Old Faithful
Old Faithful Page
Old Faithful
Yellowstone’s Famous Geyser

Posted November 2021

Old Faithful on a US Map
Old Faithful is in Wyoming:
Yellowstone National Park is the entire north west corner of Wyoming

Old Faithful Geyser


iscovered in 1870 by the Washburn Expedition, Old Faithful geyser was named for its frequent and somewhat predictable eruptions, which number more than a million since Yellowstone became the world's first national park in 1872.

  • Old Faithful can vary in height from 100-180 feet with an average of 135 feet. This has been the historical range of its recorded height.
  • Eruptions are normally between 1 1/2 to 5 minutes long
  • It currently erupts around 20 times a day

These eruptions are predicted with a 90 percent confidence rate, within a 10 minute variation, based on the duration and height of the previous eruption

  • Intervals can range from 60-110 minutes

People speak of the average time between eruptions. This is misleading. The mathematical average between eruptions of Old Faithful is currently 74 minutes, but it doesn't like to act average!

  • Prior to the 1959 earthquake, Old Faithful erupted 21 times per day. That's a significant decrease in activity for geologists tracking each eruption.

How many gallons of water are expelled during an eruption?
It depends on the duration of the eruption. Scientists estimate that the amount ranges from 3,700 gallons for a short duration of 1.5 minutes to 8,400 gallons for a longer duration of 4.5 minutes.

  • The water temperature at the vent during an eruption has been measured at 204 degrees
  • The steam temperature has been measured above 350 degrees! The scalding mist can reach 90 to 120 feet into the air

Yellowstone brings in upwards of 4 million visitors a year


November 2021

Yellowstone National Park:

World's First National Park:
The park's wildlife and scenery might be as well-known today, but it was the unique thermal features like Old Faithful Geyser that inspired the establishment of Yellowstone as the world's first national park in 1872.

500 Geysers:
Old Faithful is one of nearly 500 geysers in Yellowstone and one of six that park rangers currently predict. It is uncommon to be able to predict geyser eruptions with regularity and Old Faithful has lived up to its name, only lengthening the time between eruptions by about 30 minutes in the last 30 years.

Lava flows:
Thermal features change constantly and it is possible Old Faithful may stop erupting someday. Geysers and other thermal features are evidence of ongoing volcanic activity beneath the surface and change is part of this natural system. The hills surrounding Old Faithful and the Upper Geyser Basin are reminders of Quaternary rhyolitic lava flows. These flows, occurring long after the catastrophic eruption of 600,000 years ago, flowed across the landscape like stiff mounds of bread dough due to their high silica content.

Area was buried under ice:
Evidence of glacial activity is common, and it is one of the keys that allows geysers to exist. Glacier till deposits underlie the geyser basins providing storage areas for the water used in eruptions. Many landforms, such as Porcupine Hills north of Fountain Flats, are comprised of glacial gravel and are reminders that as recently as 13,000 years ago, this area was buried under ice.

Erosion and mountain building:
Signs of the forces of erosion can be seen everywhere, from runoff channels carved across the sinter in the geyser basins to the drainage created by the Firehole River. Mountain building is evident as you drive south of Old Faithful, toward Craig Pass. Here the Rocky Mountains reach a height of 8,262 feet, dividing the country into two distinct watersheds.

Is Old Faithful as "faithful" as always
Since its formal discovery in 1870, Old Faithful has been one of the more predictable geysers. Over time, the average interval between eruptions has increased, in part due to ongoing processes within its plumbing. Changes also result from earthquakes. Prior to the Hebgen Lake Earthquake (1959), the interval between Old Faithful's eruptions averaged more than one hour. After the earthquake, it started erupting with two distinct intervals—a short and a long one. Its average interval increased. After the 1983 Borah Peak Earthquake, centered in Idaho, it increased again. In 1998, an earthquake near Old Faithful lengthened the interval again; subsequent earthquake swarms further increased intervals. Sometimes the average interval decreases.

