GEOTHERMAL ENERGY

In purest theory, this method alone could supply mankind with all the energy it needs for millenia; but the fact is that at present geothermal energy supplies only about 1,000 MW in the whole world by harnessing natural underground steam in California, Mexico, New Zealand, Italy and a few other places where it has been found.

The difficulties are many, lack of exploration, corrosion of machinery by salty water (AtE Mar.75), and lack of experience with the "dry" method, for example. In the last case, there are also fears that the cracks in the hot rock could be plugged by the corrosive water at high temperature and pressure, and the steam would be blocked.

That fear is unfounded, at least if the geochemistry is favorable, says Prof. W.F. Libby of the U. of

Calif. at Los Angeles. He has produced evidence that much of the steam used by power plants in California's Geysers geothermal field is generated from rainwater of recent origin.

Prof. Libby examined the radiological records of natural water made shortly after nuclear weapons tests in the atmosphere in March 1954. There was a 50-fold increase of tritium (an isotope of hydrogen) in the rain falling on Chicago and elsewhere in the Northern hemisphere, tagging this rainwater with a "tracer." Samples of water taken at the Geysers shortly after this abrupt increase revealed that about l0% of the hot water was rainwater less than two weeks old, and the conclusion was confirmed by checking the records at four hot springs in Nevada.

"It therefore seems likely to me," writes Libby in a recent letter to Science, "that this 'dry' geothermal method, with its enormous potential, must be feasible."