Giant Group,   Daisy Group

  and  

Grotto Group 

[ Giant Group - Map ] [ Daisy Group - Map ]
[ Grotto Group - Map ]

Giant Group: - Map

The Giant group was often almost completely ignored during the long years from 1956 to 1996 that Giant Geyser was dormant or infrequent. The only major geyser to be seen in the group for most of this time was Oblong Geyser. In 1996 that started to change. All it took for many geyser gazers to get interested in the group was to either see an eruption of Giant Geyser or to know that an eruption of this superlative geyser was possible. In July 1996, Giant Geyser started one of its best periods of activity ever seen and its best activity since 1955. Between July 1996 and January 1998, the longest interval was two months. By the fall of 1997, intervals were between 3.5 and 5 days. As of this writing, the activity is still continuing.

Giant Geyser connects into all of the geyser of its group. It also connects to the Grotto Group and possibly to the Daisy Group.

Bijou Geyser: [Map]

Bijou Geyser erupts almost continuously. Because of this, early park visitors often called it Young Faithful Geyser. Unlike most geysers, the excitement at Bijou occurs when it stops. Actually Bijou's eruptions are fairly nice. The eruption can reach 15 feet and sometimes the eruption changes into a nice steam phase. Still everyone watches for Bijou to stop because this is when you may get a Giant Hot Period. Not all Giant Hot Periods result in an eruption of Giant but all Giant eruptions are preceded by a Giant Hot Period.

What to look for:

Ultimately the reason to watch Bijou is in the hopes of seeing a Giant Hot Period. Thus the observer is looking for a two or more minute stop in Bijou's activity.

Bijou stops for three different reasons:

First - Bijou stops during Giant's eruptions and does not restart until the system has started to recover from the eruption. The amount of time it takes for the system to recover can vary greatly but it usually takes over eight hours for the system to recover to the point that Bijou restarts.

Second - About five to six hours into a long mode eruption of Grotto Geyser (a Marathon eruption) Bijou will slow down and eventually stop. Bijou usually recovers and restarts about 4-6 hours after Grotto stops. During periods of frequent hot periods, Giant will often have a hot period at about the time that Bijou recovers.

Third - Bijou can have a PAUSE in its activity. A pause occurs when all splashing from Bijou stops. Assuming that Bijou is not pausing for either of the first two reasons, the reason that Bijou pauses is because the water levels on the Giant Platform are rising. The initial stages of the rising water can be hard to see from the boardwalk but Bijou's Pause indicates the rising water levels. Eventually, if the pause lasts long enough, the rising water levels can be seen in Mastiff Geyser and if a hot period results, in the many platform vents.

Catfish Geyser: [Map]

Catfish Geyser often erupts for short periods of time to about 10 feet. These small eruptions can occur during a Giant Hot Period but do not seem to have much significance to the Hot Period. They also occur outside of the Hot Periods. For the most part none of these eruptions are too inspiring. This can all change, though, during a Mastiff Function eruption of Giant Geyser. During some Mastiff Function eruptions, Catfish will join Mastiff and Giant in the eruption and erupt in a narrow jet for as many as 5 minutes and up to 75 feet tall.

Giant Geyser: Click for more information.

Mastiff Geyser: [Map]

At times, Mastiff has frequent boiling and splashing "eruptions" These "eruptions" are usually very small but sometimes reach 5 feet. For the most part, this activity signifies little and goes virtually unnoticed. What is noticed though is Mastiff's role in Giant's Hot Periods and in Giant's Mastiff Function eruptions.

Mastiff Geyser plays a key role in the observation of a Giant Hot Period. From the boardwalk, it is possible to see a short distance into Mastiff's front vent. This vantage point makes it possible to see if water is rising during a Bijou pause. As the water rises, it forms a slowly rising pool in Mastiff. This pool is easily distinguished from the splashing that is sometimes seen in Mastiff's front vent. If at any time, the pool drops and does not rebound, the hot period is probably doomed to end without an eruption from Giant. As long as the pool stays up, the eruption is possible. As the water rises, if this is going to be a hot period, eventually, some of the platform vents will start overflowing and at least one will start erupting. The water in Mastiff may continue to rise and start to overflow. Depending on the strength of the hot period and Mastiff's contribution to it, Mastiff may continue to rise. The overflow can become very large. Mastiff may start surging from its two vents. These surges can reach the height of Giant's cone, about 12 feet and yet the hot period may still end without an eruption. On the other hand, if this is a Mastiff Function eruption of Giant, Mastiff will eventually start to erupt. Mastiff's two vent erupt differently. One erupts in a massive vertical column while the other erupts less massively at an angle. Surprisingly, considering the two vents can be seen to be connected a short distance below ground, the two vents do not always erupt together. Mastiff's eruption reaches over 35 feet in height and has been known to reach a very impressive 125 feet. Mastiff usually lasts less then 5 minutes and ends just before Giant reaches its full height. A Mastiff Function eruption of Giant is one of the most spectacular eruptions to be seen in Yellowstone National Park.

