium-density housing of up to 300 houses in the eastern part of the site next to the Southwestern motorway, and up to 275 low-density houses on the lower slopes southeast and west of the crater.
The open space would include a conservation area over the crater rim and land extending to the coast southwest of the crater to give a strong physical and visual connection to the coast. An esplanade reserve would be vested at the time of development, Bayly said.
"The zoning approach introduces residential zones that will encourage development at a scale that is compatible with the natural, cultural, archeological and landscape qualities of the subject land," she said.
Auckland councillors will consider the fate of Crater Hill when they consider recommendations on the Unitary Plan next week.
A spokeswoman for the Department of Culture and Heritage said Auckland's volcanic field is one of eight sites on New Zealand's World Heritage tentative list.
In 2014, the department commissioned an initial feasibility study to assess the case for the field meeting the threshold for World Heritage status.
At the time, the spokeswoman said no formal nomination had been made.
"If a formal nomination is undertaken, the specific volcanic sites to be included would need to be confirmed. There is no certainty that a nomination would include Crater Hill.
"The ministry is aware of the Independent Hearings Panel's recommendation on the Auckland Unitary Plan to partially extend the Rural Urban Boundary and will not be commenting further while the recommendations are being considered by Auckland Council," the spokeswoman said.