Yes, Old Faithful is still faithful. As of January 2025, the geyser erupts with a median interval of 102 minutes, give or take about 10 minutes. That’s predictable enough for the National Park Service to post estimated eruption times so visitors can plan their day around it. But “faithful” doesn’t mean “unchanged.” The geyser has slowed considerably over the decades, and its long-term future depends on factors that aren’t guaranteed.
How Predictable It Actually Is
Old Faithful earned its name in 1870 not because it was the biggest or most spectacular geyser in Yellowstone, but because it went off on a schedule visitors could count on. That reliability continues today. Each eruption lasts between 1.5 and 5 minutes, shoots boiling water 106 to 184 feet into the air, and expels roughly 3,700 to 8,400 gallons per burst. The geyser erupts about 14 to 17 times every 24 hours.
The Park Service predicts each eruption based on a simple relationship: the longer the previous eruption lasted, the longer the wait until the next one. A short eruption (around 2 minutes) typically means a shorter interval of roughly 68 minutes. A long eruption (4 to 5 minutes) pushes the next interval closer to 94 minutes or more. This pattern is consistent enough that rangers can give visitors a prediction window accurate to within about 10 minutes. You can check the next predicted eruption time on the NPS website or at the visitor center.
Intervals do range from as short as 54 minutes to as long as 118 minutes, so there’s real variability within that window. But compared to almost every other geyser on Earth, Old Faithful is remarkably consistent.
It’s Slowing Down
The geyser is faithful, but it’s not the same as it used to be. In the summer of 1959, the average interval between eruptions was just 61.8 minutes. Today that figure sits around 102 minutes. That’s a roughly 65% increase in wait time over about six decades.
Some of that shift may trace back to the magnitude 7.3 Hebgen Lake earthquake in 1959, which struck just west of Yellowstone. For the first few days after the quake, Old Faithful’s eruptions became more erratic, alternating between longer and shorter intervals. By the end of that year, the average interval had crept up to 67.4 minutes. But the USGS notes that this kind of alternating behavior had been observed before the earthquake too, so it’s unclear how much the quake itself was responsible versus a trend already underway. What’s clear is that the interval has continued to lengthen steadily ever since.
Why It Works at All
Most geysers are wildly unpredictable. Yellowstone’s Steamboat Geyser, the world’s tallest active geyser, can go days or years between eruptions with no reliable pattern. Old Faithful’s consistency comes down to its unusual plumbing.
USGS research has mapped the underground system feeding the geyser. The main conduit runs roughly vertical from about 65 to 260 feet deep, but it’s offset about 65 feet southwest of the surface vent. Near the top of this deeper conduit sits a bubble-trap structure: a natural chamber where superheated water and steam build up pressure until the system reaches a tipping point and erupts. After the eruption releases that pressure, groundwater refills the chamber at a relatively steady rate, restarting the cycle. The water feeding eruptions doesn’t come from directly beneath the geyser but flows in from the side, which may help explain why the recharge process is so consistent.
What Could Disrupt It
Old Faithful has shut down before. Researchers studying mineralized wood deposits around the geyser found that during a severe drought in the 1200s, the geyser stopped erupting entirely. Trees grew right in the geyser’s runoff channels, something impossible during normal activity. The drought was severe enough to drop groundwater levels below the threshold needed to feed eruptions.
This matters because the water fueling Old Faithful isn’t the rain and snow falling directly on the geyser basin. Precipitation recharges the regional groundwater, which builds the hydraulic pressure that pushes hot water to the surface. In years with less precipitation, eruption intervals tend to stretch longer. In wetter years, they shorten. The chemistry of the ejected water has stayed nearly constant for over 120 years, meaning the deep thermal system itself is stable. The variable is how much water is available to feed it.
Climate projections for the western United States forecast increasingly severe droughts through mid-century. If those projections hold, eruption intervals could continue to lengthen, and in an extreme scenario, eruptions could cease temporarily, as they did 800 years ago. That’s not an imminent threat, but it places Old Faithful’s “faithfulness” in a longer context: the geyser depends on a water supply that isn’t infinite.
How Old Faithful Compares to Other Geysers
Yellowstone contains roughly half the world’s active geysers, but only a handful are predictable enough for the Park Service to post forecasts. Old Faithful is the most famous, but Daisy, Grand, and Castle geysers also receive predictions when conditions allow. Of these, Old Faithful has the tightest prediction window and the most consistent behavior. Grand Geyser, for instance, erupts roughly every 6 to 7 hours but with enough variability that visitors sometimes wait much longer than expected.
Old Faithful’s real distinction isn’t size or power. It’s that you can show up, check the prediction board, and be reasonably confident you’ll see an eruption within about 20 minutes of the posted time. For a natural phenomenon powered by superheated water and underground pressure chambers, that level of reliability is genuinely rare. It’s slower than it once was, and it depends on conditions that could change, but for now, Old Faithful lives up to its name.