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Geysers of the World   

Geysers of Yellowstone   



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

Upper Geyser Basin
Grand and Castle Group

Grand is a fountain-type geyser. Its interval is usually around 6 to 15 hours (the average has been about 7 to 8 hours for the past two years). Its height is about 150 to 180 feet and its duration is about 9-12 minutes. It will sometimes stop after about 8 to 9 minutes and then restart after a minute or so. This second "burst" and any subsequent bursts are often among the tallest if not the tallest of the eruption. About half the eruptions had more than one burst in 2005. Be sure to wait to see if there is a second burst.

Grand Geyser is closely connected to many of the geysers in its immediate vicinity. It is most easy to see this connection in Vent Geyser and Turban Geyser.

Vent Geyser usually only starts an eruption immediately after the start of a Grand eruption. On rare occasions Vent can start just before Grand. Vent almost always erupts in conjunction with Turban Geyser. Vent and Turban will continue to erupt for about an hour after Grand erupts. Then Vent and Turban stop and Vent usually does not erupt again until the next eruption of Grand. (In some seasons Vent and Turban have started another long eruption, lasting up to another two to three hours.) Occasionally Vent will erupt concurrently with Turban during the first Turban eruption following the hour long Vent and Turban eruption that starts with Grand's eruption. On extremely rare occasions Vent has erupted by itself.

During the hours prior to an eruption of Grand, Turban Geyser erupts about every 20 minutes for about five minutes. During Grand's eruption, it will erupt continuously often increasing in size from its normal 5-10 feet to about 20 feet. For the hour or so after Grand's eruption Turban erupts continuously with Vent Geyser. Turban then resumes its about 20 minute cycles.

What to look for:
First, it is easy to get confused when looking for Grand Geyser. The Park Service has put out a sign to help you but the first thing most people notice is the large raised rim around Turban Geyser and they miss the large flat pool just to the right of Turban. This large pool, with almost no rim, is Grand Geyser. When Grand Geyser finally erupts, it does so just before the start or within one, or rarely two, minutes after the start of a Turban eruption. If Grand doesn't start at this time, you'll have to wait for the next eruption of Turban and hope. After an eruption of Grand, Grand's pool is empty. Water slowly fills the pool and reaches first overflow about 5 hours after the eruption. Once in overflow, it can be noted that the pool rises and falls in approximately 20 minute cycles. These cycles correspond to the eruptions of Turban Geyser. At about the time an eruption of Turban starts, the water in Grand will usually begin to slowly drop and will continue to drop as Turban erupts. Once Turban stops, the water in Grand will slowly begin to rise again. With some practice, a good eye and favorable weather conditions, you may be able to see these drops and rises. Look around the front edge of the pool and you will notice some slightly raised sinter formations. At high water they form small islands or may even be covered by the water, at low water they will stick out of the water by about an inch. What you are looking for is for the water to stay high at the time you expect Turban Geyser to erupt. If this happens, you then want to look for large ripples (called waves) on Grand's pool. These waves are hard to see. It often takes practice to see them. Once large waves start while Grand's pool is staying full, you are almost assured of an eruption. The eruption will start just prior to Turban or within a minute or so of Turban. If it doesn't erupt within this period, sit back and wait for the the next Turban eruption.

Once Grand erupts, there is the possibility of more than one burst. A Grand burst is defined as continuos eruption of water from Grand. The shorter this first burst, preferably less then 10 minutes, the more likely it is that you will see a second, third or more bursts. (The most bursts seen in one eruption during the last few years is 11 bursts but the average is usually between 2 and 4 bursts.) After a burst has ended, watch Grand's pool. Sometimes the water will be out of sight, sometimes it will still be visible. Watch to see if the water rises. If the water rises and begins to bubble be prepared for a spectacular sight as Grand erupts to its full height in one continuous motion. If the water drops, well, there's always the next eruption.

Electronic Monitor Files
Grand eruptions for 1999.txtGrand eruptions for 2000.txt
Grand eruptions for 2001.txtGrand eruptions for 2002.txt
Grand eruptions for 2003.txtGrand eruptions for 2004.txt
Grand eruptions for 2005.txtGrand eruptions for 2006.txt
Grand eruptions for 2007.txtGrand eruptions for 2008.txt
Grand eruptions for 2009.txtGrand eruptions for 2010.txt
Grand 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  

Grand 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 2002 to the fall of 2008 with only a few gaps.

A gap from 20 to 31 January 2008 resulted from a sensor failure. A gap from 1954 on 24 May to 1054 on 27 May due to memory filling.

The Grand logger failed after the 6 November download. Some data from a second logger are available after 6 November 2008 but there are numerous gaps.

Activity in 2011  
The overall statistics for 2011 are shown at Grand 2011 Statistics. A pdf of this summary is at Grand Geyser Recent Activity Summary.

The activity of Grand Geyser in 2011 is shown in the graph at the right. The blue line shows all of the eruption intervals and the yellow line shows the 1-week moving median interval. The graphs for the current year are updated about every six weeks from October to June and weekly from June to the end of September.
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Grand Geyser's activity for the recent past is shown in the next graph, and the activity for the past month in the third graph below.
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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 the whole of 2011 to date, the most recent month of data, and the most recent week of data. 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 15 minutes. The bar appearing above the label "8:15," for example, contains intervals from 8h01m through 8h15m.
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The monthly statistics graph shows the maximum, mean, median, and minimum intervals for each month. 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 Grand 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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Another slant on this is shown in the prediction graph which shows how the current prediction would have fared as 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.
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Activity since June 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. The gaps in 1999, 2000, and 2001 are many weeks long and resulted from the logger filling during times that the Park is closed. We were somewhat more successful since then, but in the winter of 2004-5 there were technical problems with the logger.
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The interval graph shows the large variation in interval from one eruption to the next. A better idea of the change in intervals over time can be seen from the graph of the 1-week moving median intervals, shown at the right. Grand has experienced a decrease in intervals over the time shown. In 1999, 2000, 2001, and 2002 there were brief (2 to 3 week) periods of short intervals, more clearly shown on the moving median graph than on the interval graph, but in all of these cases Grand soon reverted to its long-term behavior. However, following the several week short (about 7 hour) interval series in mid-2002 although Grand reverted to 11 hour intervals in August a gradual and steady decline in intervals began which continued until March 2003, then another decline started in late 2003 that continued until Grand’s weekly moving median dropped below 7 hours in August 2004. Moving median intervals have remained in the 7-8 hour range since with little change.
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The graph at the right shows Grand's interval statistics on a month by month basis, including the maximum, minimum, mean, and median intervals for each month. Note that before 2005 the mean interval was roughly halfway between the minimum and maximum for each month, but since early 2005 the mean has been closer to the minimum. This was because most intervals were short and there were few intervals near the maximum.
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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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The above photograph shows an afterburst of Grand. Afterbursts occur from an empty crater up to about ten minutes after the end of the eruption. Afterbursts are relatively rare. Also shown are Vent and Turban Geysers during their post Grand activity.

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The above picture shows afterplay from Vent and Turban. Notice Grand's empty crater to in the lower right portion of the picture.

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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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