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Geysers of the World   

Geysers of Yellowstone   



  Great Fountain Geyser
Feature Type: Geyser
Geyser/Spring Type: Fountain geyser

Lower Geyser Basin
Great Fountain and White Creek Group

Great Fountain Geyser sits in the middle of one of the prettiest sinter formation in the park. The sinter forms a series of terraced concentric reflective pools around the geyser's 16' diameter vent. Even if the geyser isn't erupting, it is worth driving past to see the pools. They make a very pretty picture at sunset.

Great Fountain is a fountain-type geyser. Its interval range from 9 to 15 hours but its short term average interval is usually stable enough that the eruptions can be predicted to within an hour or two. Great Fountain's maximum height ranges from about 75 feet to over 220 feet. Its duration is usually about one hour but durations of over two hours have been seen.

Great Fountain is a major geyser but many people, when hearing it erupts to over 200 feet, are disappointed by its more common maximum of less than 100 feet. For this reason, Great Fountain has earned a number of pejoratives, such as The Great Flounder. The smaller eruptions of Great Fountain are still large and pretty but pale in comparison to the truly large eruptions. It is the hope of seeing one of the rare but spectacularly large eruptions that tends to bring the geyser gazers back to Great Fountain time after time.

Great Fountain erupts in a series of distinctly spaced bursts. The first group of bursts lasts about ten minutes. Then there is about a five minute quiet period followed by another five or so minutes of activity. These quiet and active episodes continue until the end of the eruption. There can be over seven active periods in the eruption. Usually the first period of activity is the tallest and strongest, with the first and sometimes the second burst being the strongest of the eruption. Sometimes, the largest burst will occur during the third active period. This especially seems to happen when the first period has been uninspiring. Rarely, large bursts will continue long into the eruption. There have even been a few reports of 100 feet plus bursts in the fifth and sixth periods.

Great Fountain has two types of truly spectacular behavior. A Superburst is an exceptionally tall burst of water, over 150 feet. Some superbursts have reached 230 feet. Superbursts, when they occur, are usually the first burst of the eruption but they have been know to sometimes occur later in the eruption. A Blue Bubble occurs when a calm and still pool of water is domed up by a large expanding steam bubble. As the steam bubble rises and expands, the entire 16 foot wide pool of water is lifted and domed outward creating a beautiful blue bubble. Once the steam reaches the surface the water explodes outward and upward. Blue bubbles most commonly occur at the start of the eruption but the have been known to occur at the start of other active periods, especially the third. A fair number of blue bubbles result in a superburst but not all.

Great Fountain sometimes goes through a Wild Phase. During a wild phase, Great Fountain seems to forget how to end an eruption. Ten to fifty foot play continues for hours to days. Once the play finally ends, Great Fountain usually takes a few days to recover before returning to "normal" eruptions. Interestingly, wild phases mainly occur late in the year.

What to look for:
Great Fountain begins overflowing from its crater into the basins around the vent about 70-100 minutes prior to the eruption. Great Fountain has been known to start overflowing and then stop a short time later. These false overflows can not be used to predict the eruption. Once the overflow starts, you need to wait a few minutes to be sure that the overflow continues. Once you are sure that the overflow isn't going to stop, then you can use the 70-100 minute window to predict the geyser accurately.

About 30-60 minutes after the overflow starts, small bubbles will appear in an arc along one edge of the pool. This boiling slowly grows in intensity and the arc continues to grow until it finally forms a circle of boiling completely around around the edge of the pool. The boiling continues to periodically grow until there is a one meter tall boil. For timing purposes, this is the official start of the eruption. The bursting play may start immediately after the one meter boil or it may wait for a few minutes before starting. The time between the first one meter boil and the first burst is called the pause. If you are fortunate, the geyser may go completely quiet during the pause. While it may be nerve wracking to see the pool quiet like this for as much as nine minutes, it is a good omen. Blue bubbles form best when the pool is calm and some people feel that a quiet pause is also a good omen for an exceptionally tall eruption. While I can understand the logic behind the blue bubble claim, I'm not sure about the height claim.

The first few bursts usually pour out a lot of water. It is fun to watch the wave of water as it spreads out and then tumbles over the concentric terraces of the sinter formation.

Determining the end of the eruption is hard. Just when you think it has had its last active period, it will throw in another. But, eventually it does end.

The geyser refills quickly. Noisily boiling water can be seen a few inches down in the pool shortly after the eruption. If you've just arrived at the geyser, be careful not to confuse this post play boiling for the preplay boiling. This can be problematic when conditions are steamy. The post play boiling occurs while the geyser is below overflow. The preplay boiling occurs after the geyser is in over overflow. The post play boiling will continue for a couple hours after the eruption. Finally the pool will become calm again and then start to slowly rise as it prepares for the next eruption.

