According to Māori tradition, the legendary priest Ngātoroirangi holds the distinction of being the first person to ever bathe in a hot spring. Rather than a relaxing stress-reducer, for Ngātoroirangi, the hot spring was a matter of survival.

Caught in a blizzard and rapidly freezing to death, Ngātoroirangi cried out for his sisters, asking them to bring sacred fire from their homeland of Hawaiki to warm him up. They obliged, coming to Ngātoroirangi’s aid by carrying baskets of fire through an underground passage. Wherever Ngātoroirangi’s sisters surfaced along the way, the sacred fire formed volcanoes and hot springs. The warmth of one of those hot springs saved Ngātoroirangi’s life.¹

It’s a fitting creation story. A warm bath prepared by the earth itself sounds downright mythic, but the Māori legend also reflects some stunning facts about the close association between hot springs and life itself. The recent discovery of stromatolites, a type of rock produced by photosynthesizing bacteria, in a 3.5-billion-year-old geothermal hot spot in Western Australia suggests life on Earth may have begun in a hot spring.²

People and animals alike have been attracted to these geological curiosities since time immemorial, and many cultures have woven tales of their mystical natures and miraculous healing properties. Many of the indigenous people of North America considered hot springs to be so sacred that warring tribes would temporarily suspend hostilities in the vicinity of a hot spring.³

Again, the folklore isn’t far from the facts. Thanks to the burgeoning field of balneology, the study of the medical applications of bathing, we have scientific evidence to support the healing power of hot springs. The heat and water pressure of a hot spring work in tandem to block pain receptors, dulling any aches a bather may have. The higher mineral concentration of the water makes a person more buoyant as well, which relieves strain on joints and muscles. One study even found soaking in a hot spring could possibly combat the symptoms of chronic heart failure.⁴

Plus, a long soak in a nice warm bath just makes you feel good. Everyone knows that — when it comes to bubble baths we'll take folklore over science.

What everyone might not know is that geothermal energy — the energy which keeps a hot spring hot — has power far beyond physical and mental healing. It could even help literally heal the world.

Is It Hot in Here?

Before we can talk about the practical applications of geothermal energy, we first have to understand the architecture of the earth itself. At the planet’s core is a solid ball of iron some 1,500 miles in diameter. Surrounding that inner core is an outer core composed of magma. Above the outer core is the earth’s mantle, a mixture of magma and solid rock. Binding it all together is the crust, the planetary surface on which we all live.⁵

Thanks to the force of gravity, the three overlying layers bear down heavily on the earth’s inner core, and that pressure gets transformed into heat energy. Meanwhile, radioactive materials are constantly decaying in the core, releasing even more heat. In addition to all that, the core also contains residual heat from the initial formation of the planet, when the rapid accumulation and condensation of matter generated incredible amounts of energy. Take that all into account, and you shouldn’t be too surprised to learn the earth’s inner core reaches a scorching 10,800 degrees Fahrenheit — as hot as the surface of the sun.⁶

This, the heart energy of the earth, is geothermal energy, an estimated 42 million megawatts of which constantly flows from the earth’s core up to the surface. To put that in perspective, a single megawatt can power about 164 homes for an hour.⁸ Or in other words, there is enough energy flowing to power all the homes on earth comfortably.⁷

Usually, by the time that heat has reached the surface, much of it has dissipated. Sometimes, however, the heat takes a more direct route. It may erupt as magma from a volcano, or as hot gas from a fumarole. It may burst out of a geyser, or it might (if we’re lucky) become a hot spring.

Like any other spring, a hot spring is ground water welling up to the surface — but with one key difference. This water is heated by geothermal energy. Some hot springs are heated by volcanic activity, but not all are. If groundwater penetrates deep enough below the earth’s surface, it will pick up some of that heat radiating from the core, regardless of whether or not there’s a volcano around. When the water moves back up to the surface too quickly to cool down, you end up with a hot spring.⁹

We Could Power the Whole World

The planet’s core constantly produces heat and vents it to the surface, which means all of us are walking around on what is essentially one big self-sufficient “heat engine,” according to Earth scientist William Glassley. In his estimation, “There is enough heat constantly available [below the earth’s surface] to generate sufficient power to supply the entire world.”¹⁰

And geothermal energy is not just renewable, but also much cleaner than most other energy sources. Geothermal power plants emit 99 percent less carbon dioxide than comparable fossil fuel power plants because, instead of burning fuel to generate electricity, they use steam and water, much of which is returned to the earth for future geothermal use.¹¹

The most common type of geothermal power plant, called a “flash steam plant,” converts hot water from a geothermal reservoir into steam, which then powers turbines to generate electricity. When the steam condenses back into water, it is recycled into the ground to be used again. On the other hand, a “dry steam plant” uses the steam directly produced by a geothermal reservoir to move the turbines.¹²

While both types of power plants are feats of engineering, their designs also hint at one of the major stumbling blocks preventing wider usage of geothermal energy. Both dry steam and flash steam plants must be located near sufficiently energy-rich geothermal reservoirs. While geothermal energy is plentiful, it doesn’t always take the form of hot water and steam that’s ready to power a turbine.

