[Geysers] Geyser Report 6/21/2016 (Stephens)

[Lynn Stephens]

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Thanks to Will Boekel for a report of Pink Cone ie at 2313ie on 6/20, confirming "middle of the night" eruptions following the jump shift caused by the aborted eruption on 6/18/2016. I took the time this morning to get a Twig duration--29 minutes.  I hoped to get another duration this afternoon but Twig didn't erupt with the late afternoon eruption of Fountain.  I came in early today.  As of 1715 the road bubblers had not started any activity. Overnight I was thrown a second curveball on smaller geysers that I watch.  In editions of Geysers of Yellowstone prior to the current edition, T.S. Bryan included statements to the effect that although intervals range from 5 to 10 hours, most intervals were 9-10 hours, and Till is highly regular at 9 hours (substitute "current" interval for various editions).  In the most recent edition Bryan dropped any reference to the 5 hour interval.  Prior to today I had only seen one instance where Till did a "jump shift" indicating it had thrown in a super short interval of 5-6 hours.  Well, it did it again overnight.   Recent major to major intervals had been 10h54m, 10h20m, and 10h15m.  I caught both majors yesterday, one at 0549 and one at 1609.  I didn't bother getting up for this morning's eruption.  I was watching Flood this morning when I suddenly saw a steam cloud rise from Till 0850ns.  I rushed over to confirm that Till was having a major eruption--a presumed double interval of 16h41m which probably consisted of a super short interval of about 6 hours and a normal interval of about 10 3/4 hours.  The eruption ended at 0922 for a normal duration.  The first afterburst occurred when expected and lasted just under 8 minutes, which is the common duration this season for the first afterburst.
 
I recently heard someone say that it seemed as though Grand Geyser is bimodal, with either "short" or "long" intervals.  I examined the data from geysertimes for the last 100 intervals ending with the 6/20/2016 1840 eruption of Grand.  Four of the "intervals" in geysertimes were double intervals, so I had 96 intervals to work with.
 
First, the descriptive statistics for closed intervals, with statistics from 2011 for comparison purposes:
 
                                  Closed intervals                Geysertimes        Ralph Taylor 
                                              2016                          2016                   last month ended 8/17/2011
 
count                                 96                                   100                             82
minimum                         6:10                                 6:10                           6:04
mean                                7:36                                 7:52                           9:08
median                             7:07                                7:09                            9:16
maximum                       11:00                             15:54                          12:46  
standard deviation        1:06:47
coefficient of 
         variation                 14.64%                                                            15.29%
 
Because only 4 double intervals are included in the geysertimes calculation, the 2016 median for closed intervals is only 2 minutes less than the median calculated by geysertimes.  But the mean interval is 16 minutes less when the four double intervals are excluded.  To people complaining about the "long" Grand intervals, the median was over two hours linger in 2011 than it has "recently" been in 2016.
 
With respect to the distribution of 2016 closed intervals, the distribution is not bimodal.  Rather, it is skewed, with a long right hand tail to the distribution.  The Fischer-Pearson coefficient of skewness has a value of zero for a normal distribution, and any distribution that is symmetrical should also have a value near zero.  The Fischer-Pearson coefficient of skewness for the 96 closed 2016 intervals is .99, indicating the distribution is skewed toward the right.  
 
Intervals grouped into 15 minute categories showed the following distribution:
 
                            Number         Percent           Cumulative Percent
6:00-6:15               3                         3%                        3%
6:16-6:30               7                         7%                     10%
6:31-6:45             13                      13%                      23% 
6:46-7:00             19                      19%                      42%
7:01-7:15             12                      12%                      56%
7:16-7:30               2                        2%                       58%
7:31-7:45               5                        5%                       65%
7:46-8:00               7                        7%                       71%
8:01-8:15               3                        3%                       74%
8:16-8:30               2                        2%                       76%
8:31-8:45               6                        6%                       82%
8:46-9:00               3                        3%                       85%
9:01-9:15               2                        2%                        88%
9:16-9:30               0                                                     87%
9:31-9:45               4                        4%                        92%
9:46-10:00             2                        2%                        96%
10:01-10:15           2                       2%                         98%   
10:16-10:30           0                                                     98%
10:31-10:45           0                                                     98%
10:46-11:00           1                                                    100%
 
Using a prediction window of 7 1/2 hours +/- 90 minutes, 56% of the eruptions were captured in the first 75 minutes of the window.  In fact, nearly half, 46%, of the intervals were catured between 6h31m and 7h15m.   If you skipped the first half hour of the window there was only a 10% chance of missing the eruption.
 
But once the window reached 7h15m, the distribution flattens out.  The remaining 44% of the intervals are spread across a 3 hour 15 minute spread. There currently is no window that works better than the current window. Nongeyser notes:  The other day I stopped a man walking toward Castle carrying fishing equipment.  When I told him the Firehole River is closed through the Upper Geyser Basin, he acted very surprised because he said when he asked the ranger for the best place to go fishing, the ranger told him the "Firehole."  I suggested he get a copy of the fishing regulations so he could see which sections of the Firehole are closed.   This afternoon I was sitting beside the bike trail from Biscuit Basin to Splendid/Daisy when two fisherman walked past me.  When I commented that the river was closed upstream from the bridge, one of them said, "They didn't catch me two years ago."  Maybe I should start carrying copies of the fishing regulations again so I can hand them out to people. Semi-geyser related:  I though the photographs of Clepsydra mislabelled as Spasm were probably attributable to the placement of the signs at Fountain Complex.  Some of the photographs even include a picture of the Spasm sign with Clepsydra erupting in the background.  When the boardwalk was moved recently the Spasm sign was placed on a lower board rather than the top board, but since it is the first sign people see and Spasm isn't obvious, people still call Clepsydra Spasm.  Today when I corrected someone, they pulled out a copy of a Yellowstone guidebook and showed me the section about Spasm.  Although they had an earlier version of the guidebook, the "Updated Fourth Edition" still contains the language "Spasm has a yellow-stained cone and pale green water."  No wonder people are confused!  
 
Lynn Stephens  

 		 	   		  
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