How do geysers work? Knowledge gained from two centuries of scientific research and observations

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Shaul Hurwitz, Research Hydrologist with the U.S. Geological Survey, and Michael Manga, Professor of Earth and Planetary Science at the University of California, Berkeley.

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The English word geyser is derived from Geysir, a name given by Icelanders in the seventeenth century to an intermittently discharging hot spring in southwest Iceland. Geyser-like behavior in natural systems has also been observed on the ocean floor and is inferred to occur on Saturn's moon Enceladus and Neptune's moon Triton.

Natural geysers on Earth are not common; there are fewer than 1,000 worldwide, and about half of these are in Yellowstone National Park. Other large geyser fields in the world include the Valley of Geysers, in the Kamchatka Peninsula in Russia; El Tatio, in the northern Chilean Andes; Geyser Flat, Whakarewarewa in the Taupo Volcanic Zone in New Zealand; and the shores of Lake Bogoria in Kenya. These geysers are sensitive to environmental changes. In fact, most of the geysers in the Taupo Volcanic Zone and many that were present in Nevada have vanished due to geothermal energy production.

Geysers attract researchers from multiple disciplines in part because they provide natural laboratories to study processes that may be similar to those operating in volcanoes. Geysers also provide an opportunity to measure geophysical signals before, during, and after repeated eruptions. An improved understanding of geyser behavior may yield insight into other intermittent processes in nature that result from localized input of energy and mass, and is also critical for the preservation of these spectacular natural phenomena, so that humans do not influence their activity.

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Written documents describing scientific measurements and models of geyser eruptions date back to the nineteenth century. In addition, much of the knowledge about various aspects of geyser activity comes from visual observations made by park rangers and enthusiasts, such as members of the Geyser Observation and Study Association (GOSA). Through monitoring eruption intervals, analyzing geophysical data, taking measurements and making observations within geyser conduits, performing mathematical computer simulations, and constructing laboratory models, some fundamental questions about geysers have been addressed:

1. geysers are uncommon because they require a combination of heat from recently active magmatic systems, water, and geological deposits with abundant fracture networks. Together, these features create reservoirs that allow hot water to accumulate and then be discharged in discrete events.
2. the major geyser fields on Earth were formed following the last glaciation (<14,000 years ago).
3. geysers are transient features with periods of activity and dormancy. They are affected by earthquakes, landslides, changes in water recharge rates, erosion of their cones or mounds, and slow silica deposition in flow channels and reservoirs.
4. many geysers appear to have some form of subsurface reservoir that allows steam to accumulate between eruptions. The ascent and eruption of water unload the geyser conduit and deeper reservoir and promote boiling beneath the ground.
5. carbon dioxide dissolved in thermal waters could affect geyser eruptions.
6. deep and large reservoirs provide more water, hence creating larger and longer eruptions. Regularity of geyser eruptions is promoted by reservoirs that are deep enough that they do not sense surface weather changes and large enough that external forces (like earthquakes) are of little consequence. As these reservoirs are well below the surface and are large, most geysers are not particularly sensitive to weather changes at Earth's surface. Pool geysers, however, in which the volume of water that must be heated is in contact with the atmosphere, are most sensitive to surficial factors such as changes in wind speed and air temperature.
7. geysers can influence each other, and so hydraulically isolated geysers (like Old Faithful) tend to be more regular in terms of eruption recurrence.

Two centuries of scientific research have significantly improved the understanding of "how geysers work." However, almost a century and a half after the geological survey led by Ferdinand V. Hayden in what would later become Yellowstone National Park, one of his conclusions still remains pertinent: "What remains to be done is to start a series of close and detailed observations protracted through a number of consecutive years, with a view to determine, if possible, the laws governing geyseric action".

More information on geyser research can be found in a recent review article titled "The Fascinating and Complex Dynamics of Geyser Eruptions" published in the Annual Review of Earth and Planetary Sciences and in a short video from Knowable Magazine (https://www.youtube.com/watch?v=5pOkXBxI6Do).