Old Faithful
Old Faithful is not a natural clock: its next eruption is predicted from the duration of the last, making observation more interesting than simply arriving for a show.
Artwork inspired by Conrad Schwiering
Old Faithful is one of nearly 500 Yellowstone geysers and one of only a handful that rangers regularly predict. Its median interval is about 102 minutes with a roughly 12-minute prediction window, though observed intervals can range from 54 to 118 minutes. Eruptions last roughly 1½ to 5 minutes, reach 106 to more than 180 feet, and release about 3,700 to 8,400 gallons of 203°F water.
The prediction is a measurement, not folklore. A short eruption expels less heat and water and generally recharges sooner; a long eruption requires a longer refill. Earthquakes and gradual plumbing changes have lengthened average intervals over time, including shifts after the 1959 Hebgen Lake and 1983 Borah Peak earthquakes. Watch the duration, note when the vertical water gives way to mostly steam, then compare the newly posted window with what you observed.
Do not spend the entire wait guarding a bench. The Upper Geyser Basin holds the world’s densest concentration of geysers, with accessible boardwalks leading toward Castle, Grand, Daisy, Riverside, hot springs, and runoff channels. Check the prediction at the visitor center, lodges, or NPS app; choose a short loop that fits the window; return before its early edge; and let wind direction determine which viewing side keeps the water column visible instead of hidden in steam.
- Typical interval
- 102 minutes, with a ±12-minute prediction window
- Eruption
- 1½–5 minutes; 106–180+ feet
- Water
- About 3,700–8,400 gallons per eruption
Quick guide
- Anchor
- The transition from a coherent water column to a steam-dominated plume near the eruption’s end
- Second focus
- Wind bending the plume while runoff begins moving across the pale sinter mound ↔ Bison-warmed ground, orange microbial channels, historic Old Faithful Inn, and other predicted geysers sharing the basin
How to read Old Faithful on site
- Read the window
- Use the visitor center, lodge displays, or NPS app after each eruption; an old screenshot is no longer a prediction.
- Watch the duration
- Time the water phase, because a short or long eruption helps explain why the next interval changes.
- Spend the interval
- Choose only the boardwalk loop that comfortably fits the posted window, then return before its earliest edge.
- Choose your side
- Use wind direction and sun angle: a cross-lit plume reads better than steam blowing directly toward the viewing area.
Good to know
Prediction staffing pauses when the visitor center closes, typically November 1–December 14 and March 16–April 16; the last posted time can remain visible without being current. In winter the area is reached by authorized oversnow transport, not an ordinary rental car. Bison regularly use warm basin ground and may interrupt a boardwalk route—wait for space rather than stepping off the path. Coins and thrown objects damage hydrothermal plumbing and cannot be safely retrieved.
Notice these
- The transition from a coherent water column to a steam-dominated plume near the eruption’s end
- Wind bending the plume while runoff begins moving across the pale sinter mound
- Bison-warmed ground, orange microbial channels, historic Old Faithful Inn, and other predicted geysers sharing the basin