Electronic Monitor Files
Great Fountain eruptions for 1999.txtGreat Fountain eruptions for 2000.txt
Great Fountain eruptions for 2001.txtGreat Fountain eruptions for 2002.txt
Great Fountain eruptions for 2003.txtGreat Fountain eruptions for 2004.txt
Great Fountain eruptions for 2005.txtGreat Fountain eruptions for 2006.txt
Great Fountain eruptions for 2007.txtGreat Fountain eruptions for 2008.txt
Great Fountain eruptions for 2009.txtGreat Fountain eruptions for 2010.txt
Great Fountain 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  

Great Fountain Geyser has been monitored using electronic data loggers since 1999. The record is not complete for these years but there is a substantially complete record from 1999 to date with few large gaps during winter months when critters damaged the loggers or we were not able to access the loggers because of bear management closures. The first gap is from 5 March to 15 June 2000, the next from 2 to 23 January 2004, then from 31 March to 31 May 2004, then from 7 November 2004 to 13 July 2005. There were a few short breaks of a day or two also.

The sensor for Great Fountain is located in one of the runoff channels about 50 meters from the vent, so the electronically recorded start times are two to four minutes later than visually obtained times. For statistical purposes this does not matter since the time between eruptions is not affected. The sensor easily detects the temperature rise signifying the wave of hot water resulting from the eruption start, but the individual bursts and the eruption duration are not distinguishable on the electronic record.

Electronic times are recorded to the nearest minute during the summer season (that is, while I am resident at Old Faithful, usually from mid-June to late September). During the winter sampling times have varied from two to three minutes. Starting in the winter of 2005-6 and also for the winter of 2006-7 we used two loggers and sampled at three minute intervals. For some of the earlier summer season deployments sample intervals 30 seconds were used.

A new type of logger capable of recording temperatures every minute for several months was deployed in late September 2008 with a sample rate of 1m06s and that rate is being continued for the summer of 2009, and thereafter. In the spring of 2011 there is a gap of a few weeks because of my late arrival in Yellowstone.

Activity in 2011  
The statistical summary for 2011 is available at Great Fountain Geyser 2011 Statistics. A pdf of the same information is available at Great Fountain Geyser 2011 pdf

The activity of Great Fountain Geyser for 2011 to date is shown in the graph at the right. The graph is updated weekly during the summer months. The blue line shows all of the eruption intervals and the yellow line shows the 1-week moving median interval.
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The Great Fountain activity for the three months prior to the last data download is shown in the next graph.
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The activity for the month prior to the last download is shown in the third graph at the right. The current year graph shows longer term trends while the other two shorter timeline graphs give a better sense of the most recent activity.
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Another useful representation of a geyser's activity is the distribution of intervals. The next chart shows the distribution of intervals for 2010 to date (blue), the most recent month of data (magenta), and the most recent week of data (yellow). This chart illustrates the range of intervals that necessitates the four hour prediction window. Note that in this and the other 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 30 minutes. The bar appearing above the label "8:30," for example, contains intervals from 8h01m through 8h30m.
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The next graph shows the Great Fountain Geyser interval statistics by month. This graph shows the maximum, mean, median, and minimum intervals for each month for which data is available. This chart summarizes the range and gives another perspective on the activity. The minimum value is an indication of how soon after the previous eruption one must arrive at Great Fountain to be (relatively) sure to see the next eruption and the difference between the minimum and maximum suggests how long the wait could be.
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The prediction results graph shows how the current prediction would have fared if applied over the past week and month. This graph shows the percent of all intervals that fall below the prediction window, in each quarter of the window, and the percentage of intervals that are longer than the window.

Please note that the prediction used to construct this graph uses only the time of the eruption and a standard prediction time. Actual predictions posted at the Visitor Center and at Great Fountain Geyser for much of the summer are adjusted based on observation of the duration of the eruption and the start of overflow, if known, and may be more accurate than this graph indicates.

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Activity since 1999  
One way to present the eruption interval data is to graph the interval as a function of time. The graph shown at the right shows all of the electronically recorded intervals since 1999.
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The graph of all intervals shows a wide variation. A better idea of trends in intervals can sometimes be seen by plotting a moving median value. The graph at the right shows the one-week moving median intervals for all the data since 1999.
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The final graph, shown at the right, gives Great Fountain's interval statistics on a month by month basis, including the maximum, minimum, mean, and median intervals for each month. The very short (~4 hour) minimum intervals indicate periods of "wild phase" activity, during which Great Fountain has continuous low intensity activity for many hours. The short intervals occurred before and after the wild phase activity.
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Activity in 2010
Activity in 2009
Activity in 2008
Activity in 2007
Activity in 2006

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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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