[Geysers] Activity at Grotto/Giant, Aug 27-30

[Tara Cross]

The following is a summary of the activity at Grotto and Giant prior to the August 30 eruption of Giant.  August 27-28 The Grotto marathon that had started at 1305 on Aug 27 ended at 1304 on Aug 28 for a duration of 23h59m.  Even though it was less than 4 days into the interval, a group of us waited into the night for the recovery hot period.... August 29 0107 Oblong0143 GHP, d~9 1/2m.  FS 15s, Mastiff boiled 1-5 feet, India 100%. Given the strength of the recovery hot period, we felt pretty safe leaving Giant for a few hours, during which several hot periods were doubtlessly missed.  The rest of the day progressed as follows: 0638 Grotto Fountain0655 Grotto, d=32m0853 GHP, d~5 1/2m.  FS active, Mastiff overflowed lightly.0957 GHP, d~2 1/2m.1019 Oblong1103 GHP, d=1m50s.  Feather, Rust, & SW Vents, Mastiff overflowed lightly.1157 Bathtub1246 GHP, d=6m48s.  FS 22s, Mastiff boiled 2 feet, Cave 4 inches. This hot period didn't strike me as all that strong, but it was interesting in that Bijou came on before Feather stopped.  All of Mastiff's boiling action took place early in the hot period, and then when Bijou came on it dropped below overflow while Feather continued to erupt.  I didn't manage to record the exact time for Bijou's start, but I was careful to watch for it in the hot periods that followed.  We had been looking for Grotto to start around 1100 based on the interval formula, but once again there was a sizeable delay of about 3 1/2 hours. 1407 GHP, d=2m46s.  FS 27s, Mastiff overflowed lightly, SW Vents started 10s before Feather.1416 Grotto Fountain1421 Grotto, d=32m1507 GHP, d=2m38s.  Feather & SW Vents only, Mastiff overflowed lightly.1509 Oblong1603 GHP, d=4m.  Feather & SW Vents only, Mastiff overflowed lightly, SW Vents started before Feather.1659 GHP, d=2m.  Feather & SW Vents only, Mastiff did not overflow, SW Vents started 50s before Feather.1758 GHP, d=1m15s.  Feather & SW Vents only, Mastiff did not overflow, SW Vents started 40s before Feather, Unnamed vent between Bijou & Catfish active at end of hot period.1821 Grotto Fountain, d=15m1825 Grotto, d=50m1858 GHP, d=7m02s.  FS 87s, SW Vents started 20s before Feather, Cave 4-6 inches. There was a lot going on during this hot period.  During the first 3 minutes Mastiff was flat or boiling lightly, mostly to 1 foot or less but there were occasional spikes to 2 feet.  Then Mastiff went calm, and Bijou came on about 4 minutes into the hot period, accompanied by splashing from the unnamed vent between Bijou & Catfish.  At that point Mastiff dropped slightly below overflow and Cave began boiling vigorously to 4-6 inches.  This activity persisted for over 2 minutes, with Mastiff hovering just below overflow and Bijou on, until finally Mastiff dropped out of sight and Feather quit.  Feather was off for 2m13s and then came back on, without Feather Satellite, for a restart lasting 4m48s.  There was some surging in Giant's cone, but most of it was angled and I was never impressed.
 I was, however, pretty convinced that nothing of significance was going to occur at Giant for a few hours, so I opted to get some dinner and prepare to spend the night at Giant, planning to return in time for the next Grotto which was due to occur around 2300.  While I was away, Oblong was called at 1946.  Then: 2307ie Grotto Fountain2309 Grotto, d~50m2317 Bathtub August 30 0007 GHP, d=2m04s.  Feather & SW Vents only, Mastiff overflowed lightly, SW Vents started 30s before Feather.0015 Oblong0118 GHP, d=4m48s.  Feather & SW Vents only, Mastiff light boiling with moderate overflow, SW Vents started 20s before Feather.0219 GHP, d=1m20s.  Feather & SW Vents only, Mastiff did not overflow.0317 GHP, d~2m.  Feather & SW Vents only, SW Vents started before Feather.0419 GHP, d=6m.  FS 45s, Cave 4 inches, India 50%, SW Vents started 30s before Feather. I checked on Grotto when it was due at 0340 and found that South Grotto Fountain was active, having small eruptions every few minutes.  Then I returned to Giant for the 0419 hot period, which turned out to be a third strong hot period in which Bijou turned on early.  This time I couldn't actually see what Mastiff was doing due to steam on the platform, but once again all of its runoff was produced in the first several minutes of the hot period prior to Bijou coming on at about the 4-minute mark.  Two minutes later, Feather quit.  There was a restart, but it was short and weak. Since I had been out by myself for most of the night and it was clear that this was as close as Giant was going to get to having a strong hot period, I decided to head in for a nap and a meal, even though Grotto was still due.  I was relieved to see Mike Lang in the parking lot and passed along the night's information to him.  He called the rest of the day's events, which occurred as follows: 0458ns Grotto, d~1h20m0514 GHP, d~2m.  Feather & SW Vents only.0521 Oblong0547 Rocket major0614 Bathtub0709 GHP, d=3m03s.  Feather & SW Vents only, Mastiff did not overflow.0807 GHP, d=1m03s.  Feather & SW Vents only, Mastiff did not overflow.0905 Bathtub, SW Vents on strong and Feather overflowed, but no hot period.0957 Oblong After the string of very weak hot periods and bathtubs, I and many others figured there was a good chance for a strong hot period with the start of the next Grotto.  I arrived at Giant in time for Oblong, then moved to the cage.
 
By this time, I had determined that Giant had a good chance of erupting on the first hot period where Bijou came on and Mastiff managed to continue overflowing and boiling.  There was also a clear difference between weak hot periods and strong, in that Feather Satellite had not been active with any of the weaker ones for over 18 hours.  So, I watched the hot period with great interest.
 
Bijou paused, and water rose in Mastiff.  The SW Vents started about 40 seconds prior to Feather, which started at 1008.  Within a minute we knew this would be the strong hot period, as Feather Satellite had joined in.  Mastiff boiled to 1-2 feet in the first 3 minutes, and then things started to progress quickly.  3m37s into the hot period, Bijou had its first splash and built into full eruption, joined 25 seconds later by the unnamed vent between Bijou & Catfish.  Cave's activity increased from vigorous boiling to full eruption to 3 feet just under 5 minutes into the hot period, and Mastiff surged 4-5 feet with heavy overflow.
 
Approximately 7 minutes into the hot period, Mastiff went flat and then dropped.  Cave's activity quickly subsided, and Feather and Feather Satellite weakened enough that I thought they might stop, but they persisted and Giant began vertical surging to 1/4 the height of the cone.  Bijou went into steam, and the surging rapidly built to 3/4 the height of the cone.  Then there were several surges to the top of the cone before the eruption commenced, 9m36s after the start of the hot period, at 1017.38.
 
I chose to view the eruption from the main boardwalk towards the GIP so that I could see Giant's column backlit by the morning sun; I heard that others had a lovely view as well from further down towards Oblong.  Giant burst up to 30, then 50, then over 100 feet, and then an enormous surge threw water to what I guessed to be well over 200 feet.  The water cascaded back down in a glowing, sparkly curtain, and the word that immediately came to mind was, "Magnificent."  I was also impressed with how Giant maintained its height well into the eruption.
 
Grotto Fountain started at 1049, with Grotto following at 1050.  It was a marathon, though I do not know the duration.  The duration of Giant was 104 minutes.
 
--Tara Cross
fanandmortar at hotmail.com
 
 
 
 
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