Steamy Bubbles May Control Old Faithful’s Clock – GWC Mag

Every 60 to 90 minutes, a crowd of tourists accumulates to see the world’s most famous geyser spout in Yellowstone National Park, in Wyoming. We know why this happens: A periodic process causes the underground pool of superheated water to flash boil, pushing thousands of liters of water up through the spout. But what happens in the run-up to this regular spark is still steeped in mystery.

Now, scientists have built a miniature Old Faithful in the lab to resolve one of the geyser’s lingering questions: What causes the seemingly erratic dips and jumps in underground water levels between eruptions? Their explanation might help us understand both geysers and their deadlier cousins, volcanoes.

“The water inside Old Faithful is sloshing up and down quite vigorously between eruptions.”

“The water inside Old Faithful is sloshing up and down quite vigorously between eruptions,” said geophysicist Maxwell Rudolph of the University of California, Davis, who spearheaded the research. The column of liquid in the vertical shaft under the geyser’s outlet jumps and falls by a meter every second. Rudolph and his team believe they know why and described their theory in a poster at AGU’s Annual Meeting 2023 in San Francisco.

Hidden Boiling Chambers

The researchers turned to a hypothesis first published in 1811: the “bubble trap.” Hydrologists know that an underground reservoir of boiling water powers Old Faithful. The bubble trap idea posits that this cavern is off to the side of the main vent and connected to it via a horizontal tunnel, not directly underneath the spout. This offset causes the giant fluctuations in liquid, scientists believe.

Unlike steam from water boiling in a pot, the bubbles in this subterranean cauldron have nowhere to escape to. Instead, steam gets “trapped” at the chamber’s ceiling until enough pressure builds to push the water down below the level of the horizontal tunnel. Then, once every second, a bubble of steam bursts out sideways and into the vertical shaft, forcing its water level up and down. The bubble trap refills with water and the process starts over.

To put this idea to the test, the scientists built a miniature version of Old Faithful in their lab, consisting of a big tank of water (the trap) with a horizontal tube connecting it to a vertical spout. When they heated the tank to boil the water, they saw the bubbles repeatedly build up and escape, causing the liquid in the vertical tube to surge up and down, just as expected.

They compared their homemade geyser to the real Old Faithful using prior footage from cameras lowered into the geyser’s shaft. Using a simple mathematical model, they showed that the bubble trap hypothesis explained the observed physics, both in their lab creation and at Yellowstone.

Old Faithful’s Rougher Relatives

“It’s a natural laboratory for studying more hazardous systems.”

“It’s exciting that they’re able to measure these high-frequency oscillations in the system, which we also see at magmatic volcanoes,” said Earth scientist Leif Karlstrom of the University of Oregon, who was not involved in the research. “You can’t stick a pressure sensor down into a volcano, but you can do that in a geyser. It’s a natural laboratory for studying more hazardous systems.”

Rudolph and his colleagues are continuing to explore the connections between eruptions at geysers and volcanoes. “Explosive volcanic eruptions like Mount St. Helens are propelled by the expansion of gas, which is the same thing as in geysers,” said Rudolph.

Researchers have successfully applied geyser science to volcanoes before. After seeing horizontally offset reservoirs below geysers, scientists sought and found volcanoes with similarly offset magma chambers. Previously, lava pools were thought to sit directly below volcanoes’ spouts.

Geyser eruptions offer one further advantage to scientists: frequency. “Natural geysers erupt with intervals between eruptions of minutes to hours, so you can do a field experiment for a week and measure thousands of eruption cycles,” said Rudolph. “But a given volcanic center might erupt once within a human lifetime, or not at all.”

—Joseph Howlett, Science Writer

Citation: Howlett, J. (2023), Steamy bubbles may control Old Faithful’s clock, Eos, 104, https://doi.org/10.1029/2023EO230491. Published on 19 December 2023.

Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Related