Southern Alpine Fault's heat a potential game changer

Scientists studying the South Island's Alpine Fault have discovered some of the hottest ever temperatures in an active fault zone.

The geothermal energy is being described as a potential game changer for the West Coast.

Boreholes were drilled 900m into the fault, in an attempt to find out more about the conditions in the earth's crust during an earthquake, only to find it was five times hotter than they expected.

But there are no volcanoes anywhere at the drilling site near Whataroa in Westland.

Lead scientist Rupert Sutherland explains why it is so hot.

"Movement on the fault during earthquakes has uplifted rocks from 30km deep where temperatures are 550 degrees centigrade."

He says they cool on their way up but not fast enough. That heat is concentrated in the water beneath the valleys, but doesn't make the fault more likely to rupture.

Mr Sutherland describes the alpine fault as the most hazardous in the country. It's where the Australian and Pacific plates meet and runs virtually the length of the south island.

The fault ruptures every 300 years, producing a magnitude 8 earthquake. The last time it's thought to have ruptured was in 1717, exactly 300 years ago.

Mr Sutherland says the economic benefit from the geothermal resource could be huge.

"You can use it for the tourist industry; you can use it for a whole range of industrial processes like wood drying or agriculture, growing tomatoes or pineapples."

Westland mayor Bruce Smith says it could be a game changer.

"If it's economically viable it'll be tapped by one of the power companies, it could be something as bizarre as growing prawns."

But there will need to be more drilling before that economic potential can be realised.