What animals are in this area? Bison, elk, bears...
Hydrothermal basins provide important habitat for wildlife in the Old Faithful area. Bison and elk live here year-round. In the winter, they take advantage of the warm ground and thin snow cover. Both black and grizzly bears are seen, especially during the spring when winter-killed animals are available. In summer, yellow-bellied marmots are frequently seen in the rocks behind Grand Geyser and near Riverside Geyser. Thermophiles live in the runoff channels of hot springs and geysers, providing food for tiny black ephydrid flies. The flies, in turn, lay their eggs in salmon-colored clumps just above the water surface where they are then preyed upon by spiders. Killdeer also feast on the adult flies.

The Upper Geyser Basin:
Yellowstone, as a whole, possesses close to 60 percent of the world's geysers. The Upper Geyser Basin is home to the largest numbers of this fragile feature found in the park.

Within one square mile there are at least 150 of these hydrothermal wonders.

150 Geysers in one square mile:
Of this remarkable number, only five major geysers are predicted regularly by the naturalist staff.

  • Castle
  • Grand
  • Daisy
  • Riverside
  • Old Faithful

There are many frequent, smaller geysers to be seen and marveled at in this basin as well as numerous hot springs and one recently developed mudpot (if it lasts).


Water Vaporizing:
Under normal conditions, water heated to its boiling point vaporizes, but water in hot springs buried deep underground has no opportunity to vaporize. As a result, the water can actually exceed the temperature of its boiling point while remaining a liquid. Geysers result when such hot springs occur with small outlets near the surface. When the superheated water does rise, it begins vaporizing even before it reaches the surface. The bubbles' steam pushes the geyser's water above the ground in explosive eruptions.


Volcanic Rock heats ground water:
For at least the past 150 years, Old Faithful has reliably spewed bursts of steam and hot water every hour to hour and a half. More than 100,000 eruptions of the geyser have been recorded. Geysers are rare features on Earth; only about 1,000 of them exist and more than half of those are located in Yellowstone. For a geyser to form there must be a volcanic heat source, abundant ground water, and a geologic plumbing system (fractures, fissures and other open spaces in rock) through which the heated water can escape.

The water escapes when the ground water is heated to boiling by the hot volcanic rocks. Expanding steam bubbles push the water overhead through the fissures in the rock until they overflow from the geyser. The escape of the top layers of water decreases the pressure on the hotter waters below, causing a chain reaction of violent steam explosions that expand the volume of the rising, boiling water by 1,500 times or more. This superheated water then bursts into the sky to form a geyser's familiar fountain.


What makes a geyser?
Geysers are made from a tube-like hole in the Earth's surface that runs deep into the crust. The tube is filled with water. Near the bottom of the tube is molten rock called magma, which heats the water in the tube.

Water in the lower part of the tube, close to the magma, becomes superhot. Gradually, it begins to boil. Some of the water is forced upward. The boiling water begins to steam, or turn to gas. The steam jets toward the surface. Its powerful jet of steam ejects the column of water above it. The water rushes through the tube and into the air.

The eruption will continue until all the water is forced out of the tube, or until the temperature inside the geyser drops below boiling


Yellowstone Geyser Yellowstone Geyser

Old Faithful:
  • Named by the first official expedition to Yellowstone, the Washburn Expedition of 1870.
  • They were impressed by its size and frequency.
  • Old Faithful erupts every 35 to 120 minutes for 1 1/2 to 5 minutes.
  • Its maximum height ranges from 90 to 184 feet.
  • It is not the biggest or the most regular geyser in Yellowstone but it is the biggest regular geyser.
  • It has been erupting in nearly the same fashion throughout the recorded history of the park.

The Eruption:
Old Faithful goes through a period of preplay prior to an eruption. This preplay can last anywhere up to twenty minutes. The preplay consist of splashing and small jetting which often occurs every few minutes reaching from 1 to (rarely) 20 feet in height. It often lasts just long enough for some excited visitors to start taking pictures.

The eruption usually starts from what initially looks like just another preplay jet. Short interval eruptions occasionally start with the first splash seen above the cone but most require a period of preplay. Once the eruption starts, the jetting will grow, stop, grow again and in two or three of these steps, reach maximum height. It takes 10-20 seconds to reach full height. Unfortunately, the full height is maintained only for a short time. Within a minute, the eruption starts waning.