Oblong Geyser: [Pictures] [Map]

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 takes about 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.

Platform Vents:

The Platform Vents are small vents located on Giant's platform in front of and to the right front of Giant's cone. There are approximately 11 platform vents. These small vents are very hard to see except when they are overflowing or erupting. The vents erupt during Giant's Hot Period. Giant erupts only during a hot period but not all hot periods result in an eruption of Giant. The build up of a Hot Period starts with water levels rising in the system. The first manifestation of this to be seen is usually a Bijou Pause followed by rising water in Mastiff. Then water will start overflowing from some of the platform vents. It only takes one vent to erupt for there to be a hot period but most eruptions that lead into an eruption of Giant involve a number of the platform vents. Eruptions from the platform vents range from a few inches from the shortest to about 10 feet from the tallest.

The Hot Period can last from a few minutes to about 15 minutes. One of two things happen at end the hot period. Usually the water level in Mastiff drops and the hot period fizzles. But sometimes, Giant erupts and the hot period ends during the eruption.

Purple Pools: [Pictures] [Map]

The Purple Pools, there are three of them, are located across the river from Giant. Usually, the most that can be seen from the boardwalk is the steam rising from them and their runoff channels. On a few very rare occasions, they have been known to erupt. On September 21, 1998 South Purple Pool was seen erupting in what proved to be the first of a handful of eruptions seen that season that ultimately included all three Purple Pools. On October 11, 1998 all three Purple Pools erupted. North to an estimated 60 to 80 feet, South to 20 to 30 feet and East (middle) to 15 feet.

Another note of interest concerning the Purple Pools is that they are connected to Giant Geyser. An eruption of Giant causes the pools to drop about one foot.

Turtle Geyser: [Pictures] [Map]

Turtle Geyser is a very rare geyser. It is located on a separate mound of sinter a short distance to the right of Giant's Platform. The separation appears to have been caused by erosion. Turtle was seen to have a couple of eruptions by itself to about 20 feet in 1956 at the end of what was Giants most active episode during the history of the park. Since that time until 1997, the most Turtle was seen to do was to overflow during some Giant Hot Periods. Twice in the fall of 1997 during Giant Normal Function eruptions, Turtle was seen to erupt to about 2 feet.

Daisy Group: - Map

 [Daisy Group introduction provided by Kyle Chumbley.]

The Daisy Group contains numerous geysers that have seen activity fairly frequently, but not all are consistently active. Daisy Geyser is often one of the most predictable geysers in the park, although at times other springs in the group may steal Daisy’s thunder. The major geysers of the group are: Daisy and Splendid. Other geysers include Comet, Bank, Radiator, Daisy’s Thief.

Splendid is largest geyser in the group, but it is seldom active. Thus, Daisy is usually the largest active geyser in the group. When Splendid is active, Daisy may either become dormant, unpredictable, or continue to play along with Splendid. Three other pools in the area are noteworthy: Bonita, Brilliant, and Murky Spring. The Daisy group is probably connected to the Giant group.

Brilliant Pool: [Map]

Brilliant Pool, which is located directly south of Comet Geyser, is connected to Daisy and Splendid geysers. This connection is most easily seen during an eruption of Daisy. Prior to Daisy, Brilliant Pool is full. As Daisy erupts, the pool begins to drop. By the end of the eruption, the pool has dropped a few inches. The pool then refills with Daisy.

During a Splendid eruption Brilliant Pool drops further than it does during a Daisy eruption. If Splendid is having a series, Brilliant rarely refills completely prior to the next eruption. Thus, the pool can continue to drop further and further after each eruption. After especially large Splendid eruptions or after Splendid/Daisy Dual eruptions, Brilliant can drop far enough that it can erupt on its own. These eruptions occur in a series with each eruption lasting a few seconds and being spaced apart by about two minutes. The series only lasts a few minutes. These rare eruptions are often short, with some only breaking the surface, but some can reach over 15 feet.

