Roles for Fumaroies

Anyone watching a geyser, hot spring or fumarole (volcanic steam jet) in the U.S. West may well wonder why the earth's hot interior is not used as a source of energy, in the manner of volcanic steam power plants in central Italy. Last week Pacific Gas & Electric Co. of California announced that it has struck a deal to make electricity out of underground steam produced jointly by Magma Power Co. of Los Angeles and Thermal Power Co. of San Francisco.

The site of the earth-power plant will be a hot spot near Healdsburg, 60 miles north of San Francisco, where hot springs and fumaroles abound. President Barkman C. McCabe of Magma Power thinks that a crack in the earth's crust allowed magma from the earth's hot interior to rise fairly near the surface. Magma is uneasy stuff, an intensely hot solution of steam and other gases in melted rock. When it bursts out in large quantities, it builds a volcano. When it does not quite break loose, it creates a geothermal area like the place near Healdsburg.

Atop their near-volcano, Magma Power and Thermal Power drilled four steam wells, using ordinary oil-well drilling equipment. The wells are 500 to 700 ft. deep, and the temperature -of the rock at bottom is about 600DEG F. When the wells are capped, steam pressure measures 300 to 400 Ibs. per sq. in., but when the steam flows, pressure drops to 100 Ibs. and temperature to 384DEG F.

Part of the water in the steam, says McCabe, is "juvenile water" which comes out of the magma or the rock around it. The rest is rain water that seeps into the ground and turns to steam when it reaches hot rock. The steam contains less than 1% of noncondensable gases, mostly carbon dioxide, and no corrosive minerals. For the time being, Pacific Gas & Electric Co. will be content with a 12,500-kw. generator, but much more steam may be available. Wells drilled 30 years ago and abandoned as uneconomic have been spouting steam ever since with no loss of pressure. "Neither we nor anyone else," says McCabe, "know whether we are looking at an area that will produce 50,000 or 5,000,000 kilowatts."

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