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  Riverside Geyser
Feature Type: Geyser
Geyser/Spring Type: Cone geyser

Upper Geyser Basin
Grotto, Riverside, Chain Lakes

Riverside is a cone-type geyser. Its interval is usually 5 1/2 to 7 hours, its height about 75 feet and its duration about 1/2 hour. The water phase of the eruption lasts about 20 minutes and is followed by a steam phase. Situated on the bank of the Firehole river at the base of a wooded hill, Riverside has one of the most picturesque settings of any geyser. Riverside's eruptions are highly bi-modal. Eruptions usually occur either about 1/2 hour before or 1/2 hour after the current average. No one know how to determine which of these two, the short interval or the long interval, will occur. If this could be determined, Riverside would be one of the most predictable geysers in the park.

What to look for:
You watch Riverside from a viewing area across the Firehole river from the geyser. From this position, Riverside's formation looks something like a chair. There is a vent high up on the back and another vent in the seat of the chair. Except for some minor splashing, the geyser erupts from the lower vent in the seat of the chair. About 1 1/2 to 2 hours before the eruption the main vent in the seat of the chair begins to overflow into the river. This overflow is variable. About an hour later, the small vents behind the main vent will begin to bubble and boil. The activity fluctuates but seems to build as time progresses. Finally a splash or two will be seen in the upper vent at the top of the chair back. One of these splashes from the upper vent will be large enough to spill water into the river, this usually starts the eruption.

Electronic Monitor Files
Riverside Geyser eruptions in 2005.TXTRiverside Geyser eruptions in 2006.TXT
Riverside Geyser eruptions in 2007.TXTRiverside Geyser eruptions in 2008.TXT
Riverside Geyser eruptions in 2009.TXTRiverside Geyser eruptions in 2010.TXT
Riverside Geyser eruptions in 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  

Riverside Geyser has been monitored electronically using data loggers since 2000. This geyser is a visitor favorite, with regular eruptions lasting 20 minutes or so and a beautiful setting. We have had mixed success in monitoring the activity, however. The sensor is located so that it picks up the water temperature in the pool that forms around the vent when overflow starts. This gives both overflow duration and eruption start information (the latter inferred by the drop in temperature caused by the cessation of overflow once the eruption starts). Since the geyser is a cone-type geyser with almost all of the eruption water landing in the Firehole River, the sensor is not able to record eruption durations.

Over-winter logging has been problematic because of the difficulty of access to the geyser with snow and ice, and because our original logger location was covered by a thick layer of ice. Another nagging problem has been the displacement of the sensor from the pool which makes the temperature trace difficult or impossible to interpret. The result of all of the difficulties is a fragmentary record, which was still the case in 2006. In the winter of 2006-7 we were successful in obtaining over winter data at last. In 2007-8 we were unable to download the data for one six-week interval due to heavy snow cover. Over the winter of 2009-2010 we were successful with the exception of November, when a logger problem resulted in a month-long gap in data.

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

I have also included statistics on the duration of overflow and the time from the start of one eruption to the start of the subsequent overflow. The reason for these statistics is discussed later in this article.

The interval graph shows all of the intervals for 2011. The blue line shows the interval data, and the green line shows the moving median interval. The range of intervals spans about 50 minutes for most of the year. This is, as we will see, the result of Riverside's switching between two different intervals. The yellow line represents the time between the start of each eruption and the start of the following overflow. The orange line is a plot of the overflow length.

Note that the overflow length (the orange curve) looks much like the interval plot. This is because almost all of Riverside's variation is in the length of the overflow portion of the cycle. Eruption durations are within a minute or so of 20 minutes. The quiet time is shown to be around 4h32m (see the statistics referenced above). The quiet time is very consistent with a standard deviation of just 3m37s for all of the data shown, and just 2m58s for the last month of data. The red lines are linear regression fits to the interval data, which I include to give a sense of the trend in eruption times.

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The next graph gives just the data for the past three months. The Y-axis scale is expanded to show the interval characteristics more clearly. It is more apparent that the intervals are either short (around 6h0m) or long (around 6h40m), with few intervals falling between these values. The quiet time, shown in brown at the bottom of the graph, is consistently between 4h20m and 4h40m.

The red dashed lines show the limits of the prediction window used by the NPS to predict the next eruption.

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The interval histogram illustrates the bimodal nature of Riverside's intervals quite nicely.
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The second interval histogram plots the same data in one minute buckets, which shows the bimodality more clearly.
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The companion plot of overflow length shows very nearly the same shape.
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With the regularity that Riverside exhibits, predicting the next eruption would seem simple. And it is, provided the time of the previous eruption is known. The graph at the right shows the prediction results assuming that each eruption start time been known. The predictions are made using an interval of 6h05m, which is midway between the two modal peaks of 5h48m and 6h26m. Since Riverside is bimodal, however, and the modes are typically 40 minutes apart, this means that the eruptions never happen at the predicted time, but are either "early" or "late" depending on whether the overflow is long or short!

Since the modes are only 40 minutes apart, this does not represent a big problem if the previous eruption time is known. Until the first eruption of the day is seen, however, predictions have to be made using double or triple intervals, which leads to much uncertainty, especially when Riverside is "stuck" in either long interval mode or short interval mode.

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Activity since 2000  
Riverside is known for its regularity. It is also known for being "bimodal"; that is, it has two different intervals at which it likes to erupt and switches between the two intervals. This effect is visible in the overall plot of interval vs time, shown at the right.
There has been some variation in the intervals, but they generally lie between 5h30m and 6h50m. Since July of 2003 there has been little change in Riverside's activity and intervals have remained largely between 5h50m and 6h50m.

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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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This vintage Detroit Publishing Co. post card of Riverside Geyser, from the early 1900s, shows the geyser from a vantage point no longer accessible to the park tourist. Note the stagecoach on the old bridge just down stream from the geyser. The bridge has since been moved about 150 yards further down stream, so it know crosses the river near Fan and Mortar Geysers.

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

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