Brilliant Pool, at times, has had a detrimental effect on Daisy. In the early 1950s, for instance, Brilliant started overflowing heavily and Daisy went dormant.

Comet Geyser: [Map]

Comet Geyser sits in the middle of, and has the largest cone of, the Daisy Group. Because of this and its almost constant play, many first time visitors to the group, mistakenly assume that Comet is Daisy.

Comet splashes almost continuously. Every few minutes the surging becomes larger and may reach as much as six feet but that is about all that Comet does. After large eruptions of Splendid and sometimes after Daisy, Comet will appear to slow down and get shorter but it rebounds quickly. Thus, like almost everything else in the group, Comet appears to be connected to these two geysers.

There have been a handful of reports throughout the history of the park of Comet erupting to as much as 30 feet. Concerned that the observer may have confused Daisy and Splendid, which has happened many times, many look upon these reports with skepticism. Even so, I wouldn't be too surprised if Comet doesn't have a rare eruption every once in a while.

Daisy Geyser: Click for more information.

Splendid Geyser: Click for more information.

Grotto Group: - Map

It is always fun to sit waiting for the start of Grotto Geyser and hear tourists walk by and comment on Grotto's intriguing cone and say that the geyser must be dead only to return from their walk to see Morning Glory and discover that not only is Grotto erupting but also Grotto Fountain, South Grotto Fountain and Rocket Geysers. The Grotto Group is always full of surprises. These surprises and the fact that many of the groups geysers are beautiful in their own right makes the Grotto Group an interesting area to observe.

The Grotto Group is one of the most complex groups in the Upper Geyser Basin. Most, if not all of the geysers and pools in the group are connected. The group is also connected to Giant Geyser. These connections make for complex interactions between all of the connected geysers. The information below is intended only as an overview of the group. Discussing all of the interactions and possibilities is beyond the scope of this presentation.

While the Grotto Group may be complex, it is still accessible. Most of the interactions can be easily seen and understood and yet, there is also subtlety here that takes time to see and understand. Because of the ease of first seeing the geyser connections and the further challenge of seeing the subtlety, the Grotto Group is a good choice for the novice that wants to try his or her hand at understanding a geyser group and its interconnections.

Grotto Geyser: [Pictures] [Map]

Grotto Geyser is the namesake of the group. It was named and first reported on by the Washburn expedition of 1870. While not tall, the maximum height, usually reached at the very start of the eruption, is only 30-40 feet, the eruption can last for a fairly long period, expelling large quantities of water. Grotto is a fountain-type geyser. The pool through which it erupts is hidden inside Grotto's unique sinter formation. The unique formation is the result of sinter coating old tree stumps that stand around the pool. The result is a shell like formation that is not seen anywhere else in the park. Grotto's sinter formation connects directly to the large raised rim of Rocket Geyser. Both geysers erupt simultaneously.

The duration of the eruption can be anywhere from one hour to 26+ hours. Eruptions are often classified as one of two types. Short Mode eruptions usually last for 1-2 hours but can last longer. These eruptions are usually but not always concluded by a major eruption of Rocket Geyser. About 3/4ths of Grotto's eruptions are short mode eruptions. Long Mode eruptions, sometimes called Marathons, generally last for 6-12 hours but occasionally can last considerably longer. These eruptions usually do not include a major eruption from Rocket Geyser but do include eruptive activity from Spa Geyser. Also, during Long mode eruptions, the water level in Marathon Pool often drops a few inches. When the Short and Long mode classifications first came into common use, intermediate length eruptions, 3-6 hours, were very rarely seen. Since then, these intermediate eruptions have become more common. No consensus has yet been reached on how to classify these intermediate length eruptions.

Grotto's interval depends on the duration of the previous eruption. The interval for short mode eruptions is usually around 7 hours. The interval for long mode eruptions can be over a day. The longer the previous eruption, the longer the next interval. Fortunately, even if you don't know the length of the pervious eruption, with a little practice, it is usually possible to determine if the start of an eruption is imminent.

What to look for:

In recent years, most eruptions of Grotto Geyser have been preceded by Grotto Fountain Geyser. Thus, look at the information for that geyser to understand what to look for. Even if Grotto is not preceded by Grotto Fountain, the things to look for are still basically the same.

