Percolators in the Earth

While chasing a grizzly bear one day in 1847, Explorer-Surveyor William Bell Elliott blundered into a canyon that looked to him like "the gates of Hell." Huge, spiraling columns of steam hissed out of the ground; the earth trembled beneath his feet. "The Geysers," as he named the hill-rimmed valley 85 miles north of San Francisco, is as awesome as ever. But its frightening bursts of steam are now being harnessed. The canyon is the site of the first commercial geothermal-power plant in the U.S., and the installation has paid off so handsomely in eight years of operation that it has set off a small "steam rush" in the Far West.

As old as the earth itself, natural steam is a familiar source of heat and power in countries as widely separated as Italy, Iceland and New Zealand. The renewed interest in the U.S. springs from a growing population's need for more electricity. In some areas, geothermal steam offers a cheap, ready-made alternative to coal, oil and nuclear fuels, and it leaves no pollutants in the air. At The Geysers, steam-driven turbines produce 58,000 kw. of electricity at a cost 23% below that of nearby conventional generating plants; in a few years, the area could be producing almost 20 times as much.

Prospecting for Steam. The largest and most accessible steam fields are located west of the Rockies, where volcanic activity has brought molten, lava-like rock known as magma close to the earth's surface. The 1,500DEG F. magma either releases its own trapped water as steam or, like a gigantic coffee percolator, vaporizes water that has seeped down into the earth.

Occasionally steam emerges through fissures in the ground called fumaroles (from the Latin word fumariolum; meaning smokehole), and the simplest way to prospect for this geothermal energy is to look for such vaporous leaks in the earth's crust. But in areas where the energy remains trapped underground, geologists must use more sophisticated techniques. One method employs infra-red aerial photography. Since the infra-red film is sensitive to heat, geothermal areas are likely to show up lighter in the picture. Another method measures the earth's electrical conductivity, which increases with the presence of subsurface hot water. To tap the subterranean energy, engineers drill with standard oil rigs, going down as little as 600 ft. or as much as 8,000 ft., the depth of the world's deepest steam well at Salton Sea near Brawley, Calif.

The Monster. The job can be dangerous as well as difficult. At The Geysers, a new well erupted with such furious force that the scalded workmen were convinced they had tapped a live volcano. To cool it off, they pumped in cold water until a nearby stream ran dry. Then they tried a concrete plug, without success. "The Monster," as they dubbed the well a decade ago, continues to spout.

Such unrestrained power holds enormous promise. Engineers estimate that by 1980, geothermal energy could be generating as much as 10% of the total electrical output of the U.S. And no matter how much is used, the heat is not likely to be used up. Once scientists master the technology, they should be able to recirculate condensed steam back into the ground, giving virtually unlimited life to wells in states as dry as Nevada. Even without such re-circulation, Italy's 64-year-old Larderello geothermal-power plant near Siena, where fumaroles gave Dante earthly inspiration for his Inferno six centuries ago, is still going strong.

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