WASHINGTON — A geothermal power company drilling a mile and a half deep on the Big Island of Hawai'i 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 the 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 Marsh, a geologist at Johns Hopkins University, who described the findings at a meeting of the American Geophysical Union in San Francisco.

The ocean floor and volcanic islands like Hawai'i 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 key 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 in Puna, which generates 20 percent of the electricity used on the Big Island.

The chamber is described as a swollen pancake about the length of a football field and perhaps 50 feet thick.

The magma rose up about 20 feet into the drill hole before cooling into a glass-like substance. A part 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.

The heat at the bottom of the 8,200-foot hole is two to five times higher than in most geothermal projects.

The hole is now in use as an "injection well" where water and condensed steam is returned to the ground to be re-heated and then extracted through the "production wells" on the site.

Earth's continents are made of rock higher in silicon dioxide (SiO2, or silica) than basalt, from which it forms.

The material that came up the pipe in Hawai'i is dacite, (pronounced day-sight), a translucent substance that is 67 percent silica. It does not exist anywhere on the surface of Hawai'i.

Geologists have previously found silica-rich liquids mixed in with silica-poor solids, and have seen the end product in the form of solid, silica-rich rocks making up continents. What they haven't seen is the intermediate — the molten material in the process of formation.

"Here is a small system, on a scale where we may actually be able to see it happening. This may be how it was with the initial growth of the Earth's crust," Marsh said.