Predicting Grotto Geyser:

Lew and Jan Johns have been studying Grotto Geyser for a number of years. They have determined that you can predict the next eruption of Grotto based upon the duration of the current eruption. Follow this link to read their report on using eruption durations to predict Grotto geyser. Their results work quite well. Their 1997 linear regression formula for predicting the Interval Between Eruptions (IBE) was:

IBE = 190 + 1.7D

Where: IBE is in minutes and D is the duration in minutes.

Grotto Fountain Geyser: [Pictures] [Map]

Grotto Fountain is a beautiful cone-type geyser. Its durations are usually around 15 minutes but eruptions as long as an hour have been seen. Intervals are about the same as Grotto Geyser and range from about 6 hours to over a day. Grotto Fountain almost always starts a few minutes prior to an eruption of Grotto Geyser. The longer Grotto Geyser holds off before it starts to erupt, the taller Grotto Fountain Geyser becomes. Heights can range from 30-80 feet. The tallest eruptions of Grotto Fountain usually occur prior to the first Grotto eruption after a long mode eruption of Grotto.

Grotto Fountain is always fun to see. Not only is it a beautiful geyser but once it starts you are almost guaranteed to quickly see eruptions from South Grotto Fountain and Grotto Geysers. All of this activity in a relatively small area and within a relatively short period of time is a lot of fun.

What to look for:

Prior to an eruption of Grotto Fountain, three things in particular should be looked for. First, the Indicator Spring which lies in front of Grotto Fountain should be nearly full. This pool fills slowly prior to the eruption. Once water is easily visible from the trail, an eruption is getting near. At this point the pool rises and falls in 20 minute cycles. At the high point, it is about an inch below overflow, at the low point it is about 4 inches below overflow. These cycles correspond to the level of splashing seen in Grotto Fountain. When Grotto Fountain does finally starts, it does so when the pool is at its high level.

The second item to look for is heavy splashing from Grotto Fountain. The amount of Splashing from Grotto Fountain is on the same 20 minute cycle as the Indicator Spring. When the Indicator Pool is low, the splashing from Grotto Fountain is also low. When the Indicator Pool is high, the splashing from Grotto Fountain is high.

The third thing to look for, and possibly the most telling, is for a large pool of standing water to have formed around Grotto Fountain's vent. This standing water is caused by the heavy splashing from Grotto Fountain and is the best indicator of how heavy the splashing actually is.

The experienced observer uses these three observations to judge how close the next eruption is.

Grotto Fountain starts fairly slowly. the splashing from the vent slowly grows into near steady jetting. the steady jetting then begins to grow taller. Even at this point the eruption could be delayed, especially if Startling Geyser starts to erupt or if the "central vents", the vents located between Grotto Geyser and Rocket Geyser, start to erupt. These two cases can delay the start of Grotto Fountain by as much as an hour or more. The eruption of Grotto Fountain is usually guaranteed when the steady splashing reaches about four feet. At this point the character and sound of the activity changes from a fairly steady splashing to a steady jetting. The eruption then continues to grow.

Soon after Grotto Fountain starts, South Grotto Fountain usually starts to erupt. Also, the Indicator Pool starts to overflow. If you hadn't noticed it before, Grotto Geyser also usually starts to make gurgling sounds. Much of the time Grotto Fountain precedes Grotto by about 2-5 minutes. The longer it precedes Grotto by, the taller it gets. On very rare occasions, it has preceded Grotto by as much as 50 minutes.

Once Grotto Fountain starts, keep an eye on Grotto. The most spectacular part of Grotto's eruption is usually the start. Once Grotto starts, Grotto Fountain can continue to grow taller for a short period but after a minute or two it starts to shrink in size. Grotto Fountain's eruption is usually completed within 10 minutes of the start of Grotto. It is only at the very end of the eruption that Grotto Fountain lives up to its fountain name. At the very end of the eruption, the steady jetting changes to fountain-type bursting.

Indicator Spring: [Map]

During the few hours prior to an eruption of Grotto Geyser, Indicator Spring slowly rises until it is easily visible from the trail. It can then be seen that the water level fluctuates in twenty minute cycles. At the high point the water may be near overflow. At the low point it may drop four inches. The cycles correspond to those seen in Grotto Fountain Geyser. Because the water level in Indicator Spring is easy to see, it is often looked at as one of the indicators for an upcoming eruption of Grotto and Grotto Fountain. After Grotto Fountain's eruption, the water level in Indicator spring drops. Then Indicator Spring acts as a drain for a portion of Grotto Geyser's runoff.

