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Geysers of the World   

Geysers of Yellowstone   



  Old Faithful
Feature Type: Geyser
Geyser/Spring Type: Cone geyser

Upper Geyser Basin
Old Faithfull Group

Old Faithful is a cone-type geyser. Since 2000 its intervals have varied from 44 to 125 minutes, with an average of about 90-92 minutes, its duration is 1 1/2 to 5 minutes and its height is 90 to 184 feet. The rangers say that 90% of their predictions are within +/- 10 minutes.
Old Faithful was named by the Washburn expedition of 1870. They were impressed by its size and frequency. It is not the biggest or most regular geyser in Yellowstone but it is the biggest regular geyser. Furthermore, it has been erupting in nearly the same fashion throughout the recorded history of Yellowstone. Through the years, it has become one of the most studied geysers in the park. One result of this close observation is that the Park Rangers are able to predict its eruptions fairly accurately. This makes Old Faithful geyser one of the easiest geysers in Yellowstone to see.

Old Faithful is deceiving. The benches around the geyser are over 300 feet from the geyser but with nothing to judge the distance by, I rarely realize just how big the geyser is until I get further away. Personally, I like the view from Geyser Hill. As with any geyser, watch the wind direction or you may only see steam.

Predicting Old Faithful:

It is not possible to predict more than one eruption in advance. Old Faithful is currently bimodal. It has two eruption durations, either a long (over 4 minutes) or more rarely a short (about 2-1/2 minutes). Short eruptions lead to an interval of just over an hour and long eruptions lead to an interval of about 1-1/2 hours.
In the past the interval was predicted using more precise measurements of the duration of the current eruption. The duration was timed from the first heavy surge which lifts water skyward at the start of the eruption until the last small splash above the cone at the very end. The longer the eruption lasted, the longer the interval until the next eruption. The following regression table was used.

Duration Interval
1.5min 51 min
2.0min 58 min
2.5min 65 min
3.0min 71 min
3.5min 76 min
4.0min 82 min
4.5min 89 min
5.0min 95 min
The above table is shown for historic purposes. Predictions are currently based only on short or long durations. This simpler prediction model still results in a 90 percent accuracy of the predictions.

Common Misconceptions:

Old Faithful plays on the hour every hour
This legend dates back to the early history of Yellowstone Park. Old Faithful has never played every hour on the hour. It is just as likely to play on the hour as it to play 17 minutes after the hour or 23 minutes after the hour or ......
Old Faithful plays hourly
Old Faithful's intervals vary from 35 minutes to 2 hours. You might see one interval of 60 minutes but it is very unlikely that you will see two in a row. This misconception seem to date back to the 1870 Washburn expedition where one of the members reported that Old Faithful played "nearly hourly". No geyser, including Old Faithful, plays at set times and intervals. There is always some variation.
Old Faithful is slowing down and becoming less regular
Part of this statement is true; part is not. Because of changes in circulation that resulted from the 1959 Hebgen Lake and 1983 Borah Peak earthquakes, as well as other local and smaller earthquakes, the average interval between eruptions has been lengthening during the last several decades. Old Faithful has slowed from an average of about 65 minutes from 1870 through 1947 to an average of 90-92 minutes from 2001 through 2010.
The range of intervals has also increased slightly, from about 60 minutes through the 1960s to about 80 minutes in more recent decades. However, regularity, as measured by the difference between actual intervals and average intervals or standard deviation, decreased during the most recent decade.
Old Faithful is getting shorter
Measurements show that Old Faithful is still as tall as it has ever been, 90-180 feet. There are a number of reasons people may feel that Old Faithful is getting shorter. They may have seen an exceptionally tall eruption last time and this time saw a more ordinary or even a short eruption. The first time they saw an eruption they may have been more excited and their excitement caused them to over estimate its height. Or they may have first seen it a number of years ago when it was possible to get closer to the geyser. To accommodate the summer crowds, the boardwalk has since been moved further back from Old Faithful. Many people don't realize just how far from the geyser the boardwalk is. With nothing to judge the distance by, most people severely underestimate the height of Old Faithful. Its not until they get back farther from the geyser and see the buildings around the geyser that they realize just how big the geyser is.
Old Faithful erupted late or early
It is only possible to make predictions of the time Old Faithful may erupt. The geyser will erupt when it is ready. Its the prediction that is early or late not the geyser.