  • Through the years, it has become one of the most studied geysers. One result of this close observation is that the Park Rangers are able to predict its eruptions fairly accurately.

Old Faithful is not slowing down:
People expecting an hourly eruption are often surprised when they have to wait through a 90 minute to 2 hour interval. They then think that Old Faithful is slowing down. Old Faithful still has its same interval range, 35-120 minutes, that it has always had.

In the last few years, long interval eruptions have been a little more common than they were a few decades so the yearly average has increased by a few minutes over what it was a few decades ago but this change is very small and the range of intervals is still the same.

  • Old Faithful is deceiving. The benches around the geyser are over 300 feet from the geyser but with nothing to judge the distance by


Old Faithful is the most famous, though not the highest, of all North American geysers

  • Precisely when the next eruption will occur is determined by the duration of the preceding eruption: the longer an eruption, the longer the interval to the next eruption.

After the 1983 Borah Peak (Idaho) earthquake, those intervals became increasingly less predictable, although detailed measurements made since 2000 revealed that most eruptions fell generally within a range of approximately 60 to 110 minutes, the average being roughly every 90 minutes.

Old Faithful is an example of a cone geyser. Cone geysers are visible on Earth's surface as mounds of porous deposits of siliceous sinter (geyserite). Cone geysers typically produce steady eruptions lasting several seconds or minutes.


Old Faithful is a cone geyser in Yellowstone National Park in Wyoming, United States

  • It was named in 1870 during the Washburn - Langford - Doane Expedition and was the first geyser in the park to be named.

In the afternoon of September 18, 1870, the members of the Washburn - Langford - Doane Expedition traveled down the Firehole River from the Kepler Cascades and entered the Upper Geyser Basin. The first geyser that they saw was Old Faithful. Nathaniel P. Langford wrote in his 1871 Scribner's account of the expedition:

It spouted at regular intervals nine times during our stay, the columns of boiling water being thrown from ninety to one hundred and twenty-five feet at each discharge, which lasted from fifteen to twenty minutes. We gave it the name of "Old Faithful." - Nathaniel P. Langford, 1871

  • It is a highly predictable geothermal feature and has erupted every 44 minutes to two hours since 2000
  • In the early days of the park, Old Faithful was often used as a laundry

Old Faithful is sometimes degraded by being made a laundry. Garments placed in the crater during quiescence are ejected thoroughly washed when the eruption takes place. Gen. Sheridan's men, in 1882, found that linen and cotton fabrics were uninjured by the action of the water, but woolen clothes were torn to shreds.

  • More than 1,000,000 eruptions have been recorded
  • Harry Woodward first described a mathematical relationship between the duration and intervals of the eruptions in 1938
  • Old Faithful is not the tallest or largest geyser in the park; those titles belong to the less predictable Steamboat Geyser

The reliability of Old Faithful can be attributed to the fact that it is not connected to any other thermal features of the Upper Geyser Basin

  • Eruptions can shoot 3,700 to 8,400 gallons of boiling water to a height of 106 to 185 feet lasting from 1 1/2 to 5 minutes
  • Intervals between eruptions can range from 60 to 110 minutes, averaging 66.5 minutes in 1939, slowly increasing to an average of 90 minutes apart today, which may be the result of earthquakes affecting subterranean water levels
  • After the Borah Peak earthquake in central Idaho in October 1983, the eruption intervals of Old Faithful were noticeably lengthened

Within a margin of error of + or - 10 minutes, Old Faithful will erupt either 65 minutes after an eruption lasting less than 2 1/2 minutes, or 91 minutes after an eruption lasting more than 2 1/2 minutes.

  • Water inside is 244 degrees

Between 1983 and 1994, four probes containing temperature and pressure measurement devices and video equipment were lowered into Old Faithful. The probes were lowered as deep as 72 feet. Temperature measurements of the water at this depth were 244 degrees, the same as was measured in 1942.


Old Faithful Geyser Predictions:

Old Faithful is located in Yellowstone's Upper Geyser Basin in the southwest section of the park.

Old Faithful