Indicator Spring was seen to erupt once. This eruption reached about 6 feet.

South Grotto Fountain Geyser: [Pictures] [Map]

South Grotto Fountain Geyser is a fountain-type geyser. It usually only erupts toward the start of a Grotto Geyser eruption although it has been known to start just prior to an expected eruption of Grotto Fountain Geyser and delay the start of that geyser and as a result the start of Grotto Geyser.

Intervals for South Grotto Fountain are about the same as those for Grotto Geyser, 6 hours to over a day. Durations are around 30 minutes. Its maximum height is about 15 feet. It makes a pretty companion for Grotto Fountain Geyser.

What to look for:

Since South Grotto Fountain usually starts at about the same time as Grotto Fountain, see the description for that geyser for more information.

Spa Geyser: [Pictures] [Map]

Spa Geyser erupts almost exclusively during Grotto Geyser's long mode eruptions. Spa is a fountain-type geyser. Heights of the widely spaced bursts can range from anywhere between 3 feet and 45 feet. Bursts usually come about one to two minutes apart and can often surprise visitors that are not expecting them. Larger bursts are quite spectacular and make and interesting sound. Even small bursts are fun since it is possible to see into the pool and watch the large steam bubbles rise to the surface and ultimately cause a burst of water.

What to look for:

Spa Geyser will often start erupting about three hours or so into a long mode eruption of Grotto Geyser. Once Grotto Starts, Spa usually starts to slowly fill. Prior to the start of Spa's eruption, Spa starts to overflow. Often it will reach overflow, drop a few feet and then refill and overflow again before it starts to erupt. The eruption usually starts slowly with bursts being widely spaced and quite small. Eventually the size of the bursts can increase in size so that they are fairly spectacular. The activity can last for a few minutes to hours. Once the eruption is finished, the pool will drain down. If the Grotto Geyser eruption is particularly long, Spa can stop, drain down, refill and start again.

Startling Geyser: [Map]

"Startling" is an unofficial name of relatively recent use. the name came about because observers were startled one day when this small geyser, whose vent is partially hidden from the trail, started to erupt. Unfortunately, Startling almost always delays the start of the much bigger and more spectacular Grotto Fountain Geyser and Grotto Geyser. These delays are often as much as an hour. To make matters worse, once Startling starts, it sometimes has a series of eruptions on intervals of about 20 minutes, each of which further delays the start of the other geysers in the group.

All is not lost though. Fortunately, Startling is fairly rare. In fact, it is rare enough that observers are often intrigued by its unexpected eruptions.

Startling Geyser is a fountain-type geyser. Its duration is about four minutes and its height is about 10 feet. It looks like a small South Grotto Fountain Geyser which sometimes erupts with it.

What to look for:

Startling Geyser starts at about the time Grotto Fountain would be expected, see the description for that geyser for more information.

Rocket Geyser: [Pictures] [Map]

Rocket Geyser erupts with Grotto Geyser. Only on extremely rare occasions has Rocket been reported to erupt by itself. During most of Rocket's eruption, it is not very spectacular. The eruption consists of continual splashing to at most 10 feet. But on occasion, Rocket can take over the entire eruption from Grotto Geyser and turn into a truly spectacular geyser. These Major eruptions start quickly, raising in a six foot wide column of water up to 50 feet into the air. The column then shrinks down to 25-30 feet and holds for a while before continuing to shrink and both geysers returning to their splashing play. The total duration of the major eruption is usually just short of 10 minutes.

What to look for:

Rocket Major eruptions almost exclusively occur during Grotto Geyser's short mode eruptions. They usually come 1.5 to 2 hours into the eruption but sometimes can come earlier or later. Often Grotto finishes its eruption soon after a Rocket Major but not always. Rarely, Rocket can have two eruptions during a Grotto short mode eruption.

Other than the time window, there is not much to look for prior to a Rocket Major. A good sign is a dying down of the activity in Grotto Geyser and larger splashing from Rocket. Once a Rocket Major starts, it takes over the entire eruption from Grotto and Grotto falls completely silent. Towards the end of the major eruption, Grotto slowly starts to come back to life.

[ Geyser Hill Group - Map ] [ Old Faithful Area - Map ]
[ Castle Group - Map ] [ Sawmill Complex - Map ] [ Grand Group - Map ]
[ Riverside/Morning Glory Group - Map ] [ Old Road Group - Map ]

[ Biscuit Basin - Map ] [ Black Sand Basin - Map ]

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