Taparoto Nicholson sensed there was something peculiar in the air - and it was more than just Rotorua's signature pong.
The morning of September 3 was a bright blue one at the Whakarewarewa Valley, as Mr Nicholson took his usual early walk around the winding, scrub-covered trails at Te Puia.
The tourist attraction's long-serving cultural adviser strolled past a steaming but still dormant Papakura geyser.
In 2013, it had briefly caused a stir among scientists with a small show of activity.
A few hours after Mr Nicholson's stroll, a fellow staffer walked into his office to report Papakura was back. For 36 continuous hours, it gushed and spluttered, throwing steam and water up to 4m into the air.
"There was something about that day, there really was," he said with a smile.
It came in stark contrast to the morning in 1979 when Rotorua's then district geologist watched it fall silent from his Tihiotonga home above the valley.
"I looked down in it every morning, and suddenly there wasn't a steam column," Ted Lloyd recalled.
Worryingly, he'd seen the very same thing happen at the Wairakei geyser valley.
Papakura had been a star of Rotorua's bubbling landscape - it took centre-stage in old publicity pictures, dwarfing Maori locals posing nearby in traditional war dress, and on cold winter days could be seen spouting high above the fog clouds.
Its demise had been preceded a decade earlier by the valley's crown jewels Wairoa and Waikite, which both once wowed tourists by firing jets tens of metres into the air.
As the cherished geothermal features began to decline, one explosive chapter gave way to another when Mr Lloyd and fellow scientists, led by Auckland University physicist Associate Professor Ron Keam, squared the blame on geothermal development.
In 1978, Associate Professor Keam launched a lengthy legal battle to stop the Ministry of Works and Development from taking water from the Waimangu geothermal field south of Rotorua, arguing its relatively recent birth in the 1886 Tarawera eruption had meant its complete history could be studied.
A landmark court decision in his favour suddenly made it necessary to apply for water rights under the Water and Soil Conservation Act, meaning use of geothermal water and steam had to be weighed up against impacts on the environment.
This eventually helped push the focus on to Rotorua itself.
The Rotorua Geothermal Field, which underlies much of the city and the southern fringe of Lake Rotorua, is believed to have been active for tens of thousands of years.
For this incredible landscape, we can thank young and active rhyolitic volcanism associated with the wider Taupo Volcanic Zone, whose stretched and fractured crust has been permeated with magma that, in some places, has brought temperatures of at least 350C at depths of less than 5km.
The Rotorua field's centrepiece, Whakarewarewa, boasts the largest remaining concentration of geysers in New Zealand.
Still intact are Pohutu, which continues to regularly erupt water up to 30m into the air, and neighbouring geysers Prince of Wales Feathers, Kereru and the large hot pool Te Horu.
With a source of heating readily available underground, more than 900 shallow wells - most of them less than 200m deep and piping up fluid at temperatures of up to 200C - were drilled beneath the city to serve hot water to homes, hospitals, schools and businesses. Yet this was done without a clear understanding of what would happen to the field itself, and between 1967 and 1985, the natural heat flow dropped a dramatic 30 per cent. With this came the loss of many spectacular natural geothermal features.
Ultimately, the Government was forced to respond by rescinding the Rotorua Geothermal Empowering Act and ordering that all bore owners within a 1.5km radius of the Whakarewarewa Valley be closed.
In 1986, they began receiving cleanly typed notices from the Ministry of Energy warning them that it was a crime to "impede or obstruct" the inspectors as they went about shutting the bores down.
"The bore owners had spent a lot of money on having their bores put down, so it became very controversial," Associate Professor Keam said last week.
"This caused a lot of problems, with a number of people sometimes taking even direct action to try to discourage them being shut down."
A former ministry contractor vividly recalled protesters banging on the walls of the Rotorua branch so hard it felt like the building was shaking, before one person threw a brick at the window.
Ted Lloyd summed up the tumultuous time: "I wouldn't want to go through it again."
Within only 2 years of the closures, however, the scientists' predictions began proving correct.
"Those guys had pretty good science and experience - they'd seen the destruction of the geothermal features at Wairakei, The Spa and Ohaaki - and they knew that if they got in quick enough and stopped it, we'd be able to recover them," Brad Scott said.
The Herald met the GNS Science scientist at Spring 653 at the back of steaming Kuirau Park, where geothermal activity has returned to levels not seen since the 1920s.
This spring, sitting in a vacant, overgrown section in the middle of Rotorua's central suburbs, was an empty basin in the 1980s and had been crudely used as a rubbish tip.
This dramatically changed when the number of bores dropped from 1100 to 140, slashing the draw of geothermal water from 30,000 to less than 3000 tonnes each day.
Spring 653 now looked the way it was described in crusty old records: overflowing and at a near-boiling temperature.
Mr Scott estimated that nearly 60 per cent of Rotorua's geothermal features had now recovered, while another 15 per cent, including Papakura, were showing promising signs of life. While Wairoa hasn't received any geyser-fuelling geothermal fluids since the early 1960s, water levels inside it had risen perhaps 2m in the past two years.
"Rotorua is a massive geological experiment - can we actually manipulate a geothermal system? - and it's really exciting to see an experiment that's been running on the blunt end of 40 years now actually showing good fruition."
In the so-called "Whaka" area - spanning through the Whakarewarewa village and Te Puia - the recovery was being observed in different ways. On its eastern side, near the village, geothermal features had been shown to rise and then fail, while others had risen and hung on in a recovered state.
