Blazing temperatures under Southern Alps
Researchers have found some of the most extreme underground conditions anywhere on Earth beneath the Southern Alps, including temperatures similar to those in an active volcanic zone.
The surprise discovery may provide clues as to the conditions of a major fault prior to a significant rupture.
An international research team has discovered ‘‘extreme’’ geothermal conditions deep beneath the mountains, according to research published in the Nature journal yesterday.
Temperatures measured near the surface were similar to those found in active volcanic zones such as Taupo – yet there are no volcanoes in Westland.
The research team – led by GNS Science, Victoria University of Wellington and the University of Otago, comprising more than 100 people from 12 countries – drilled a borehole nearly 900 metres deep at a site near Whataroa in Westland. They were trying to establish the conditions of a major fault prior to a significant rupture.
The alpine fault is highly predictable, producing a magnitude-8 earthquake about every 300 years. The last such earthquake was 300 years ago.
At 630m deep, they measured water temperatures of 100 degrees C, hot enough to boil water. They had expected temperatures of less than 40C.
Drilling further, they determined that the borehole’s geothermal gradient – how quickly temperature rises as you go deep into the earth – was unlike any known active fault in the world.
‘‘Nobody on our team, or any of the scientists who reviewed our plans, predicted that it would be so hot down there,’’ said lead scientist Professor Rupert Sutherland, from Victoria University of Wellington.
He said they found some of the ‘‘most extreme underground conditions on the planet’’; the conditions were similar to that of boreholes drilled directly into volcanoes.
It was likely a mixture of two processes, he said. Rocks of about 550C are uplifted from 30 kilometres deep with such speed they do not cool down. Fractured rocks allowed water to seep into the mountains beneath valleys, further uplifting heat, before being flushed by rain and snow.
The next step would be to determine how extensive the geothermal resource was and whether using it was viable, Sutherland said.
Project co-leader Dr Virginia Toy, from the University of Otago, said the discovery was unexpected, and no major faults worldwide were known to have such a high geothermal gradient.
‘‘It turns out this is just as hot as the Taupo volcanic zone, which is virtually an active volcano. It’s astonishing.’’
Development West Coast chief operating officer Warren Gilbertson said it could be a great opportunity for a local industry. ‘‘The location of geothermal activity and its possible benefit and association to the dairy and tourism sectors provide real opportunities from an economic perspective,’’ he said.