Old Faithful

While not the largest in the park, the Old Faithful geyser is undoubtedly Yellowstone National Park’s most beloved and popular geyser. It is set apart from other geysers as being one whose recurring eruptions can be depended on to take place at a certain time. Its name reflects the regularity at which it erupts, with most of them being somewhat accurately predicted. Normally it faithfully erupts every 89 minutes plus or minus 10 minutes. Old faithful varies in height with measurements from 32.3 to 55 meters with an average of 39.6 meters. The eruptions generally last between 1.5 and 5 minutes expelling 14 to 31.7 cubic meters of water. The water is 95.6 degrees Celsius when it exits the vent. This is over the boiling point at Old Faithful’s elevation.

The geyser was ‘formally’ discovered in 1870 by the Washburn expedition. Back then the geyser erupted every hour or so. Since then the average interval between the eruptions has increased due to ongoing processes with its plumbing. The main factors affecting the plumbing are the earthquakes that happen in that region. Old Faithful’s interval was lengthened noticeably during the 1959 Hebgen Lake Earthquake, the 1983 Borah Peak Earthquake, and an earthquake near the geyser basin in 1998.

Every thermal feature has some kind of underground plumbing created by hot water mineral deposits. Old faithful is a silica based thermal feature. The silica is tough and difficult to break which allows for somewhat of a stable plumbing system despite the amount of pressure geysers create. Geysers are just hot springs with constrictions in their plumbing, often near the surface, that prevent water from just seeping out. This causes the pressure to build up and allows the water to be released in a spectacular show of force. As the water underground builds up pressure and heat, the surface boiling point (93 degrees Celsius) is often exceeded. The pressure with the weight of the water overlying on top prevents the water from boiling. The confined bubbles from boiling eventually lift the water up and cause a release of steam, water, and pressure. The water is expelled out of the main cone faster than it can enter the plumbing system around that cone. This allows the reservoir to empty completely before starting to fill up again.

There have also been relationships noted between the length of Old Faithful’s eruption and the length of the following interval. During a short eruption, less water and heat are discharged which causes a shorter recharge time. Longer eruptions mean that more of Old Faithful’s reservoir was used which means it will take a longer time to fill.

There are many myths and misconceptions about Old Faithful. Rangers in Yellowstone have been asked questions such as “Do you turn off Old Faithful for the night?” and “I will be in the park a month from now, what times will Old Faithful go off on October 27th?” Old Faithful is a natural wonder with no human involvement. The eruptions are predicted, but not to the exact minute.

If you wish to see Old faithful but aren’t planning to come to Yellowstone anytime soon, the park has a LIVE webcam that shows the Old Faithful eruption in real time. Today (9/27/12), the next predicted eruption is 1:45pm American Mountain Time. Link Below!


Old Faithful LIVE Camera: http://www.nps.gov/yell/photosmultimedia/yellowstonelive.htm
Photo Credit: Old Faithful Geyser at Sunset, Yellowstone National Park, 1920's NPS Historical Photograph
More info on Old Faithful: http://mms.nps.gov/yell/ofvec/exhibits/eruption/prediction/predict7.htm