The best cases have happened around Lake Roto-a-Tamaheke, while the lost features around Te Puia have been slower to return.
Some, like the Puapua hot spring and natural cooking pool Ngararatuatara had survived in a steady state since the bore closures, while the water level of the cauldron-like chasm Te Horo had risen several metres.
While regular checks of the features are made by scientists like Mr Scott, who compare water and chemistry data with the story underground monitor bores are telling them about the geothermal aquifers, the responsibility of managing them falls to the Bay of Plenty Regional Council.
It monitors around 40 "surface features" within the field, which is overseen through a mix of plans and policies, including the Rotorua Geothermal Regional Plan that rekindled more debate when it was first put in place in 1999.
Regional councillor Paula Thompson said the recovery had highlighted the importance of managing the resource sustainably.
Over recent years, innovations such as heat-exchanger technology had brought new ways to harness the energy source without harming it, while clever new uses for it were being explored through the just-launched Toi Moana Bay of Plenty Regional Growth Study.
Rotorua Mayor Steve Chadwick saw opportunities for more jobs and cash for the region.
"To see this life bursting forth, literally, has got us all very excited, but I actually see potential in us capturing some of that energy and harnessing it for initiatives that could grow our economy."
Clearly, the restoration of further hot springs and geysers would also be a huge boon to a local tourism industry that contributed around 10.5 per cent of Rotorua's GDP, served as the city's biggest employer, and last year recorded 2.4 million visits and $468 million in visitor expenditure.
For Whakarewarewa, the revival of Papakura and features like it had been a hugely exciting development for the valley's visitors and residents, Te Puia chief executive Tim Cossar said.
"Visitors have been drawn to the geothermal features of the valley, and the hospitality of our people, for almost 200 years and it is an attraction that is as important today as it was then.
"These recent developments add a new layer to this offering - and it's right here in our back yard."
Just as important as the economic potential, Ms Thompson said, was the need to invest in ongoing research about sustainable use, the extent of the known resource, and finding new deep sources.
Mr Scott said he ultimately hoped the tough decisions made in the 1980s would ensure the survival of what was a global hotspot for geothermal research - it offered the basis for the evolution of many geothermal models and volcanic and geological theories.
"Globally there are not many large- scale geothermal systems, maybe 30 to 40, so New Zealand is very unique as we have seven or eight of the world's better examples."
And Rotorua had not only proven that geothermal exploitation could silence springs and geysers, but also that this could apparently be reversed.
While the recovery of geysers like Papakura were a small part of a big picture, their global scarcity made it special just to have one or two revived.
"I'm just happy some of the team who made the hard calls 30 years ago are still around to see it has paid off," he said.
"They got to see many of the 200 to 300 features we used to have destroyed with exploitation - they are the heroes who realised what we were losing and stood up for them."
Mr Nicholson said that, for local iwi, the importance of having the geysers back would be immeasurable.
"The cultural significance of all these features is such that they were all given names by local people here as far back as 1750."
Some bear the name of Te Arawa chief Hatupatu, who in Maori folklore escaped the fearsome bird-woman Kurangaituku by leading her to her death in Whakarewarewa's boiling springs.
"These waters, hot or cold, were gifts from God, and the geysers, especially, were a sign that life here needed to be respected."
If it was the case that these gifts were being slowly returned, hapu would be pleased their land was healing, he said.
"Is there a scientific reason for this? I don't know, but as local Maori, we'd see that as a tohu pai - a positive sign."
Icons of Geyserland
The geyser fell silent in 1979, after 90 years of continuous eruption, highlighting the damage to geysers caused by private and commercial boring in the area. In what may be a world-first, the resulting bore closure programme of the 1980s has seen Papakura Geyser rejuvenated and showing signs of life again after nearly 35 years. On September 3, scientists were excited as it gushed water and steam 4m into the air continuously for 36 hours.
One of the main attractions of Te Puia, Pohutu survived the impacts of pressure from geothermal bores, and today can be seen to erupt at a height of 30m, up to 20 times a day. Its natural water cannon is activated when geothermal fluids inside its plumbing start to boil and create steam. Pressure builds inside Pohutu's underground chamber until it eventually forces its way upwards through the geyser vent and shoots water and steam up into the air. Recently ranked in the world's top five geysers by Lonely Planet, the geyser is regarded as the most "reliable" geyser on earth.
Meaning "water seen from afar", this historic geyser was once the most commanding sight in the Whakarewarewa Valley. Such was its fame that Rotorua's Fenton St was designed to provide visitors with a better view of it from the old post office. It stopped erupting in 1967.
This large hot pool, also known as The Cauldron, used to erupt regularly to a height of 2m to 7m, until all activity stopped in 1972. By the 1980s the water level had fallen several metres, but after the bore closures the water started to rise and in January 2000 it started to overflow. It is closely linked to Pohutu, as air-cooled water from the famous geyser sometimes lands in Te Horu's vent and is believed to delay the next eruption. It seems we will have to wait a little longer to see a return to former glory.
PRINCE OF WALES FEATHERS
Located just 2.5m from Pohutu, this geyser started erupting in June 1886 at the time of the Tarawera eruption. It is often referred to as the "indicator" as it will perform two to three times before Pohutu is seen to erupt.
There were regular, large eruptions from this geyser in the late 1890s until the 1920s, but there have been fewer since. No eruptions were observed between 1972 and 1988, but since 2000, small eruptions have became more common again.