[Geysers] Grotto/Giant details, July 21-24

[Tara Cross]

The following is a summary of activity in the Grotto/Giant area prior to the July 24 eruption of Giant.
 
July 21
 
0717 Giant hot period, d=5m40s.  Mastiff surged to 4 feet, Feather Satellite active.
1033 Grotto Fountain, d=48m.
1103 Grotto
1318ie Giant hot period, d~2m.
1616ie Grotto Fountain
~1625 Grotto - marathon
 
The 0717 hot period was a marathon recovery hot period with impressive surging from Mastiff.  The Giant area was not watched closely for the rest of the day due to how early it was in Giant's window.  The Grotto marathon that started around 1625 ended at some unknown time overnight.
 
July 22
 
0816 Giant hot period, d=3m06s.  Mastiff flat, Satellite active.
1014 Bathtub
1053 Giant hot period, d=6m10s.  Mastiff surged to 4 feet, Satellite active, India 70% covered.
~1210 Giant hot period, d=unknown (saw aftermath)
1311 Grotto Fountain, d=31m.
1321 Giant hot period, d=4m45s.  Mastiff light overflow, Satellite active.
1327 Grotto - marathon, d~14h
1447 Giant hot period, d=2m20s.  SW Vents started 15s before Feather, no Satellite.
1522ie Giant hot period, d>2m.
 
Giant was under more careful observation on the 22nd.  Once again, the 0816 hot period was the recovery hot period, however this time it was very weak.  The next hot period at 1053 was considerably stronger.
 
July 23
 
0831 Giant hot period, d=9m10s.  Mastiff surged to 3 feet, Satellite active, India 100% covered.
1157ie Giant hot period, d>4m.  Mastiff surged to 1 foot, Satellite active.
1336 Giant hot period, d=3m44s.  Mastiff light overflow, Satellite active.
1442 Giant hot period, d=6m10s.  Mastiff surged to 2 feet, Satellite active, India 70% covered.
1548 Giant hot period, d=3m03s.  Mastiff surged to 1 foot, Satellite active.
1616 Grotto Fountain, d=19m.
1632 Grotto, d~20m.
1634 Rocket major, d~3m.
1656 Giant hot period, d=2m12s.  Mastiff light overflow, no Satellite.
1800 Giant hot period, d=6m.  Mastiff light overflow, SW Vents started 30s before Feather, Cave 3 inches.
1855 Giant hot period, d=1m35s.  SW Vents started 20s before Feather, no Satellite.
1954 Giant hot period, d=1m11s.  No Mastiff overflow, SW Vents started 40s before Feather, no Satellite.
2046 Giant hot period, d=4m56s.  Mastiff surged to 1 foot briefly, Satellite started 1m15s after Feather.
2149 Giant hot period, d=2m17s.  No Mastiff overflow, no Satellite.
2249 Giant hot period, d=2m23s.  Mastiff light overflow, no Satellite.
 
I will pause here because there were several significant things that occurred in the Grotto area during the string of weak hot periods in the afternoon and evening.  The first, and most obvious, was the Grotto start at 1632.  After the start of Grotto, we noted large surges in Rocket.  Some gazers were cheering for Rocket to start, and indeed it did, about 2 minutes after Grotto at 1634.  At first I thought Grotto might actually stop completely, because it died down and very little water was seen during Rocket's eruption.  However, it resumed its eruption as soon as Rocket finished.  Even then, though, the eruption lasted only 20 minutes or so, as it was off by 1652.
 
Given the short duration of Grotto, I was expecting the next eruption to occur around 2000-2030.  This was confirmed when Jan Johns came down to Grotto (for those who aren't aware, Jan and Lew Johns calculated a still-accurate duration-interval formula for Grotto in the mid-90s--for more info see the GOSA website's page on Grotto).  We were both intrigued to see that Grotto really did not look imminent; in fact, the boiling in Grotto Fountain died down.  I commented to Jan that when Grotto is "supposed" to erupt and doesn't, it has often meant that something is up over at Giant.
 
