Fears for future of busy geyser

By ELEANOR BLACK

Rotorua's spectacular Pohutu geyser has been spurting for a record 233 days, but a retired engineer believes it could sputter out.

Lewis Vause, a hot water specialist, says that since the city's geothermal bores were closed in 1987, the geyser has spurted water and steam almost continuously when it should erupt only occasionally.

Pohutu will die if not allowed to set its own cycle and rest between eruptions, he says.

Twenty years of research have convinced him that the geysers at Whakarewarewa thermal park are interconnected, and influence each other.

He says the so-called recovery of the geothermal system - after the closure of 100 private bores used to extract heat energy from the geysers - was the result of natural regeneration which began six months before the closures.

Mr Vause now lives in Tauranga, but while working for the Forest Research Institute in Rotorua he found a link between Pohutu's eruptions and a pressure recorder at his office.

He could predict the next eruption by reading graphs which recorded the amount of water drawn through an institute bore.

A former colleague confirmed that the pair mapped a relationship between the institute bore and Pohutu's eruptions.

Mr Vause says: "The closing of the Rotorua bores in an attempt to further fill an already full geothermal system was a genuine mistake.

"The so-called decline of the geysers in winter was the penetration of deluge rainfall into the aquifer, cooling it off to temperatures too low to be effective."

Dr Tony Mahon, former geothermal coordinator for the Department of Scientific and Industrial Research, says that although the bore closures were successful in regenerating the geothermal system, other factors might be involved.

"What [Mr Vause] said was physically and chemically plausible. I can't tell you if he's right or wrong, but I have no doubt in my mind that Lew has made some very good contributions."

Rotorua consulting engineer Jack Just says Pohutu's continuous eruption may be due to a buildup of calcium carbonate in the rock tunnel through which the geyser flows.

He says the water stream becomes more powerful as it is forced through an ever-decreasing space and one day the hole will close.

But Dr Peter Wood, geothermal and minerals section manager for the Institute of Geological and Nuclear Sciences, says Pohutu is safe for the moment.

"There is no problem, providing the pressures are maintained in the system. There's a lot of water down there and it's not going to pump it dry."