I'm not sure about this, but I think I remember a couple of cases in 1997 when Giant erupted either during a marathon recovery or during the first Grotto after a marathon, and that Grotto turned into a second marathon.  I also think I recall that consecutive marathons were otherwise very uncommon in '97.    Even so, it's a huge leap--almost meaningless, really--to try to deduce cause and effect from these observations.  Do Giant eruptions cause marathons?  Do marathons starting cause Giant to erupt?  Or is there some invisible third system state variable that causes both events to be associated with each other?  I have difficulty imagining surface phenomena that would allow us to favor any of those conclusions over the others, given our limited knowledge of how the system actually works.  The best we can do is conclude that there is (during some years) an association between Giant eruptions and Grotto eruptions that later turn out to be marathons.    We tend to think of the sequence as Giant causing the marathon because that's usually the order in which we conclude an event has happened--First we see Giant, then a few hours later we decide that Grotto has been erupting long enough to call it a marathon.  That doesn't mean it's the order in which the events were determined.  Maybe the system knows long before Grotto starts whether it's going to be a marathon (or at least going to have a high probability of being a marathon).  Maybe Giant erupting affects that probability.  Maybe it doesn't.  There's just too much hidden to be sure. David Schwarz <div>On 6/7/07, Tara Cross <<a href="mailto:fanandmortar@hotmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> fanandmortar@hotmail.com</a>> wrote:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div> >The Group 3 Giant eruptions can be viewed as part of Group 1 but are those Giants that started while >Grotto was erupting and forced Grotto to marathon causing this subset to be displaced to longer times.   An open question to Tom or anyone else:  Is there statistical or observational evidence that Giant actually *forces* Grotto to marathon?   I've had this chicken-or-egg discussion with people a number of times, and I keep coming back to two things that make me uncomfortable with assuming that Giant will force Grotto into a marathon.   1.  Sometimes Giant erupts during Grotto, and then Grotto quits during Giant.  I know it's not terribly common, but it does happen, for example twice recently, on May 14 and May 24, as well as other times in the past.   2.  I mentioned the 3 cases in 2004 when Giant erupted 2-3 hours into a Grotto eruption that turned out to be a marathon.  Did we know for sure it was going into marathon before Giant erupted?  No.  But a marathon was very much overdue each time.  On August 2, there had been 7 normal Grottos since the last marathon, and on October 11, 6 normal Grottos.  In other words, we were very much looking for Grotto to have a marathon both of those times (and also on July 15, though I wasn't there to see it myself).   Is there something statistically that distinguishes between the Giant eruptions Tom mentions that "forced" Grotto into marathons, and the Giant eruptions that occurred while a *normal* Grotto was in progress?   Thanks!   --Tara Cross <a href="mailto:fanandmortar@hotmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">fanandmortar@hotmail.com</a> <hr>Change is good. See what's different about Windows Live Hotmail. <a href="http://www.windowslive-hotmail.com/learnmore/default.html?locale=en-us&ocid=RMT_TAGLM_HMWL_reten_changegood_0607" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">Check it out!</a> </div> _______________________________________________ Geysers mailing list <a href="mailto:Geysers@wwc.edu" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">Geysers@wwc.edu</a> <a href="https://mailman.wwc.edu/mailman/listinfo/geysers" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)"> https://mailman.wwc.edu/mailman/listinfo/geysers</a> </blockquote></div>