The Complex Dynamics of Geyser Eruptions

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Despite two centuries of scientific study, basic questions persist about geysers—why do they exist? What determines their behavior?

boiling water and white steam blasting up out of erupting geyser with snow on the ground
Old Faithful Geyser erupts on a clear winter day in Yellowstone National Park (Credit: Jacob W. Frank, National Park Service. Public domain.)

Natural geysers are rare on Earth; there are fewer than 1,000 worldwide, and about half of them are in Yellowstone National Park. Geysers, whose eruptions range from small bubbling pools, to roaring jets of water and steam that can reach a few hundred meters high, fascinate all who have the good fortune of witnessing one.

In a newly published paper, U. S. Geological Survey hydrologist, Shaul Hurwitz and his coauthor, geology professor Michael Manga at the University of California, Berkeley, synthesize the current state of knowledge about geysers. The authors review past research, and point the way to answering future questions. The “Annual Review of Earth and Planetary Sciences” is published once a year, and includes articles written by invitation only. The newly-published article about the science of geysers attempts to bring all the knowledge of geysers that has been gathered by scientists since the early 19th century together in one place and to improve our understanding of the influence of changing technology on scientific knowledge.

Because many of the processes associated with geyser eruptions are similar to those operating in volcanoes, understanding the mechanics of geysers and how they operate can lead to better understanding and predictions of volcanic eruptions. And because geyser eruptions are smaller and more frequent than volcanic eruptions, there is an opportunity to collect more data and develop approaches for integrating and interpreting geophysical and hydrological measurements to understand their geology, chemistry, underground “plumbing,” and the physical processes that control their behavior.

A better quantitative understanding of the processes that control geyser eruptions is also critical for their preservation, and can guide the protection and preservation of the unique and diverse geysers on Earth.

Almost a century and a half after the survey led by Ferdinand V. Hayden (his survey was a predecessor to USGS) 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.”

idealized line drawing showing a cross-section of a geyser, fumarole, and hot spring, and their underground workings.
Simplified diagram showing the underground structure of a typical geyser basin. Fumaroles form when boiling occurs below the ground surface, discharging water vapor (steam) or liquid water. The temperature of hot springs is either at or below the temperature of boiling water at the ground surface. In a geyser, liquid water and steam erupt episodically after water and steam bubbles accumulate in a side reservoir (“bubble trap”) where pressure builds prior to an eruption. These underground bubble traps are likely only a small part of much larger subsurface fracture and reservoir complexes. The source of the heat is usually an active or old dormant magmatic system and the source of water is precipitation recharged into the subsurface.(Public domain.)

Through monitoring eruption intervals, analyzing geophysical data, taking measurements within geyser conduits, performing numerical simulations, and constructing laboratory models, some of these questions have been addressed. Geysers are uncommon because they require a rare combination of abundant water recharge, magmatism (a source of heat), and large fractures and cavities in the rock. Geyser eruptions are driven by the conversion of thermal to kinetic energy during decompression. In other words, water deep in the ground is heated up by nearby hot rocks, and when conditions are just right, and the pressure of the overlying rocks is released, the water will erupt out of the ground as a geyser. Larger and deeper cavities within the rock permit larger eruptions and promote regularity by isolating water from weather variations at the Earth’s surface.

“Geysers are exceedingly complex hot springs, no two of which are alike,” said the late USGS geologist Donald White, who established the modern scientific definition for word, “geyser” in 1967. 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. Some of the earliest studies that led to the scientific understanding of geysers were done in Iceland by Robert Bunsen (of laboratory burner fame) in 1847.

Despite public interest and the long history of scientific study, there remain fundamental questions about geysers that continue to guide research efforts. Scientists are still addressing the fundamental processes behind geysers. Much of our knowledge about various aspects of geyser activity comes from visual observations made by park rangers and amateurs.

The new paper summarizes scientific progress in addressing fundamental questions about why some geysers erupt continuously while others erupt only intermittently. How old are some of the geyser edifices? Why aren’t all geysers the same? What natural processes govern the length, frequency, and behavior of geyser eruptions?

There is a long history of searching for external controls on geysers, and studies often draw contradictory conclusions even for the same geysers. Uncontroversial are the observations that regional and distant earthquakes can change geyser behavior, including the interval between eruptions, and that some geysers, such as several in Yellowstone, display seasonal cycles of eruption intervals.leslie

The full paper, “The Fascinating and Complex Dynamics of Geyser Eruptions,” was just published in the journal, Annual Review of Earth and Planetary Sciences.

 

RESOURCES:

From the U.S. Geological Survey:

Ages of Yellowstone geysers

Temperatures of Norris Geyser Basin, Yellowstone National Park

Accidental manmade “geyser” in Yellowstone in 1992

Old Faithful management report (the role of geyser science in maintaining park infrastructure)

Geyser postcard from the Yellowstone Volcano Observatory

From the National Park Service:

Yellowstone National Park

Live webcam on Old Faithful geyser in Yellowstone

Yellowstone hydrothermal features

Yellowstone geysers

Yellowstone geyser video

Predicting Old Faithful video