How to watch for Giant Geyser

by | Oct 1, 2015 | Geyser Watch

With the recent eruption of Giant Geyser, the excitement by the gazer community has delightfully increased.

This second tallest geyser in the world pulls a tremendous amount of water from the underground system that connects to other geysers, making it a complicated one to watch. So here’s my best attempt at making this as simple as possible, yet accurate – something to learn more if you’re new or simply visiting when Giant Geyser is active. I’ve been lucky enough to watch hot periods in the past and see one eruption in person (after literally running from the Old Faithful Inn dining room to Giant).


It’s apparent that Giant Geyser has had active phases and some long, very quiet phases over the years.

  • 1950-1955 it had remarkable activity.
  • 1956-1985 only 4 eruptions occurred.
  • 1986-1995 one eruption a year was seen.
  • Sept 1996-March 1998 again showed remarkable activity. This time the eruptions started with erratic intervals between eruptions of 6 to 33 days, but then settled down to a regular 3 to 6 day routine.
  • April 1998 to July 2005 the eruptions became more erratic from days apart to months apart.
  • Aug 2005 to 2008 more remarkable activity was seen.
  • 2009 to 2014 one eruption recorded in 2010.
  • 2015 – one eruption (so far)…

 So, as you can tell, right now we’re all waiting to see if this was another once a year event (very likely) or if it might possibly turn into another active phase. And, unfortunately, this is the time of year when there are few knowledgeable gazers around to help others learn what to watch for. In order to take good observation notes, it’s helpful to know what you might see.


Giant Geyser eruptions put out a tremendous amount of water, and during the times of remarkable activity, geyser gazers have noted connections between Giant Geyser and other geysers in the surrounding area.

As seems logical, the geysers on the Giant Platform are all connected, but so are the thermal features from Oblong Geyser down to include Grotto and Rocket Geysers as well as Spa Geyser, Marathon Pool and the Purple Pools (across the river and behind and ‘right’ of Giant). During the 1996-1998 activity, a correlation between Giant and Splendid Geyser (in the Daisy Geyser Group) was theorized, and perhaps research was conducted, but I am still looking for more information on that.

This theory did not appear to hold true during the 2005-2008 activity; at least one article mentions no research was done. But that doesn’t mean a connection didn’t exist – it just means it wasn’t seen so clearly. Thermal areas shift and change and are complex by their very nature.


Rocket Geyser (left) and Grotto Geyser (right)


Catching a start or end(ish) time for Grotto is helpful. The actual ‘start’ time for Grotto is taken when the first large splash comes out of the ‘back’ side of Grotto’s unique formation. Grotto doesn’t really stop suddenly, instead the energy slowly dwindles until only steam is seen.

Grotto also can have extremely long eruptions as well – known as “marathons” – which drain the system of quite a bit of water. This may lift enough water out of the system to help Giant Geyser out. If you’ve ever hauled a five gallon container of water, you know the weight of water (a pint of water weighs a pound).

Giant Geyser often likes to erupt on the first Hot Period after the end of a marathon eruption, but if it doesn’t erupt then, the only thing to do is try to catch as many Hot Periods as you can.

Bijou Geyser erupting on the Giant Platform. Catfish Geyser is not in just below Bijou.


Long eruptions of Grotto can slow and stop Bijou Geyser. So if you don’t know what’s happening with Grotto, if Bijou is off (and stays off), that’s not a bad sign for Giant.

If you see Bijou shut off – make a note of that time. It might be worth checking on it again in a few hours to see if it stays off (5-8). Then it might be worth the wait for a Hot Period.

Basically, the longer Bijou is off, the better. Short pauses of Bijou can and do happen, and are usually not worth the wait for it to stop again.

The GIP - Giant Indicator Pool

WATCH FOR: GIP (Giant’s Indicator Pool)

It might be more accurate to call this hole in the ground MIP because the water level in GIP closely matches the water level in Mastiff, but that is a help in watching for Giant Geyser because good water levels mean there’s enough thermal energy to be at least hopeful.

The water levels might also match in Giant, but checking that isn’t possible since the boardwalk (where it’s safe) doesn’t allow for that. You’ll find the GIP near the boardwalk between the Giant Geyser Platform and Grotto Geyser. There’s also Variable Spring in there, but more on that later.

Much of the time GIP sits empty as in the photo above, but if you see water, that’s a nice thing to jot down in your notes.

Water rising in Mastiff Geyser's front crater.


Water rising in Mastiff can result in a shut off in Bijou Geyser, and can signal an upcoming hot period. There’s much more to say about Mastiff, but that will wait for another article.

Mastiff is named for the breed of dog – that lies at the foot of Giant (to the ‘left’ as you look at this group). If you are lucky enough to witness an eruption of Giant, you will also get to see Mastiff if the energy to start an eruption comes from that side.

Make a note if Mastiff starts first or Giant (sort of how gazers track whether Grand starts first or Turban) because that tells a bit of information on where the energy for this eruption came from (North or South) – that is, if eruptions behave similarly to how they did in 2005-2008.

Oh, and Mastiff has erupted on its own before – without Giant joining in. That’s incredibly rare and has only happened a couple of times that I’m aware of.

Mastiff (back left), Feather's Satellite and Feather Vent, Emerald Vent ? (front center), Rust Vent ? (mid center), Giant Geyser (back center)


Hot Periods are an opportunity for Giant Geyser to erupt, and you won’t see an eruption of Giant without starting with a Hot Period first. On the large sinter platform there are many smaller vents between Giant’s large geyser cone and the viewing platform. When the water levels are good, some of them will start to erupt.

The main one to watch is “Feather Vent”. It’s called “Feather” because the eruption looks – well – much like a feather. It’s also been called “Christmas Tree” in the past.

The start of “Feather” is the start of the hot period for Giant Geyser. But if you walk up, still note the time, but put i.e. after it to indicate it was already In Eruption at that time. And note the time “Feather” stops (end of the Hot Period) if Giant doesn’t erupt on that hot period. “Feather” can restart as well, so just take notes on what you see.

Giant Geyser Sign rolled during an eruption of Giant Geyser


If Giant Geyser erupts, you’ll likely see surging from Mastiff, and vertical columns of water also surging in Giant’s cone. This vertical surging is different from the ‘left to right’ splashes from another vent in Giant’s cone that isn’t a part of an eruption of Giant. Eventually the vertical column will lift and the eruption is on.

It’s exciting to witness up close, but with this large geyser, some of the best photos come from standing back on the boardwalk (or even clear over on the paved path). Eruptions can last an hour or so – with the tallest water bursts coming at the start and slowly lowering in height and increasing in steam as the eruption progresses.


This is easy to tell because the sign marking Giant on this large sinter platform has been tumbled around by the water phase of Giant Geyser.

Giant Geyser hot period 12 June 2007

While there are many other nuances to learn about the behavior with Giant Geyser and all of its neighbors, this hopefully gives at least a very basic overview. I will work to write more articles on this (especially if we see more hot periods) – and  knowledgeable gazers are cordially invited to write up something here as well if they wish – and by all means, correct me if I’ve got something wrong. Many thanks to all who have contributed information on Giant Geyser in the past (in many volumes of the Geyser Gazer Sput and in online discussions), and especially to Tara Cross for compiling extensive information on the 2005-2008 activity in GOSA Transactions Volume 10.

And to help you remember this information (whether it’s needed next week or in five years), Jake Young of Geyser Times has created a PDF file of a Flow Chart of what to expect you can download.

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