[Geysers] Some thoughts on Giant

[Tara Cross]

Scott's comments about Giant a few days ago are certainly interesting and raise some questions.  The first question is, can a list of Giant eruptions be pieced together in the absence of the electronic data?  (I do not mean to ruffle any feathers, but last winter the electronics were updated several times; however, the last such update came in May of 2007 and I have heard nothing since.)

I have attached a list of Giant eruption reports based almost entirely on listserv posts.  It includes the author and date of relevant listserv posts, in case anyone wants to look them up in the archives.  One thing that became very clear as I compiled the list is that we would know precious little without reports from Carolyn Loren--so a big thank you to Carolyn for keeping track of Giant over the winter.

When I compared this list to Scott's, two things caught my attention:

1.  Scott's list includes a possible eruption on Dec 10 at 1630ie wc.  This was apparently a webcam observation, but I did not find a report or snap posted on the listserv.  Based solely on the reports to the listserv, though, it seems that the signs that had been replaced on Dec 7 were still there on Dec 13, which places some doubt on the Dec 10 eruption report.  If someone has more information on this, I am happy to hear it.

2.  Moving ahead to late March/early April, please note that I put an asterisk next to the notes for the March 28 and early April eruptions.  This is because of some confusion with one of Carolyn's posts.  The subject line says, "Signs, marker in place," but the text of the post says "April 4, replaced Giant signs and F&M marker."  This list assumes that the text is correct and the subject line was accidentally wrong.  If Carolyn is reading this, maybe she can shed some light.

A final item relates to Scott's hypothesis that no eruption occurred between April 16 and 29.  Initially, when I heard that the signs had been replaced when the trails opened on April 28, I thought that an eruption had occurred during the interim while the trails were closed.  However, I have not heard any reports that the signs were ever replaced after the April 16 eruption, so it is certainly possible that the signs had been washed by that eruption, and not by an eruption between April 16 and 29.  Again, if anyone has additional information, it would be much appreciated.


I won't attempt to interpret the behavior that has been observed recently, especially since I'm not there to see it myself.  Even though there isn't much information available about what Giant was doing in the winter, there is evidence of a couple of changes that occurred during the winter months, possibly in February.  I'm basing this on several things:

1.  The visitor who reported Giant's eruption on February 27 said that Mastiff erupted prior to Giant, even though it was not a marathon recovery eruption.  Carolyn Loren said that the report came from a French ski tour guide; there is no way to know if that person could have mistaken large surges for an actual eruption but it is quite possible that the 'bimodal phase'--in which Mastiff erupted only with marathon recovery Giant eruptions--had ended by that time.  The only eruptions seen prior to that (Dec 30 by Kitt Barger and Feb 19 by Graham Meech) had been marathon recovery eruptions (and Mastiff erupted prior to both).

2.  In this same vein, a detail in Steve Eide's report on the 4/29/08 Giant eruption which I do not remember seeing in prior reports is that he saw Mastiff erupting prior to Giant's start.  So even if Mastiff did not erupt prior to the Feb 27 eruption, the 'bimodal phase' had definitely ended by April 29.  (And, incidentally, the fact that Mastiff erupted probably also means that the eruption did *not* come from a Feather restart--without a report from someone who was actually there, I think that's too much of a stretch.)

3.  The April 29 eruption was also unusual because it occurred about 5 1/2 hours into a marathon.  While that window is not unheard of for Giant, it is definitely unusual--even taking behavior from the past 20 years into account.  Giant did not erupt more than 3 1/2 hours into a marathon at any point during 2005-07 (and probably going back a while before that, but I don't have the data handy).

4.  The electronics aren't available for Giant, but they are available for Grotto.  Scott mentioned that perhaps a good, long marathon could get Giant back on track.  The trouble is, based on the data available through April 8, Grotto isn't having those anymore.  Understanding that this tells us nothing about the past 5 weeks, I still find it noteworthy that no marathons exceeding 24.25 hours in duration occurred between Feb 14 and April 8, a stretch of nearly 2 months.

Based on these facts, the reports of weird/different behavior occurring during hot periods weren't surprising.  However, I share Scott's concern that the intervals have been getting longer, and we are perhaps seeing the end of the phase of short intervals.  Someone else will have to comment on the activity from the Purple Pools but I personally do not recall any time in the past 7 years that North and East Purple were overflowing, even when Giant was not erupting frequently.

I am also wishing for this to be just a slowdown, but it definitely doesn't sound good.  Thanks to Scott, Carolyn, and all those passing along reports to the listserv.

--Tara Cross
fanandmortar at hotmail.com

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