#cool rocks

If you can name one geyser in the world, chances are it's Old Faithful, and for good reason!

While it is not the tallest or most active geyser - and not necessarily even the most predictable - Old Faithful is a powerful combination of size, spectacle, regularity, and most important: accessibility. It is located in the Upper Geyser Basin of Yellowstone National Park, sited at the crown of a sinter hilltop mere steps from the Old Faithful Visitor's Center.

It was named during the famed Washburn Expedition of 1870, which led to the creation of Yellowstone as the first National Park in 1872. For as consistent as it has been for 150+ years, no mention of it exists before 1864.

It erupts in a gorgeous plume that reaches 90-180 feet into the sky, and according to new research, each eruption discharges an average of 7,300 gallons of water.

Old Faithful is a cone-type geyser, meaning the eruption jets from a small surface vent. Its remarkable consistency is in part due to a plumbing system that is relatively solitary and unconnected to other geysers, despite being located in one of the largest geyser fields on earth.

Much of what we know about how geysers work is because of Old Faithful. While scientific studies have been conducted on geyser plumbing systems, no one actually knows what they look like. In 1992/93, probes were lowered into OF's vent after an eruption, including a camera that, after descending through a narrow opening of only 4.5" (!!!! 7,300 gallons gets shoved up through a 4.5" tube!!!! what!!!! geysers are SO COOL) revealed an "automobile-sized" chamber about 35 feet down. Vibration and seismic equipment revealed what appears to be a a second massive chamber about 50 feet down. In 2016, additional seismic studies shed more light on its deeper plumbing system down to about 260 feet:

While its intervals have shifted slightly over the years, Old Faithful remains predictable with about 90% accuracy. What many people don't realize though, is that predicting the next eruption isn't as simple as starting a countdown when the eruption ends.

Old Faithful is a bimodal geyser that experiences two different types of eruptions: short and long, and the eruption mode influences the next prediction. "Short" eruptions have a duration less than 3.5 minutes, while "long" eruptions are over 3.5 minutes. Short eruptions generally result in a shorter interval between eruptions - approximately 60 minutes - while long eruptions result in a duration of closer to 90 minutes, with a window of approximately +/- 15 minutes. Every time OF erupts, park rangers and citizen scientists who utilize the Geyser Times app/website to log geyser activities, estimate the next eruption window based on the eruption type. Those estimations are also adjusted as needed when eruption patterns suggest any shifts in behavior.

There is no hiking required to see Old Faithful, which is part of what feeds its enduring fame. A paved ADA path makes it wheelchair friendly, and seating is available in the viewing area. Depending on the time of year and time of day you may need to bring some patience for the crowds, but Old Faithful is available to everyone, and it always puts on a show.

Are crowds a deal breaker? The crowds are gone by dinner time, and let me tell you, an Old Faithful sunset is pretty neat.

During certain times of year, Old Faithful also provides a unique night sky experience, with eruptions taking place under the Milky Way.

Old Faithful is one of over 150 geysers located in Upper Geyser Basin - the largest concentration of geysers in the world. Never been to Yellowstone? Never seen a geyser but would like to? Good news!

A volunteer-operated webcam on the roof of the Old Faithful Inn provides a 24/7 live stream of Upper Geyser Basin, with full or partial views of 5 regularly predicted major geysers, including Old Faithful, along with many other magnificent performers like Beehive, Giant, Grotto, and Lion. (I have this stream running in the background almost all the time - it's wonderful.) Occasionally, you'll see some furry guests in the form of bears, bison, coyotes, etc.