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Geysers of the World   

Geysers of Yellowstone   



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

Upper Geyser Basin
Giant Group

Oblong is a major geyser. It is not too tall, usually the maximum height is around 25 feet but in exceptional eruptions it has reached 50 feet. What makes it a major geyser is the amount of water it puts out during its 5 minute eruption. Because the water flows almost directly into the Firehole river, it is not possible to measure the amount of water expelled during an eruption but it is estimated at over 10,000 gallons. That is a little more water than is expelled during a large eruption of Old Faithful.

Oblong was named for the shape of its large oblong shaped pool. While technically a fountain-type geyser, Oblongs eruptions can't really be classified as bursting type eruptions. The eruptions are more like a very large and heavy boiling that covers the pool and raises the water in surges of 25 feet or more.

Oblong's intervals have ranged from 3-12 or more hours. It is also known to go dormant for months at a time. The duration of its eruptions is about 5 minutes. Oblong has been known to have a series of two to three eruptions on rare occasions with intervals as short as 30 minutes. The latter eruptions in the series occur from a low pool.

When active, Oblong can often be fairly predictable based upon its current short term average.

Connection to Giant Geyser:

Oblong is definitely connected to Giant Geyser. Oblong has almost always erupted within a few hours of Giant. In early 1997, when Giant was fairly frequent and Oblong was nearly dormant, the only eruptions seen from Oblong occurred a few hours after Giant had erupted.

What to look for:
When active, which in the past few years has seemed to be less than half the time, Oblong follows a fairly regular pattern as it builds to an eruption. After an eruption, the pool is down and not visible from the boardwalk. It may take up to 3 hours for the pool to refill. Once the pool is full and overflowing, the pool will eventually start having 20 minute cycles of rising and falling. At the high end of the cycle the pool overflows, at the low end it is an inch or two below overflow. Oblong erupts when the pool overflows and the overflow becomes quite a bit larger than normal. This increase in overflow is only noticeable if the geyser has been kept under close observation. Once you get practice, it becomes fairly easy to determine if it will erupt on the current overflow. The heavy overflow lasts for a number of minutes. If you are sitting very still on the boardwalk and there are no people walking anywhere else on the boardwalk, you will eventually start to feel thumping from Oblong as steam bubbles collapse at depth in the geyser. At this point, Oblong is very close to starting. Oblong will continue thumping throughout the eruption with the thumping getting stronger as the eruption nears the end.

When inactive, Oblong steadily overflows with little or no discernible change in the level of the pool. After a period of time, because the hot water from the eruptions is no longer killing it off, the cyano-bacteria mats in Oblongs runoff channel start growing larger and turning orange.

Electronic Monitor Files
Oblong eruptions in 1997.txtOblong eruptions in 1998.txt
Oblong eruptions in 2001.txtOblong eruptions in 2002.txt
Oblong eruptions in 2003.txtOblong eruptions in 2004.txt
Oblong eruptions in 2005.txtOblong eruptions in 2006.txt
Oblong eruptions in 2007.txtOblong eruptions in 2008.txt
Oblong eruptions in 2009.txtOblong eruptions in 2010.txt
Oblong 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  

Oblong Geyser has been monitored electronically intermittently in 1997 and 1998, and then every year since 2001. The sensor for Oblong is located on the edge of the large sinter platform in a location that receives runoff water reliably in warm weather. However, in the wintertime sometimes the sensor becomes encased in ice when there is very low air temperature and long times between eruptions. Therefore, the interval data for December through March sometimes has long intervals that may include eruptions that were undetectable because the sensor was icebound. In many cases it is possible to detect a small temperature rise, but when looking at the analyses in this section keep in mind that there are potentially eruptions in the long intervals that were missed.

In other cases the sensor is moved by the force of the water making subsequent eruption detection difficult.

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

Since early 2007 Oblong has been remarkably consistent in its intervals. Many of the very long and very short intervals occurred near the time of a Giant Geyser eruption.

The long (>8 hour) intervals in January-March are almost certainly due to ice dams keeping the hot water from the sensor.

The interval graph shows all of the intervals to date for 2011. 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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The graph at the right shows the intervals for the 3-month period preceding the last data download.
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The next graph shows interals for the last month for which data is available.
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The histogram of intervals shows a broad peak between 3h30m and 6n30m hours in the year-to-date (blue) bars. 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 "3:30," for example, contains intervals from 3h01m through 3h30m.
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The final graph for the current year is the monthly statistical summary.
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Activity since 1997  
The graph at the right shows the Oblong data since 1997. Oblong's activity remained substantially the same since the first electronic data available to me, from 1997. Beginning with the summer of 2002 we have substantially continuous coverage, and this shows a tendency to much more long interval activity in the winter months.

As noted before, some of this may be due to ice around the thermistor, but many of these long intervals are not ice-affected and represent the actual behavior of the geyser. Since April of 2006 Oblong's intervals have been shorter and more consistent, largely between three and six hours.

Click for a larger image

The next graph shows the moving median interval, where the median was computed on approximately a weekly basis. The actual moving median computation was done each year by finding the average number of eruptions per week and using that number as the range for the median.
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The final graph in this section plots the monthly minimum, mean, median, and maximum interval for those months for which data is available. Minimum intervals are consistently in the 2h to 3h range (except for January 2005, when a few series of eruptions about an hour apart occurred).
Click for a larger image

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

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

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