New Zealand: Drilling Project Encounters a Very High Geothermal Gradient

Hellish conditions a scientific gold mine for drilling project (Nature.com)

Attempt to reach earthquake source fell short but yielded surprisingly hot rocks.

A failed effort to drill through a dangerous fault in New Zealand has served up unexpected scientific results that could help researchers to better understand how earthquakes happen. The project measured temperatures in excess of 100ºC at just 830 meters below the surface — an exceptionally high value at such a shallow depth.

GNS Science leads the Deep Fault Drilling Project that sought to drill through the Alpine Fault on New Zealand's South Island. After drilling ended and conditions in the hole reached equilibrium, the cable recorded temperatures of more than 110°C at a depth of 830 meters. The typical geothermal gradient increases at a rate of just 30°C per kilometer below ground, and a shallow borehole that the team drilled nearby in 2011 had a gradient of twice that. The gradient in the new hole reached as high as 150°C per kilometer, the researchers reported.

“It has this very high geothermal gradient, and it’s very intriguing on that account,” says Diane Moore, a geologist with the United States Geological Survey in Menlo Park, California. Despite the problems with the Alpine Fault project, she says, “it’s a very impressive body of work that they’re getting out of it”.

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