What to look for:
A crowd gathered around any geyser is often an indicator of an imminent eruption. After an eruption of Old Faithful everyone that was seated around the benches leaves. Especially in summer as the predicted time for the next eruption approaches, the benches begin to fill and eventually overflow. Thus, by looking at the crowd, you can get a rough idea as to when the next eruption is predicted.

If crowds are sparse or non-existent you'll have to look at the geyser itself. 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 less than a minute, the eruption starts waning. The interval to the next eruption is based on the total duration of the current eruption. This includes the unimpressive play that ends the eruption. The main visible difference between a long and short eruption is the duration of the end play. In a short duration eruption the end play stops quickly. In a long duration eruption you may see up to 4 minutes of unimpressive, 5 feet tall, end play.

Electronic Monitor Files
Old Faithful eruptions for 2000.TXTOld Faithful eruptions for 2001.TXT
Old Faithful eruptions for 2002.TXTOld Faithful eruptions for 2003.TXT
Old Faithful eruptions for 2004.TXTOld Faithful eruptions for 2005.TXT
Old Faithful eruptions for 2006.TXTOld Faithful eruptions for 2007.TXT
Old Faithful eruptions for 2008.TXTOld Faithful eruptions for 2009.TXT
Old Faithful eruptions for 2010.TXTOld Faithful eruptions for 2011.TXT

Some of the temperature data used to derive the eruption times and durations used in this section were collected by Ralph Taylor under a National Park Service research permit, and the remainder was collected by personnel working for the Geology Department of the Yellowstone Center for Resources (including Ralph Taylor). The loggers are a combination of loggers owned by the NPS and Ralph Taylor. Analysis of the raw temperature data to extract the eruption data was performed by Ralph Taylor. The eruption time files on this website may be used provided that Yellowstone National Park is credited for the temperature data and Ralph Taylor is credited for the eruption times.

Activity Recorded by Data Logger - by Ralph Taylor  

Old Faithful Geyser has been monitored electronically using data loggers at least since 2000 (the first year for which I have found data files). There was an infrared system that recorded temperatures on a paper chart before that, but the data is not available in electronic form. The data logger for Old Faithful measures the runoff water temperature at a point about 20 meters (a rough estimate at best) from the vent toward the west. The sensor picks up preplay and the eruption start, with a delay of between one and ten minutes from the visual times recorded in the OFVC logbook. The mean delay for a period of several months in 2001 was found to be 3m46s with a standard deviation of 1m05s. The position of the sensor is far enough from the geyser that the eruption duration cannot be determined from the temperature trace.

It has been known for many years that Old Faithful's eruptions can be predicted by timing the duration an eruption and using a regression formula to find the expected interval to the next eruption. Since the data logger information does not contain duration information, it is not possible to find the regression data from the data set or to classify eruptions by duration.

In recent years Old Faithful has had increasing numbers of "long" eruptions (more than about 3m30s duration) and very few "short" eruptions. There are few eruptions of intermediate duration. Since this behavior pattern became established, predictions have been made using one prediction interval for short duration eruptions and another for long duration eruptions (with some special handling of the few intermediate duration eruptions).

For the purpose of the analysis presented here, I have only interval data, so I have classified eruptions as long or short based only on the interval.

Activity in 2011  
The overall statistics for 2011 are shown at Old Faithful 2011 Statistics. This summary gives the statistics for all intervals, and separately for long and short intervals for the current year-to-date, the past month, and the past week. A pdf of this summary is at Old Faithful Recent Activity Summary.

