How Geysers Work

Imagine taking all of the water from your neighborhood swimming pool, pouring it into a massive, magma-powered pressure cooker and shooting the water hundreds of feet in the air. Geysers like Old Faithful create eruptions of this scale every day, to the delight of the millions of visitors who witness them each year. Yet, despite the unbelievable forces that drive their eruptions, geysers are among the rarest and most fragile natural phenomena on Earth. Landslides, earthquakes and many other factors can alter a geyser's eruptions or destroy the geyser altogether. What's more, nature isn't the only thing that can impact a geyser: Man has helped to destroy numerous geysers as well, sometimes unintentionally and sometimes through deliberate acts of vandalism.

As of 2009, there are only about a thousand geysers left active on the planet, in geyser fields in such diverse locales as Iceland, New Zealand, Chile and the U.S. [source: Glennon]. The one thing all of these locations have in common with one another is a high level of geothermal activity, one of the key components of geyser formations. Geothermal energy, which is taken from heat within the Earth, drives volcanoes, hot springs and other forms of geothermal activity. Still, a geothermal energy source is just one necessary part of a typical geyser formation.

In this article, we'll explore what else it takes to form a geyser, what exactly causes one to erupt and what makes some geysers so unique. Along the way, we'll also take a look at some springs that look and act like geysers, but operate in a completely different way.

How Geysers Form and Erupt

In addition to a heat source, geysers need a constant supply of water and an underground plumbing system that holds the water supply as it heats up. We'll examine each of these separately and then explore how they work together to cause geysers to erupt.

Water supply: Clearly, a geyser needs a water supply. What might not be so apparent, however, is where the water in a geyser's eruption comes from. The answer depends on the geyser. Many geysers are located near rivers and pull water from them. Others seem to depend more on rain and snow filtering miles beneath the ground for their water supply.
Plumbing system: A geyser's plumbing system is a series of fissures in the Earth that start at the geyser's mouth and run miles beneath the Earth's surface, where the system connects to the geyser's heat source. Each geyser's plumbing system is different: Some consist of a single long, vertical shaft, while others connect to large pockets of water beneath the surface. Certain types of soil are much more suitable for the plumbing system's formation, particularly soils that contain a high concentration of rhyolite, a volcanic rock that contains minerals that seal the geyser's plumbing system [source: National Park Service]. This mineral lining is crucial to the geyser's formation, as geysers operate under tremendous pressure and the plumbing system must be able to contain this pressure for the geyser to function.
Heat source: We already know that geysers occur in areas of high geothermal activity, but where does that energy come from? The water in geysers is heated by magma that lies around 3 miles (4.8 kilometers) beneath the surface of the Earth. While that might seem like a long way down, magma underneath a geyser field is actually relatively close to the Earth's surface. There are different reasons why the magma is so close to the Earth's surface, though many geyser fields are located on the edges of the Earth's tectonic plates. These plates, which compose the Earth's lithosphere, are constantly in motion, creating faults and generating tremendous energy. This activity can cause earthquakes and volcanoes, and it can also create heat sources for geysers.

In the next section, we'll learn why the boiling point of water is so critical to understanding how a geyser erupts.

How Do Geysers Erupt?

Now that we understand how the key components of a geyser work, let's figure out how these parts work together to create such spectacular eruptions.

The process begins as water migrates to the geyser's plumbing system through fissures in ground. Since the plumbing system is miles deep, the water at the bottom of the geyser's plumbing is under incredible pressure from the water above it. Think of the entire system as a giant pressure cooker.

Pressure cookers work by creating a sealed, pressurized enclosure that helps to cook food much faster than cooking it in a normal pot. Pressure cookers can do this because water's boiling point rises as it's pressurized. Think of what actually happens when water boils: Water starts to churn and bubbles of air begin to surface. If more pressure pushes down on the water, water needs more and more energy (in the form of heat) to overcome that pressure and start pushing bubbles to the surface. This explains why water inside a pressure cooker can reach temperatures of more than 125 degrees Celsius (257 degrees Fahrenheit), while the boiling point of water at standard pressure is only 100 degrees Celsius (212 degrees Fahrenheit).

Now consider the massive pressures placed on water within a geyser's plumbing system. Water in such a system can reach incredibly high temperatures (and store incredible amounts of energy as a result) before it starts to boil. As the magma at the base of the geyser transfers heat throughout the system, more energy gets trapped in the water. Eventually, pockets of water begin to reach their boiling point and become turbulent. This turbulence pushes a relatively small quantity of water out of the opening of the geyser, decreasing the amount of pressure on the water remaining in the geyser. With this sudden pressure drop (and corresponding drop in boiling point), the water in the geyser flashes into steam. The steam quickly expands to 1,500 times the volume of water and this expansion violently pushes water and steam from the mouth of the geyser in an eruption. These eruptions last as long as the water in the geyser remains hot enough to push water out of the geyser opening. Eventually, the entire system will either run out of water or the water will cool down enough for the eruption to stop. The cycle, of course, starts all over again.

