How Much Water Does Old Faithful Really Erupt?
If you’ve ever stood among the crowds in Yellowstone National Park waiting for Old Faithful Geyser to erupt, you’ve probably wondered: just how much water is actually shooting into the air?
Well, we finally have a more precise answer thanks to a dedicated team of researchers from the USGS, University of California, Davis, University of California, Berkeley, and the National Park Service.
For decades, estimates of Old Faithful’s output were surprisingly rough. Scientists knew it erupted thousands of gallons of water, but exactly how much? That remained unclear due to the many ways in which water from an erupting geyser is carried away.
Old Faithful doesn’t just pour water neatly into a bucket. Instead:
- Some water erupts as steam and condenses in the air
- Some evaporates before it can be measured
- Wind can blow water away from measurement channels
- Water spreads through multiple shallow runoff paths
A recent study by the U.S. Geological Survey and partners changed that. By carefully measuring 45 separate eruptions using new techniques—read more about these techniques in the research paper here—researchers finally pinned down a reliable number.
On average, Old Faithful ejects about 7,370 gallons of water per eruption, but eruptions range between about 3,200 gallons and up to 11,700 gallons. The study found that longer eruptions tend to release more water, while shorter ones produce less. But interestingly, how long you wait between eruptions doesn’t seem to affect how much water comes out next.
So even if Old Faithful takes a little longer to erupt, it doesn’t necessarily mean a bigger show.
What Does That Much Water Look Like?
Numbers are helpful, but let’s put this into perspective.
An average eruption from Old Faithful is roughly equal to:
- 140 household bathtubs
- 4–5 concrete mixer trucks full of water
And if you’re thinking big:
Not bad for something that goes off about every 90 minutes.
Photo: Brian Doyle
How Does Old Faithful Compare?
Old Faithful is famous, but it’s not the biggest geyser in Yellowstone.
For example:
- Nearby Lone Star Geyser produces slightly less water on average
- Steamboat Geyser—the world’s tallest active geyser—can erupt 35,400 to 142,125 gallons in a single event
Old Faithful’s claim to fame isn’t size, it’s consistency!
Why This Research Matters
Understanding how much water Old Faithful erupts isn’t just trivia. These measurements help researchers:
- Track how geysers respond to earthquakes and climate changes
- Monitor shifts in underground heat systems
- Better manage tourism in one of America’s most visited natural areas
In other words, knowing how much water erupts today helps scientists detect when something changes tomorrow.
