Published online 17 December 2008 | Nature | doi:10.1038/news.2008.1317

News

Drillers hit Hawaiian magma

Chance discovery allows up-close study of inner-earth processes.

A geothermal drill rig in Hawaii has for the first time tapped into intensely hot, granite-like magma — allowing scientists to observe in place the process through which continents are born.

Researchers and an energy-services company inadvertently cut into the magma body at about 2.5 kilometres below the surface on the Big Island of Hawaii. They hope to turn the site – currently an operating geothermal development – into an observatory for scientific studies.

"I've worked in this field for more than 35 years, and I've never seen anything like this," says Bruce Marsh, a geologist at Johns Hopkins University in Baltimore, Maryland, who was called in for analysis.

Pay dirt

Ormat Technologies, a firm based in Reno, Nevada, that led the drilling, hit the magma in 2005 at the Puna Geothermal Venture well field, which provides about 20 per cent of the electricity locally on the island. Team members presented their results on 16 December at the American Geophysical Union meeting in San Francisco, California.

The company generates energy from steam heated by Earth's interior to temperatures of about 350 °C. The magma, when the drillers hit it, was about 1,050 °C — so hot it dislodged carbide teeth from the drill bit and caused the drill string to seize up, says William Teplow, a consulting geologist with Ormat.

Most of Hawaii, a volcanic island chain, is composed of the dark iron-rich lava known as basalt. In contrast, the granitic magma was a clear, molten glass, composed of about two-thirds silica. Continents are made of such lighter material.

Island discovery

At a news briefing, team members said the granitic magma was sandwiched between basalt layers — suggesting that it had differentiated, or chemically separated, out from the darker material over time. This may be the first time "the actual process of differentiation of continental-type rock from primitive ocean basalt has been observed in situ", the team said.

Much to the scientists' surprise, the magma was what Marsh called "a docile animal", with few bubbles from volatile gases. In a typical geothermal well, engineers must constantly monitor well conditions because pressures can run to 2,000 pounds per square inch, increasing the risk of blowouts. The Puna field is also surrounded by an extremely active seismic zone, which experiences 10 to 12 small earthquakes a day.

ADVERTISEMENT

Preliminary geochemical analysis indicates that the magma may have erupted onto the surface in 1924, then undergone more chemical processing underground before erupting again in 1955. The team plans further analyses, of lead and radon isotopes in the magma, to pin down this timing. 

Commenting is now closed.