Exploring the World's Most Famous Geysers

While every geyser operates in fundamentally the same way, all geysers are not created equal. In this section, we'll explore some of the world's most famous geysers and what makes them stand out above the rest.

Geysir: This geyser, located in Iceland's Haukadalur valley, was first discovered in 1294, making the Geysir the oldest known geyser on the planet. Geysir's activity slowed toward the end of the 19th century and it became dormant around 1915. In 1935, however, an earthquake reactivated the geyser, which currently erupts about every eight to 10 hours. Geysir remains a major tourist attraction to this day [source: Geysir Center].
Old Faithful: Probably the most famous geyser on Earth, Old Faithful is famous for its 100- to 180-foot (30 to 55 meter) high eruptions, as well as for the regularity with which these eruptions occur (hence the name). The geyser takes about 45 to 110 minutes between eruptions, though more recently, its eruptions have tended to be larger and consequently farther apart as more water is needed to replenish the geyser [source: National Park Service]. Old Faithful is also a great example of a cone geyser. Unlike fountain geysers, which erupt from a pool of water, cone geysers erupt from a cone shaped structure formed from the mineral-rich water that constantly shoots from its opening [source: National Park Service].
Grand Geyser: The tallest regularly erupting geyser on Earth, Grand Geyser routinely fires water up to 200 feet (61 meters) into the air. Located in Yellowstone National Park, Grand Geyser is a great example of a fountain geyser. Unlike cone geysers, which tend to produce a fairly vertical, constant column of water, fountain geysers erupt in a much more chaotic fashion [source: National Park Service].
Strokkur Geyser: This geyser, named after the Icelandic verb "to churn," is known for its frequent eruptions, which occur five to 10 minutes apart. First active in 1789, Strokkur became inactive in 1896 after an earthquake hit the area and blocked its plumbing system. In 1963, locals cleared the blockage and the geyser has remained active ever since [source: Geysir Center].
Steamboat Geyser: Don't bother waiting for one of Steamboat's massive eruptions. While Steamboat is considered to be the world's tallest active geyser, shooting water up to 300 feet (91 meters) in the air, the geyser is also notoriously finicky. At one point, the geyser went 50 years without an eruption.
Waimangu Geyser: The highest geyser eruption of all time took place at New Zealand's Waimangu Valley. In 1902, a geyser in the valley reportedly spouted water 1,475 feet (450 meters) in the air. Unfortunately, the geyser became inactive after a landslide in 1904, putting a premature end to a truly spectacular sight [source: Geyser Grazing Society].

Human Interaction with Geysers

Now that we've taken a comprehensive look at how geysers work, we're ready to look at man's past and present interaction with them.

Considering the spectacle of a geyser eruption, it's no surprise that tourism is the most common way that people interact with geysers. Tourism serves to educate the public both on how geysers work and on what it takes to protect these natural resources. Parks often take great care to control how tourists interact with geysers, in part because tourists can harm geysers with their trash and debris, but also because geysers are quite capable of harming tourists as well: In 1903, four tourists visiting New Zealand got caught in a geyser jet in Waimangu Valley. The eruption killed all four people and carried them more than a mile (1.6 kilometers) away from its source [source: Geyser Grazing Society]. While such incidents are rare, we should always remain conscious of the amazing forces behind geysers.

Geysers serve as more than tourist attractions, however. The same geothermal energy that drives geyser activity can also be used to generate power for houses and businesses. While geothermal energy can provide a clean source of electricity, tapping into that source can sometimes create major consequences for geothermal features in the area by draining the geyser fields of their water or energy.

People have also been known to intentionally destroy geysers through vandalism, throwing trash and debris into a geyser's opening and blocking its plumbing system. It's somewhat ironic, then, that man has also gone to great lengths to create "artificial" geysers by digging wells that tap into a geothermal heat source. While that type of geyser has a man-made plumbing system, its eruptions are driven by the same forces that power its natural counterparts. People have also put a lot of energy into repairing natural geysers, as in the case of Iceland's Strokkur Geyser.

As we understand more about how fragile geysers are, we'll see more measures put in place to protect these natural wonders. If you're interested in learning more about geysers, take a look at the links on the following page.

How Geysers Work

How Geysers Form and Erupt

How Do Geysers Erupt?

Exploring the World's Most Famous Geysers

Human Interaction with Geysers

Lots More Information

Related HowStuffWorks Articles

More Great Links