Drillers in Hawaii Encounter Magma

A geothermal power company drilling a mile and a half deep on one of the Hawaiian Islands has for the first time encountered an undisturbed chamber of magma, or molten rock, scientists reported this week.

Before the discovery, which was made in 2005, the only access to magma had been on Earth's surface -- in the form of lava from volcanoes.

The 2,000-degree Fahrenheit material in the chamber is undergoing a complicated transformation that may give geologists the first real-time look at how the silicate-rich rock of continents is formed.

"This is Jurassic Park. This is first contact. Here we see this [continental] stuff being produced in its natural habitat," said Bruce D. Marsh, a geologist at Johns Hopkins University. He described the findings at a meeting of the American Geophysical Union in San Francisco.

The ocean floor and volcanic islands such as the Hawaii archipelago are made of basalt, a black rock that in its molten form is the "mother fluid" of the 4.5 billion-year-old Earth. How it gave rise to the silica-enriched rock that formed the continents 2.5 billion years ago is a crucial question in geology.

The geothermal company "recognized immediately that this was something very anomalous," said William Teplow, one of the two geologists at the plant, which generates 20 percent of the electricity used on Hawaii's Big Island.

The chamber is described as being akin to a swollen pancake about the length of a football field and perhaps 50 feet thick. It was hit by chance.

The magma rose about 20 feet up the drill hole before cooling into a glasslike substance. A section of the hole eventually collapsed, pinning the drill tip, which was abandoned along with the final 750 feet of pipe.

Despite that, the discovery is proving to be a lucky strike for Ormat Technologies, a Nevada-based company that operates the Puna Geothermal Venture on the far eastern side of Hawaii's Big Island.

The heat at the bottom of the 8,200-foot hole is two to five times as high as that found in most geothermal projects.

The hole is now in use as an "injection well," through which water and condensed steam is returned to the ground to be re-heated and extracted through "production wells" on the site. The plant generates about 30 megawatts of electricity and is in the process of expanding the output to 38 megawatts.

The continents are made of rock higher in silicon dioxide (SiO2, or silica) than basalt, from which it forms. Most basalt is about 50 percent silica, but continental crusts are about 60 percent silica, and granite has up to 75 percent. Continental rock is formed from magma as relatively silica-poor compounds crystallize out, leaving silica-rich material that solidifies later.