The interval graph shows all of the intervals for 2010. The orange triangles mark instances of short intervals. The graph is updated about every six weeks.
Click for a larger image

The next graph shows the intervals for the three months preceding the last data download at an expanded time scale. Again, the orange triangles denote short intervals, which often occur in clusters separated by days of exclusively long intervals.

In recent months Old Faithful is showing signs of returning to an old pattern of alternating long and short eruptions (and therefore intervals).

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This graph shows the activity for the month preceding the last download. The graphs all include a blue line showing all intervals, a green or yellow line showing the moving median interval. The orange triangles at the 43 minute levels denote the short intervals. In the past few years short intervals have tended to occur in clusters separated by periods of days or even a week with no intervals less than 1h15m. In the years that I have been analyzing Old Faithful, there have been no recorded instances of successive short intervals.
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The interval distribution shows that the greatest number of intervals were between 1h30m and 1h35m, which contains about a third of the long intervals. The category between 1h0m and 1h05m contains most of the short intervals.

Note that in the histograms displayed here the labels shown on the X-axis represent the upper boundary of the class, not the midpoint. Geyser times are traditionally truncated. The graph at the right has class widths of 5 minutes. The bar appearing above the label "01:35," for example, contains intervals from 1h30m through 1h34m (90 to 94 minutes).

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The second histogram, which shows the distribution of intervals with a resolution of one minute six seconds shows the main cluster of intervals around the 90 minute mark.
Again, recall that the label represents the high limit of the class, for example, the label "1:33" is the upper boundary of a class that contains intervals ranging from 1h32m1s to 1h32m59s, the class labeled "1:33"
contains intervals of 1h32m (92 minutes).

I shifted this histogram to 1m6s to match the logging interval I adopted in 2010 to allow for full-winter runs of the data logger.

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The final chart in this section is a representation of where the actual intervals occur in the prediction window. The chart includes results for the past week and month.
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Activity since 2000  
Old Faithful has been consistent in its behavior for the years covered by the data logger information. A simple plot of interval vs time (shown at right) does not reveal any noticeable change. There are two large gaps in coverage, one in early 2002 and one in early 2005, both caused by equipment problems. A few shorter gaps resulted when downloads were delayed due to winter conditions and the logger memory filled.
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More detail about the long-term variation in a geyser's behavior is often shown by a moving median graph, which eliminates the very long and very short intervals and gives a good picture of the overall behavior. For Old Faithful since 2000 this plot (at right), shows a slow increase in intervals throughout 2001, amounting to four minutes increase in that year. Since that time, the median interval has remained fairly steady with some fluctuation.
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Another way to look at the long term behavior is to plot a graph of the interval distribution for the different years. The graph at the right shows this plot. The shape of the distribution has remained generally the same since 2000, confirming the lack of change in Old Faithful in that time. The curve for 2009 shows a slight shift to shorter intervals.
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Finally, the chart at right shows how the maximum, minimum, mean, and median intervals for each month have changed. Since April of 2002 there was essentially no change in Old Faithful's behavior until 2007 when the mean interval decreased slightly. Note also that there is no visible seasonal change in Old Faithful's intervals.

Although past earthquakes (notably the 1959 Hebgen Lake quake and the 1983 Mt. Borah, ID quakes) were followed by noticeable increases in Old Faithful's intervals, the Denali AK quake in November of 2002 did not result in a measurable change in Old Faithful, even though it did result in changes in several other Yellowstone geysers, such as Daisy, Castle, and Lone Pine geysers.

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Activity in 2010
Activity in 2009
Activity in 2008
Activity in 2007
Activity in 2006
Activity in 2005

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A vintage picture of Old Faithful's crater by Haynes. Park visitors are no longer allowed so close to this geyser.

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Old Faithful Geyser as seen with the crowd from the benches around the geyser.

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This is a picture of Old Faithful Geyser as seen from Geyser Hill.

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Please note - this site is currently under constuction. Please visit for more information.  Last update 01-29-2017

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