Old Faithful

Old Faithful was named on September 18, 1870, by Henry D. Washburn during the Washburn-Langford-Doane Expedition, and it is generally described as the first geyser in the park to receive a name. Expedition member Nathaniel Langford later wrote that it spouted at regular intervals nine times during the party's stay, with columns of water roughly 90 to 125 feet high. In the park's early years visitors treated the crater as a natural laundry.

Each eruption sends roughly 3,700 to 8,400 US gallons (about 14,000 to 32,000 litres) of boiling water skyward. Heights range from about 106 feet to more than 180 feet, with a typical eruption reaching around 130 feet according to the National Park Service, and an eruption usually lasts between about one and a half and five minutes. Researchers who lowered probes into the conduit between 1983 and 1994 recorded water at 244 degrees Fahrenheit (118 degrees Celsius) at a depth of 72 feet, and later video probes saw superheated steam entering the channel.

Part of what makes Old Faithful dependable is that it is not thought to be plumbed into neighbouring features in the basin, so its behaviour is less affected by what other geysers are doing. Even so, the timing is not fixed. The NPS notes that the average interval has lengthened over the decades, partly because of earthquakes: before the 1959 Hebgen Lake earthquake the average was a little over an hour, and a 1983 Idaho quake also lengthened waits. As of January 2025 the NPS reported a median interval of about 102 minutes, give or take 10, with individual intervals ranging from roughly 54 to 118 minutes. Wikipedia gives a somewhat shorter long-term average of about 92 minutes, so treat any single figure as approximate. Rangers predict eruptions for Old Faithful and five other geysers, and the NPS posts those predictions at its visitor facilities and in its app.

Old Faithful sits in a basin the NPS says holds at least 150 geysers in about one square mile, along with many hot springs. Yellowstone as a whole has nearly 500 geysers, which the NPS says is close to 60 percent of all the geysers in the world. Boardwalks loop through the basin, so a visit can easily stretch beyond the main geyser to the other features in the basin, and the NPS posts predictions for several of them.

Beside the viewing area stands the Old Faithful Inn, built in 1903-1904 and described by the NPS as nearly 700 feet long and seven stories high. It is a National Historic Landmark and one of the few remaining log hotels in the country. Even visitors who are not staying there often step inside to see the lobby and its timber framing.

• Because intervals vary, the sensible approach is to check the posted prediction and arrive a little ahead of it rather than hoping to catch a random eruption.
• Stay on the boardwalks and follow NPS guidance throughout the basin; the ground around thermal features can be thin and the water is scalding.
• Check the NPS for current hours of visitor facilities, road access and conditions.
• On a Voyzo private tour, a private vehicle and driver collects you door to door and handles the drive and parking, which leaves your group free to time the eruption and wander the basin at its own pace.