Carbon dioxide could explain how geysers spout

Yellowstone National Park, in the western United States, holds more geysers than any place else in the world. For 150 years, scientists have blamed hot water alone for fueling those spectacular watery eruptions. But scientists have been monitoring the innards of these gurgling geysers. And it’s not the hot water alone that’s making them spurt into the air like a fountain. Carbonation helps the geysers erupt — like shaken cans of soda pop, they now report.

Yellowstone sits atop an ancient volcanic hot spot. In the past, that hot spot has spouted massive eruptions of magma. Today, though, all that erupts is water in the form of geysers.

One group of researchers monitored eruptions of Yellowstone’s Spouter geyser. During the buildup to an eruption, carbon-dioxide (CO₂) gas accumulates in its water. The researchers reported that finding online March 7 in Geology.

The dissolved gas lowers the water’s boiling point. And that’s what triggers an eruption, they say. This phenomenon may occur elsewhere in Yellowstone. Several of the park’s other geysers, including Old Faithful, also contain abundant carbon dioxide and other dissolved gases. That study, by a separate research team, appears in the March issue of Geology.

“People always assumed that water was the end of the story,” says Jacob Lowenstern. He is a volcanologist with the U.S. Geological Survey in Menlo Park, Calif., who was not involved in either study. “If CO₂ was completely absent, many of these geysers would still erupt. But they erupt more regularly and frequently because of the dissolved CO₂ gas,” he now says.

Geysers can spew thousands of liters (gallons) of water tens of meters (yards) into the air. For geysers in Yellowstone National Park, the heat from underground magma fuels these spritzers. Measurements in the 1970s, however, revealed that many Yellowstone geysers aren’t hot enough to boil pure water.

Uncovering what is going on inside Yellowstone’s geysers has proven difficult.

Geyser water is scorching hot and often acidic. Bethany Ladd and Cathryn Ryan are authors of the March 7 study. These geologists work at the University of Calgary in Canada. They lost equipment to these harsh conditions while attempting to monitor several of Yellowstone’s geysers.

The researchers had better luck at the nonacidic Spouter . Using special glass jars, the researchers sampled the geyser’s water every 10 to 20 minutes. They collected the water from a side vent that branches off the geyser’s main channel. These measurements allowed the researchers to track how much dissolved CO₂ was in the water during several eruptions.

CO₂ levels start low, the researchers found. During the one- to two-hour interval between eruptions, however, CO₂ levels steadily rise. That is when gases from Yellowstone’s magma enter the geyser water through permeable rocks.

As CO₂ increases, this gas lowers the water’s boiling point. Eventually the boiling point drops below the water’s actual temperature and bubbles of steam and CO₂ form. As these bubbles climb up through the geyser column toward the surface, they expand. They now displace water and lower the pressure inside the geyser. That pressure drop lowers the boiling point even further. And that sparks a runaway reaction that triggers a full-blown eruption similar to that of a shaken can of soda pop.

These eruptions can last for hours. By the time the eruption finally fizzles, CO₂ levels in the water will have dropped to about half of what their peak value had been just before the eruption.

Now the cycle begins anew.

“People typically think of geysers as hot-water features that only emit water and steam,” Ladd says. “But there are other things in the water such as CO₂ that have huge implications for geyser eruptions.”

Shaul Hurwitz is a geologist at the U.S. Geological Survey in Menlo Park. In a second new study, he and his colleagues discovered CO₂ and other dissolved gases such as nitrogen in many of Yellowstone’s geysers.

Understanding the role that gases plays in steam eruptions is important, Hurwitz says. That’s because geysers aren’t the only way water erupts. The rapid boiling of an enclosed, underground water reservoir can generate an explosive blast. In September 2014, for example, a steam eruption rocked Japan’s Mount Ontake volcano without warning. It killed 57 people. If CO₂ helps fuel steam eruptions, then monitoring gas levels in groundwater could provide early warning, Hurwitz says.

Power Words

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acid    A chemical that releases hydrogen ions when dissolved in a solution. Acids have a sour taste and have a pH ranking of less than 7.0.

acidic   An adjective for materials that contain acid. These materials often are capable of eating away at some minerals such as carbonate, or preventing their formation in the first place.

carbonation    The process of pumping carbon dioxide into a liquid, to imbue that liquid with bubbles. It gives the now-carbonated liquid a fizzy taste.

carbon dioxide (or CO₂)   A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

dissolve    To turn a solid into a liquid and disperse it into that starting liquid. For instance, sugar or salt crystals (solids) will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.

geology   The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

geyser     A vent (opening) in Earth’s surface that intermittently sends up a tall spray of steam or hot water. The sometimes explosive discharge of water and steam is propelled by the geothermal heating of water below ground.

groundwater   Water that is held underground in the soil or in pores and crevices in rock.

implicate      (n. implication) To confirm or conclude that one thing is involved in another.

magma    The molten rock that resides under Earth’s crust. When it erupts from a volcano, this material is referred to as lava.

nitrogen    A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth’s atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.

permeable    Having pores or openings that permit liquids or gases to pass through. Sometimes materials can be permeable for one particular type of liquid or gas (water, for example) but block others (such as oil).

phenomenon    Something that is surprising or unusual.

pressure   Force applied uniformly over a surface, measured as force per unit of area.

reservoir    A large store of something. Lakes are reservoirs that hold water. People who study infections refer to the environment in which germs can survive safely (such as the bodies of birds or pigs) as living reservoirs.

volcanism     The processes by which volcanoes form and change over time. Scientists who study this are known as volcanologists and their field of science is known as volcanology.