Hidden Danger Lurking under New Zealand

What’s boiling underneath the surface?

Researchers have found extremely hot temperatures and high fluid pressures one kilometre beneath New Zealand’s Alpine Fault. These findings have given scientists a closer look at what happens right before a major earthquake strikes and the potential discovery of a new geothermal energy resource.

The Alpine Fault is one of the largest plate boundaries in the world. It is also New Zealand’s most dangerous earthquake fault. Running for 650 kilometres along the South Island, the fault ruptures every 300 years creating an earthquake measuring a staggering magnitude of 8.

The last recorded earthquake of this scale was in 1717 when the earthquake lifted the mountains and rearranged the landscape horizontally. The next rupture is expected within the next few decades as the fault is at the end of its seismic cycle.

This is the first deep fault drilling before a major rupture and has given scientists an opportunity to take a more in-depth look at the build-up before a major rupture.

video: Drilling into New Zealand’s most hazardous fault.

Rupert Sutherland, Professor of tectonics and geophysics, Victoria University of Wellington and a team of international researchers drilled two large holes- the second hole reaching a depth of 893 metres deep. The deeper the scientists drilled, the higher the temperature, increasing at a rate of approximately 15 degrees every 100 metres. Rupert Sutherland, a researcher from the team, was shocked to see the rapid increase of temperature:

This is much higher than the normal rate of about 3°C per 100m in depth. At a depth of 630 metres, the water at the bottom of the drill hole was hot enough to boil, if it had been allowed to rise to the surface. The high pressures at depth stop it from boiling.

The team discovered a geothermal gradient as hot as the boreholes drilled into the volcanoes of the North Island. This is an exciting find as there are no volcanoes around the Alpine fault.

So how did this non-volcanic area become so hot?

According to researchers, the extreme underground heat can be attributed to two things; mountains being pushed higher and the breaking up of rocks.

During an earthquake,  fractured rocks are forced away in landslides and are carried to sea by rivers, therefore limiting the height of the mountain. During this process hot rocks from deep beneath the earth (about 30 kilometres deep, at 550°C) are pushed to the surface at a speed so quick they have no time to cool.

The second process, rock fracturing allows rain and snow to permeate into the mountain so fast it can move heat towards water wells in the valley. The flow has to be fast enough, so heat is not lost along the way. Hot water moving through rocks concentrates heat and then raises fluid pressure beneath the valleys.

The results of the drilling are not only important for New Zealand but for other countries with large faults that haven’t been investigated previously. It also means that researchers can now describe and even estimate what’s happening on a geological, rupturing fault.  This information will help scientists develop better computer models for monitoring earthquake rupture.

The conditions found underground could have obvious economic benefits for New Zealand by using the clean geothermal energy for local industry and communities. Their predictions are that similar hot geothermal conditions are present in valleys nearby.

More drilling and measurements are needed to establish the scale of this local resource, its possible uses, and if it is safe to develop.

Header: Mount Cook National Park, South Island, New Zealand, Shutterstock

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