Deep heat: geothermal energy.

In the shadow of Hawaii's Mount Kilauea, the most active volcano on Earth, engineers are building what look like an oil-drilling rig. But instead of hauling up barrels of crude, they hope to tap a cleaner, cheaper, and more plentiful energy source: the same awesome heat that powers the volcano.

Engineers plan to use this geothermal energy to create electrical power for the Hawiian Islands. New forms of energy are important becuase Hawaii doesn't have any of its own oil. Nor does the state have dams large enough to create hydroelectric power, or nuclear power plants. The only way Hawaiians get the energy they need is to import oil or coal from other countries.

The Hawaii Electric Company's idea is not new: Geothermal energy is a major source of power in Northern California, Iceland, and Italy.

But not everyone thinks that a geothermal plant in Hawaii is a good idea. Environmentalist are worried becuase the plant will be smack in the middle of the Wao Kele O Puna rain forest, the largest lowland rain forest left in the U.S. It is home to many unique species of

plants and animals that could be affected by the plant.

Also, many opposed to the plant think that geothermal power is not the best alternative to dirtier and more expensive oil-based power.

LIKE A GIANT EGG

Before you choose sides, look at how geothermal power works.

Think of the Earth as a hardboiled egg--only this egg would be 12,900 kilometers in diameter (see diagrams, pp. 17-18). It has a cool outer "shell" and layers of hotter material buried deep inside.

Geologist call the shell the crust. This thin surface layer is composed of plates of rock much like the pieces of a jigsaw puzzle.

But the crust reaches only 30 to 130 kilometers into the earth. Underneath seethes an inferno. This is the mantle layer, where temperatures can reach more than 1,371 [degrees] c, hot enough to melt rock that can extend down to more than 3,200 kilometers. Geologists call the melted rock magma.

Great pressures can sometimes force magma up to the surface via cracks between the plates of the brittle crust layer. This is how volcanoes form. They spew out the molten rocks as hot flowing lava.

There's other evidence for the great heat deep under our feet. You've probably heard of Old Faithful, the famous geyser at the Yellowstone National park. This and other geysers result when rainwater and melted snow trickle

down through cracks in the crust to. form an underground reservoir. If the reservior lies near a pool of molten magma, the water gets so hot that it regularly explodes as a burst of steam--a geyser. A similar process creates the many natural hot springs near geysers and volcanic mountains.

How to tap this explosive source of energy? First, engineers drill a deep well into a layer of porous rock sitting above a pool of magma. Hot water or stream is often trapped in these "holey" rocks.

When the well taps into a reservoir, hot water and stream rise to the surface. Here the stream enters pipes, which carry it under enormous pressure to a machine called a turbine. The pressurized steam turns a wheel the same way blowing on a pinwheel sends it spinning. The turbine powers a generator which converts the mechanical (spinning) energy into electricity. The electric current then travels down power lines to homes and businesses.

When we use coal or oil to make electric power, we burn the fuel to boil water to create the steam that spins turbines. Since geothermal plants use steam directly from the ground, several steps, lots of money, and much of the pollution are eliminated.

NOTHING 'S PERFECT

But geothermal energy does have some drawbacks. These are just some of them:

* In addition to hot water and steam, geothermal wells release hydrogen sulfide and sulf-dioxode gases from underground. Besides being poisonous, the gases "smell disgusting, like rotten eggs," says Sierra Club Representative Barbara Boyle, a leading critic of the plant. Gas emissions from the Kilauea test well have already forced farmers to evacuate the area three times.

* The underground water used to power geothermal plants contains toxic substances, such as boron, ammonia, and mercury. Geothermal water can even be radioactive. Dumping the used water on the ground or in rivers could kill many forms of life.

* The land around a geothermal well often sinks after large amounts of fluid are removed.

* Geothermal plants can be quite noisy as pressurized steam rushes up narrow wells.

* Some Hawaiians who view the volcano as scared oppose the geothermal plant at Kilauea for religious reasons.

CLEANING UP THEIR ACT

Those in favor of geothermal power say they can address these concerns with modern technology. For example, industrial scrubbers can keep harmful gases from escaping into the atmosphere. Waste water can be reinjected into the well to help replenish the reservoir, eliminate pollution, and prevent land sinkage.

The Hawaii Electric Company also says that it will need only about 300 of the approximately 30,000 acres of the Puna rain forest for its plant. But rain forest activists maintain that roads required by the plant will allow "foreign" plant species to migrate into the forest (seeds travel well in the treads of car tires), thus destroying the unique character of the forest.

Instead of geothermal energy, the environmentalists say that Hawaii should look to conservation and other forms of renewable energy to meet its growing needs. "If any place could make a go of solar or wind power, it's Hawaii," says the Sierra Club's Boyle, referring to the state's bounty of sunshine and offshore winds.

PARKS VS. ENERGY

Battles similar to the one being fought in Hawaii are also being waged on the borders of two national parks: yellowstone in Wyoming and Carter Lake in Oregon. Power companies there want to tap into Earth's heat deep under each park, so they've leased land on the park borders

Not only are environmentalists worried about having ugly power plants so close to such beautiful areas, but some geologists say that tapping into nearby geothermal reservoirs could shut off Yellowtone's geysers and possibly spoil the famous clarity of Carter Lake.

The choice is a different one: Do we allow some development in these pristine areas so we don't have to pollute our atmosphere with coal and oil, or do we continue to search for better energy alternatives? What do you think?