However, a third type of geothermal power plant is quickly becoming the most common type because it can harness lower-energy spots the other plants cannot. A “binary cycle plant” uses hot geothermal water to heat a second liquid, which then turns to steam that powers the turbines. That may sound needlessly complicated, but consider it this way: The water in a geothermal reservoir may not be hot enough to turn into steam on its own, but it could be hot enough to turn another liquid with a lower boiling point into steam. In this way, binary cycle plants allow us to tap a wider range of geothermal reservoirs. They are also closed systems, which means their emissions are even lower than those of other geothermal plants.¹³

Geothermal energy can also be used more directly to heat homes. In Reykjavík, Iceland, 95 percent of the buildings are heated with water pumped from geothermal wells, making it one of the cleanest cities in the world.¹⁴

Of course, Icelanders have it relatively easy: Accessible geothermal wells abound on the island. However, even in areas without constant volcanic activity, geothermal heat pumps can heat a home more cleanly, efficiently, and cost-effectively than alternatives like natural gas and oil. These heat pumps use systems of pipes containing high-pressure refrigerants to draw heat from underground, where the temperature tends to stay at a steady 50 degrees all year long thanks to the energy rising from the earth’s core. To cool a home, the heat pump reverses the procedure, disbursing excess heat from the home directly into the ground. Whereas a standard heat pump would consume about 2.2 kilowatt-hours of energy to produce 12,000 BTUs of cooling or heating energy, a geothermal heat pump needs less than half that amount to produce the same level of energy.¹⁵

Geothermal Cuisine (Yes, It’s a Thing!)

As the complex dynamics of geothermal power plants and heat pumps attest, people have long looked for ways to put hot springs to use beyond bath time.

Icelanders have also found a more unexpected use for their hot springs: baking. Hverabrauð, or “hot spring bread,” is a dense rye loaf made by mixing up a typical bread dough and then burying it near a hot spring. The geothermal heat bakes the dough, and about a day later, you can dig up a fully cooked loaf.¹⁶

But Icelanders are not the only people to have ever realized you could cook with a hot spring. For example, the Māori people would seal food in flax bags and lower it directly into the springs.¹⁷ They also use a method known as hāngi, in which starches and meats are cooked on hot stones. Some Māori chefs use fire to heat their stones, but others use natural hot springs to do the trick.¹⁸

Meanwhile, in Pagosa Springs, Colorado, the Geothermal Greenhouse Partnership (GGP) is pioneering a new approach to year-round farming with, as you might have guessed, geothermal greenhouses. The system works like so: Geothermal water heats domestic water, which is then pumped through a system of pipes to heat the greenhouse during the colder months. This allows the greenhouse to maintain consistent, produce-friendly temperatures all year long. Given that the average growing season in the area is roughly 80 days, this is a major achievement. Because the geothermal water is not used to heat the building directly, the system is a closed loop. The vast majority of the water can be returned to the ground, uncontaminated by any waste the greenhouse might produce.¹⁹

The GGP’s geothermal greenhouses have wide implications for sustainable farming around the world, and they’re also positive community resources. The GGP plans to invite food banks and other community groups to grow their own produce in its greenhouses, and the GGP has given some of its own vegetables to free food programs for children in need. Local students regularly take field trips to the GGP’s greenhouses to learn about science, math, and engineering in a hands-on learning environment.²⁰

“It’s this living laboratory that we have right smack in the middle of town,” says Cindy Schultz, an associate planner with the town of Pagosa Springs. “It gives people a sense of what’s possible.”²¹

That sense of possibility is just as valuable as the other, more material benefits of the GGP’s project. The wider adoption of geothermal energy could help us significantly cut fossil fuel consumption — but unfortunately, there are some obstacles in the way. To get over those hurdles, we’ll need the courage to imagine alternatives like those represented by the GGP.

Who’s Afraid of Geothermal Energy?

Despite the clear benefits of geothermal energy — and the fact that geothermal power plants have been around in some form since 1904 — its use is still limited.²² The U.S. is the world leader in geothermal energy production, generating 16.7 billion kilowatt hours every year. That number sounds big, but it only accounts for 0.4 percent of U.S. electricity production.

Other countries produce less total geothermal energy, but use more relative to their electricity consumption. For example, Kenya is the world’s eighth largest producer, but the country gets 44 percent of its total power from geothermal.²³ All told, 23 countries generate geothermal electricity of some kind, but researchers believe we’ve only unlocked 6-7 percent of the planet’s potential geothermal resources.²⁴

As mentioned above, binary cycle plants can help us harness more geothermal energy, but they don’t solve all the problems. Fossil fuels are more energy rich than geothermal reservoirs, and thus, a more efficient way of producing energy — in the short term, that is. The long-term consequences of fossil fuels, as we’ve learned, are anything but efficient.²⁵

Funding, too, poses a challenge. It is often harder to get funding for a geothermal plant precisely because other, less sustainable forms of energy require fewer resources to mine and monetize. As a result, the upfront costs of building a geothermal plant can be prohibitively high.²⁶

Still there is reason to be optimistic. Scientists like Glassley believe further technological developments will eventually overcome all geographical limitations to geothermal energy production and make the process more cost-effective.²⁷

Such a day is likely decades away at the moment, but in the near term, the price of geothermal energy has been falling. That’s thanks in part to tax incentives and government mandates for renewable energy.²⁸ According to the Congressional Research Service, financial incentives for renewable energy accounted for 65.2 percent of all federal tax-related support for the energy sector in 2017, whereas only 25.8 percent of tax-related support went to the fossil fuel industry.²⁹

That’s a heartening trend, but we can only count on it to continue if we, as a public, make it clear that renewable energy is what we want. The U.S.’s current presidential administration has repeatedly attempted to end subsidies for renewables.³⁰ Curtailed government financial support could hamper necessary efforts to further develop geothermal technology.

Which is not to say that only doom and gloom await the nascent geothermal energy industry. Rather, as with other efforts to create more sustainable ways of living, we all need to pitch in however we can, whether that means supporting local geothermal projects or calling our representatives to voice our concerns.

One of the world’s most powerful renewable energy resources is the world itself. We just need to direct our own energy and imagination to use it.

— The Keap Team