Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Sin-Mei Wu, Jamie Farrell, and Fan-Chi Lin, seismologists with the University of Utah Seismograph Stations and Department of Geology and Geophysics.

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With all eyes on the spectacular eruptions of Steamboat Geyser, it’s easy to lose sight of the fact that, around three hundred feet away, Cistern Spring gradually drains a few hours after the amazing water show at Steamboat. In the 24 hours after Steamboat water eruption, Cistern Spring empties, only to begin refilling once more and recovering its normal water level within a few days.  This pattern has persisted since the 1960s and continues in Steamboat’s current active phase, which began in March 2018. 

It is actually not uncommon for separate hydrothermal features to have some sort of relation in time.  A good example is Beehive Geyser, near Old Faithful in the Upper Geyser Basin—spectacular Beehive eruptions always occur a few minutes after activity at a smaller adjacent “indicator” vent. These types of connections are thought to be a reason for the regularity of some eruptions, as the hydrothermal features may compete with each other for water and heat resources in the subsurface. In most cases, however, features that seem to be linked, like Beehive Geyser and the Beehive indicator, are immediately adjacent to one another (often within 10 feet (about 3 meters)).  In contrast, Steamboat Geyser and Cistern Spring have a much larger separation—about 330 feet (approximately 100 meters)! This raises questions regarding the underground water plumbing. How are Steamboat and Cistern connected? And does the plumbing geometry affect the eruption dynamics and regularity of Steamboat Geyser? 

To look for answers to these questions, the University of Utah, in collaboration with Yellowstone National Park, installed seismic arrays around Steamboat Geyser and Cistern Spring  in both summer 2018 and 2019 (under Yellowstone research permit YELL-2019-SCI-8058 and YNP permit 2016-9). Similar to the approach that illuminated the underground plumbing of Old Faithful, the seismic arrays offer a non-intrusive way to pin down the seismic source that originates from bubble formation and collapse when the system is recharging, which can provide four-dimensional views of the underground hydrothermal plumbing system.

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The work, recently published in Journal of Geophysical Research, found that Steamboat and Cistern’s plumbing structures extend to at least 450 feet (about 140 meters) deep, which is much much greater than what was found previously at Old Faithful (~260 feet, or 80 meters)! Steamboat’s conduit is approximately vertical to 400 feet (120 meters) deep. Surprisingly, Cistern’s plumbing includes a shallow vertical conduit connecting to a deep, large, and laterally offset reservoir ~200 feet (60 meters) southeast of the spring. Even more interestingly, there’s no direct connection between Steamboat and Cistern that can be imaged in the upper ~400 feet (120 meters). This indicates both systems are probably connected through a network of cracks instead of via “open pipes”.

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From the recent multidisciplinary work at Steamboat and other geysers it has become clear that deeper storage of energy within the plumbing system may give rise to more powerful (and taller) eruptions. This might explain the origin of Steamboat’s impressive eruptions—it is the tallest geyser in the world, after all. However, there is still little understanding about the role of the large reservoir connected with Cistern and whether this structure influences eruptions from Steamboat Geyser. Understanding these relations will require a more detailed study of fluid and heat transfer within the fractured medium of the subsurface.

Campaign-style seismic deployments only allow scientists to record signals within a short window of time. These findings provide a baseline to better understand the system, but the question remains: what is the nature of seismic sources when Steamboat is in a less active phase?  And how might continuous monitoring be used to better understand the Steamboat-Cistern system?. Hopefully, future experiments will provide even more insights into Steamboat’s spectacular eruptions and its fascinating relation with Cistern Spring!