A geologist is calling for a halt to development in Rotorua areas where he says poisonous geothermal gases are silently killing people.
Will Esler, a Waikato University earth sciences student, says poisonous gases, especially hydrogen sulphide, will continue to silently kill Rotorua people.
There have been 11 deaths in Rotorua in the past 50 years attributed to hydrogen sulphide but Mr Esler says the true death toll isn't known.
The entire Rotorua township was built in the wrong area, he told the Daily Post.
While settlers in the 1880s probably thought they were right to establish the Rotorua township in warm geothermal hubs, the hydrogen sulphide seeping off geothermal features were "silent killers", Mr Esler said.
"Rotorua has been put in a rather silly place. Europeans went out and set up this town without regard to hotspots and we are now living with the consequences."
Mr Esler said the areas he considered dangerous included anywhere hydrogen sulphide was concentrated, such as the land at Valentine's restaurant, parts of Tarewa Rd, parts of Sophia St, parts of Whittaker Rd, Ohinemutu and Whakarewarewa.
While little could be done now to move the Maori villages in areas like Ohinemutu and Whakarewarewa, the Rotorua District Council should re-zone areas to ensure future development could not take place in dangerous areas, he said.
He envisaged that under such a policy, when houses became worn out, they would be removed and the land would be zoned so there could be no more building on it.
He said Rotorua residents had been put at risk because of casual town planning in the past. He did not blame the council, he said, because it had inherited the problem. But he doubted whether any council would get enough support from the community to make such a change.
"We have to wait for a disaster and for hundreds of people to die before there is any action."
Council planning services manager Tracey May said the council was going through a district plan review, which included the zoning of land.
"Natural hazards, and the constraints that these place on properties are a fundamental part of this research, the outcomes of which are taken into account when looking at zoning," Ms May said.
Ohinemutu resident Dawn Kereopa said there was no way local Maori would stop living on their land. "That's ridiculous. We have lived here for years and there have never been any problems."
Mr Esler is about to conclude research into Rotorua's geology, which has led him to quip that Rotorua offers a greater variety of ways to die at the hands of nature than any other New Zealand city.
Rotorua's geothermal past meant that in the future, residents would be likely to die from scalding, incineration, sandblasting, live burial, poison gas, drowning, lahars and landslides.
"Possible methane fireballs from gas trapped in foul lakebed ooze are a new attraction."
However, he pointed out that residents in Auckland and Wellington were at greater risk of mass death because they were closer to earthquake faultlines.
Mr Esler also believes Lake Rotorua will drain to a swamp in the next few thousand years.
He said the lake had subsided at an average rate of about 1.6mm a year for many thousands of years.
"On present trends, the lake would be reduced to a swamp in a few thousand years and drained completely in only about 5000 years."
He said the lake was dropping by 6 litres a second. On the up side, he said the increased 0.6ha a year of lakebed meant the soon-to-be new owners of the lake, Te Arawa, were in for what could be real estate worth more than $1 million a year.
However, Te Arawa might have to wait a few thousand years to cash in on the accumulated asset.
Mr Esler, expects to finish his thesis early next year.
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