How Much Water Erupts From Old Faithful Geyser?

Editor's Note: 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 and Blaine McCleskey, research hydrologists with the U.S. Geological Survey.

Old Faithful Geyser was named by Ferdinand V. Hayden, who led the 1871 geological survey of northwestern Wyoming that resulted in the establishment of Yellowstone as the first U.S. National Park in 1872. In the report summarizing the expedition, Hayden wrote: “[Old Faithful] is so regular in its operations and they occur so frequently that it has afforded unusual facilities for observation”. There are many reasons to study geysers, and because of the relative regularity of its eruptions, Old Faithful has attracted a significant amount of attention for scientific research. Studies include temperature and pressure measurements and video observations in the conduit, analysis of seismicity associated with the eruption cycle and delineation of the subsurface structure, statistical analysis of eruption intervals and their modulation in response to large regional earthquakes, interaction with surrounding geysers, and response to seasonal and inter-annual precipitation patterns and severe and prolonged droughts. Studies have also documented deposits that are called “geyser eggs” and diverse microbes that thrive in pools on the geyser cone.

One of the most fundamental properties of any geyser is the volume of water erupted and the associated heat and the amount of chloride, arsenic, and fluoride (and other elements) in the erupted water. Measuring the volume of water at Old Faithful is challenging because the erupted water flows through several very shallow outflow channels, and wind can influence how much water actually ends up in these channels. Also, some of the water erupts as steam that mostly condenses in the air above the geyser, and some of the liquid water evaporates along the outflow channels before reaching points where it can be measured. Previous estimates of erupted volumes varied significantly, and the few past studies did not describe the methods used nor the number of eruptions captured. For example, there is no documentation of how the current estimate of erupted water volume provided by the National Park Service (14 to 32 cubic meters, or 3,700 to 8,400 gallons) was obtained. In short, there were no good estimates of the volumes for Old Faithful eruptions!

In a recent paper published in the Journal of Volcanology and Geothermal Research, scientists from the USGS, University of California, Davis, University of California, Berkeley, and the National Park Service quantified the total volume of water erupted during 45 Old Faithful Geyser eruptions, as well as the associated heat and mass. Under a research permit (YELL-SCI- 08342) with very specific guidelines for the work, a portable flume was placed in one of the geyser’s outflow channels and specific conductance was continuously measured in the adjacent Firehole River, into which the geyser’s water flows (specific conductance can provide a measure of how much water enters the river from a geyser or thermal basin). The measurements were supplemented by calculations to estimate the volume of water erupted as steam and to quantify the geyser's heat output. The calculated average volume of water discharged by Old Faithful Geyser eruptions was 27.9 cubic meters (7,370 gallons) but varied from 12.2 to 44.3 cubic meters (3,223 to 11,703 gallons). Unsurprisingly, the scientists found that short eruptions (less than 2.5-minute duration) erupted less water than the longer eruptions (typically 3–5 minutes). No relation between the volume of water erupted and the length of the preceding eruption interval was found.

This means that an average Old Faithful eruption is equivalent to 4 to 5 concrete mixer trucks or about 140 standard household bathtubs! It would take about 90 average Old Faithful eruptions to fill an Olympic-size swimming pool, which typically holds approximately 2,500 cubic meters (660,000 gallons).

How do the volumes of water that erupt Old Faithful compare with other geysers in Yellowstone? At Lone Star Geyser, about 5 km to the south-southwest of Old Faithful, the volume of erupted water varies between 15.4 and 28.1 cubic meters (4,068 to 7,423 gallons), with an average of about 21 cubic meters (5,548 gallons). At Steamboat Geyser in Norris Geyser Basin—the geyser with the tallest eruptive plume in the world—the volume of water erupted is significantly larger. Between 2018 and 2020, measured water volumes from individual eruptions ranged between 134 and 538 cubic meters (35,400 to 142,125 gallons).

Measuring the volumes of water erupted from Old Faithful is important because it can serve as a baseline to better enable detection of changes resulting from earthquakes, climate variability, changes in subsurface heat, and infrastructure development. This in turn can inform the management of tourism around one of the most iconic natural wonders in the US National Park system.