As the evening progressed, I noted that South Grotto Fountain was starting to have intermittent splashing to about 1 foot.  This eventually built into full eruptions sometime around 2200.  After the 2249 hot period I decided to keep an eye on the Grotto area.  Spa was full, overflowing, and pulsating.  As I watched South Grotto Fountain's eruptions, which lasted about 2 1/2 minutes and occurred every 7-16 minutes, I started to get a sense of deja vu.  Similar events had occurred prior to Giant several times in 2006, most notably on July 3, when South Grotto Fountain erupted in like fashion for at least 8 1/2 hours while Grotto followed a 10-minute eruption with a 12-hour interval.
 
As for Giant, I had been expecting a strong hot period with the Grotto start that was supposed to occur at 2030, which would have also been 12 hours after the morning's recovery hot period.  Yet all of the hot periods after 1800 had been weak.  There had been a gradual shift of energy to the South side of Giant's platform, with the Southwest Vents consistently starting prior to Feather and very little out of Mastiff.  And, as has become commonplace with such energy shifts, there was powerful depth charging in Mastiff between hot periods accompanied by steamy, strong eruptions from Bijou.
 
So as I sat watching South Grotto Fountain, it began to dawn on me that all of the day's events were in fact setting up a very strong hot period, and possibly even a Giant eruption.  When Paul called water rising in Mastiff, I rushed to tell the others in the cage (Paul and Suzanne Strasser, Andrew Bunning, and Adam Johns) what I'd been thinking about.  But I never had the chance....
 
The hot period started at 2356, with Feather again preceded by the Southwest Vents.  The hot period got off to a slow start, with Mastiff just barely overflowing and Feather Satellite waiting a full minute to come on.  Then, about 3 minutes after Feather, Mastiff picked up significantly, surging 3-5 feet and overflowing heavily--so heavily, in fact, that it was mostly obscured in steam for the rest of the hot period.  We also noted that Cave's bubbling continued to get stronger.  We all looked at each other--finally, we were getting the strong hot period.  The next few minutes were rather chaotic as we hurriedly tried to get into rain gear and cover our packs, just in case.
 
Approximately 5 1/2 minutes into the hot period, Suzanne called out that Cave was in full eruption to 3-4 feet, and at that same time I noticed an unexpected sound--a booming, jet engine roar from Bijou, which had turned on full force.  At that moment, I realized that this wasn't just a strong hot period, it was THE hot period.
 
We still couldn't see what Mastiff was doing, but India was covered by that time, and Cave continued to erupt.  About 8 minutes into the hot period, we knew that Mastiff had dropped because Feather and Feather Satellite noticeably weakened.  But they came back strong, and there were immediately strong vertical surges in Giant.  We all retreated to the main boardwalk as the surges got bigger and bigger and water poured out in front of the cone.  Giant didn't mess around this time--after two cone-filling surges, it commenced the eruption without further ado, sending a rocket of water to 30 feet at 0006.  This was followed by a series of bursts, each getting progressively taller and wider as Giant reached for the stars.  The golden water sparkled against the dark sky with elegant, breath-taking beauty.  I was too close to have a good height estimate but it was certainly not short--probably 200 feet or more.
 
The initial surge inundated the cage--and Paul's pack, which he had tried to save by moving it towards the GIP on the main boardwalk.  As we enjoyed having 4 maglites to illuminate the column, we heard screams approaching as Linda Strasser and her cousin Bill made their way to Giant, having watched the start from Castle.  We were later joined by Kevin Strasser and Stacey Glasser, and the 9 of us appreciated the fact that it wasn't terribly cold; in fact, I was overdressed, given that I had expected to spend most of the night at Giant.  The moon hadn't yet set when Giant started, but it was behind clouds so it didn't provide any light.
 
The eruption lasted 98 minutes.  Grotto was still quiet when we left the area shortly before 0200.
 
--Tara Cross
fanandmortar at hotmail.com
 
 
 
 
 
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