Tom Roush, age 12, of Roy, Wash., for his question:

WHERE DOES GEOTHERMAL ENERGY COME FROM?

The word geothermal reveals its identity when we take it apart. Geo refers to the earth and thermal means heat. Hence, geothermal energy must be heat energy that comes from the earth. The whole thing is a fascinating story, full of promises to help to tide us over our present energy crisis—until we learn how to harness solar energy.

We are told that the earth is warmed by the fiery furnaces of the sun. This is true. But the earth also has enormous supplies of its own heat, most of it stored down in the interior, far below the cool, rocky crust. Scientists suspect some of this internal planetary heat comes from heavy radioactive substances, perhaps in the core. Some is caused by the pressure of weighty crustal layers.

This internal heat is called geothermal energy, especially when it is close enough to the surface to be usable. As a rule, these usable pockets are in regions where fairly recent volcanic activity left lingering heat within the crust. There it makes itself known when it comes in contact with seeping ground water, creating hot springs, steamy geysers and smoky fumaroles. This heat can be used as a source of energy. People use this geothermal energy in Iceland and New Zealand, where hot springs and geysers abound.

The idea is not new. But modern scientists tell us that the earth can give us far more of this free, nonpolluting energy. Most of it however, is at deeper levels where hot lava once intruded between buried crustal layers. This heat may remain stored there for thousands of years. All we have to do is to reach down and help ourselves.

There are several ways to do this though all of them use water, which is nature’s own method of bringing buried heat to the surface. This works in a rather wondrous way because, under pressure from above, ground water remains liquid at far higher temperatures than its normal boiling point.

Geysers and fumaroles escape through natural vents. This removes the pressure and the superheated water turns to steamy vapor. The same thing happens in a man made geothermal plant. Various plumbing systems drill down to the hot level and presto, the superheated water provides steam to spin the turbines of electric generators. Surveys reveal numerous pockets of geothermal energy at reachable depths, especially in our western mountains where a few plants already provide electric power. Geologists suspect that the earth has enough of this wondrous energy to supply our needs for many centuries.