A long abandoned geothermal bore has burst into life at a Rotorua marae this week, throwing a column of water, steam and mud some 30 metres into the sky and coating nearby buildings and cars in a fine white residue.
The eruption began about 4.30pm at Tarewa Pounamu Marae on Tarewa Road and was still going strong the following morning, drawing a steady stream of onlookers to the edge of the cordon. At least five buildings on the marae grounds were affected, among them a kaumātua flat, which is a unit set aside for respected elders, and an office.
What started as steam and a scatter of small rocks soon turned to hot water. One resident described a murky white plume that dried to a powder on car bonnets and window sills, most likely sulphur laden water thrown up from deep underground. The mess washed off with warm soapy water and no structural damage to the buildings was reported, but the sheer scale of the spout left no doubt about the forces at work below the surface. By the second day the plume had fanned out wider while climbing a little less high.
Rotorua Lakes Council said the source was a grouted private bore that had failed, allowing water, steam, mud and concrete to spray into the air in a geyser like eruption, as reported by the Rotorua Daily Post. The bore had first been sealed with grout back in the 1980s, and the exact reason it gave way after four decades is still being pieced together.
The marae general manager, who lives on site, had noticed a lot of activity in the geothermal pools behind her house in the lead up to the blowout. Those pools have since dropped, because the pressure that once fed them found a new and far more dramatic escape route through the failed bore. It is the kind of plumbing only Rotorua deals with, a city built on a shallow and restless geothermal field where heat, gas and mineral water are never far beneath the footpaths.
Hemi Waerea, of the Ngāti Kea Ngāti Tuara hapū, watched the eruption widen over the course of the day. “The hole is sort of getting bigger,” he said.
The job of shutting it down has fallen to specialist well drillers. Dirk Hermson, of Barham United Welldrillers, was blunt about the task ahead. “We’re here to kill it,” he said. “It can be quite challenging.” The plan is to feed a steel pipe down the bore, then pump in cold water and cement to choke off the flow and reseal the hole. Hermson believes ground movement caused the old casing to fail. Regrouting was expected to take a couple of days once it began.
An increase in geothermal activity around Rotorua is not unusual after a wet spell. A council geothermal inspector noted there had been a slight lift in activity across the city following recent heavy rain, which is a normal response and one that usually settles as the ground dries out. The top of the South Island and parts of the North Island had been soaked over King’s Birthday weekend, with Golden Bay alone recording more than 270 millimetres in a single day.
Rotorua sits on one of the most accessible geothermal systems in the country, part of the wider Taupō Volcanic Zone that stretches from White Island through to the central plateau. For generations the heat has been a gift, warming homes and pools and giving Whakarewarewa its famous geysers. Hundreds of private and commercial bores tap the same reservoir for heating and bathing, and the Bay of Plenty Regional Council manages the field carefully to keep the surface features alive, as set out in its overview of the Rotorua geothermal system. When extraction was wound back in the 1980s, dormant geysers and springs slowly came back to life, a reminder that the pressure underground is always looking for a way out.
The flip side is that old and forgotten infrastructure can fail in spectacular fashion. Rotorua has seen geothermal blowouts before, from steam and mud erupting through city streets to a motel bore that suddenly began blasting steam and bubbling water. Each case carries the same uncomfortable truth, that a bore drilled and capped decades ago is only ever as secure as the grout holding it shut, and that grout does not last forever in hot, acidic, mineral rich ground.
For now the marae is making do with a noisy and steaming neighbour while the contractors work. The eruption has been more of a nuisance than a danger, a soaking, a clean up and a few coated cars rather than anything worse. It has also been a genuine spectacle, the sort of raw natural display that reminds Rotorua exactly what it is built on, and that the line between a tourist drawcard and a headache can be as thin as a single failed pipe.
Once the bore is sealed and the pools behind the marae settle back to their usual gentle simmer, the residue will wash away and the story will become another entry in the long history of a city that lives, quite literally, on top of the heat.
Have you seen a geothermal blowout in Rotorua, or do you live with a bore of your own? Share your story in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
Leave a Reply