[Geysers] Fan & Mortar Report from Tara Cross

[Pat Snyder]

Tara is having trouble posting, so I am forwarding this report on Fan  
& Mortar.
Pat Snyder

This report covers Fan & Mortar's activity while I was in the park,  
June 24-July 3.

Fan & Mortar's eruptions since April:

June 24 @ 0646ie (interval ~2 1/2 months)
June 28 @ 0714 (I~4d00h28m)
July 2 @ 1433 (I=4d07h19m)


My arrival in the park did indeed get Fan & Mortar going again; it was  
seen in eruption on June 24 by a group of gazers who were at Grand.   
Dean Lohrenz later told me that he wasn't surprised to hear about an  
eruption because he had seen better water levels in the days prior to  
the eruption.  He said he never saw any actual event cycles (splashing  
in Main Vent, Bottom Vent eruptions, etc), but he did see High and  
Gold maintain high water levels for over 10 minutes, to the point that  
he thought they might go into lock.  His description sounded similar  
to reports of minor activity before Fan & Mortar ended their 43-day  
spring mini-dormancy in 2003.

People asked me when I thought Fan & Mortar could erupt again, and I  
said my guess was 1-2 weeks, but it could be as short as 3 days.  I  
will admit that I was a little surprised that the interval was only 4  
days, but pleasantly so, even though they chose the one morning on my  
entire trip when I decided to sleep in a little bit.  The start was  
seen by Hans Kaufman, who reported that the eruption started from a  
classic lock.  As far as I know, no other details are known.

After such a short interval, people were keeping an eye on Fan &  
Mortar on day 3.  David Schwarz called a River pause with Main Vent  
splashing on July 1.  I forgot to ask David how long the River pause  
lasted, but after the pause events took place as follows:

1253 River on
1303 last Main Vent splash, Bottom Vent's runoff made it almost to the  
River
1306 Gold on
1310 Angle on
1325 High vent in lock, Gold steady, and Angle splashing
1329 Upper Mortar surging began
~1333 Main Vent splashed
~1335 High vent out of lock
1339 last decent water in Upper Mortar
1341 River off

Frying Pan was also on but I forgot to write down the time.  I was not  
very optimistic in the first 10-15 minutes after Gold came on because  
the water levels kept dropping and then coming back.  When Gold and  
High dropped, water was not visible in either vent for several  
seconds.  I had actually written off the cycle, until I heard rumbling  
in Mortar and High suddenly started to build towards lock.  Though  
High was erupting steadily, fluctuating between 6-10 feet, I was never  
totally convinced that Gold wanted to join in the lock, and Angle  
never joined at all, going back and forth between splashing and  
steam.  The Upper Mortar surges started about 1-2 minutes apart, but  
at their peak they were coming about 30 seconds apart.  None of them  
lasted more than about 5-8 seconds, but several completely filled the  
cone, and enough water spilled over the sides to fill all the basins  
on the back of its cone.  For the first 5 minutes or so, Upper  
Mortar's surges did not have much visible effect on the strength of  
High and Gold, but then they began to weaken somewhat, and for several  
minutes they were going up and down before they finally dropped for  
good.  Main Vent evidently had one splash though I did not see it  
myself; I was intently looking for something from East Vent, but all I  
ever saw were a few steam puffs.

There were two things I found particularly notable about this event  
cycle.  First, the entire cycle was rather elongated; it took 13  
minutes for Gold to come on, 19 minutes after that for High to go into  
lock, the first Upper Mortar surge was 36 minutes after the start of  
River, and River was on for 48 minutes total after the pause.  In my  
experience this is an indication of "spring mode" behavior; similar  
timing was seen prior to spring eruptions in 2002 and 2003.  Secondly,  
I can unequivocally state that this is the most I have ever seen F&M  
do without actually erupting.  I have seen a lock with splashes from  
Main Vent and no eruption, and I have seen good Upper Mortar surging  
with no eruption, but never a combination of the two.  It should be  
noted, though, that when eruptions were triggered by Upper Mortar  
surging in 2001-2004, the first water was almost always seen in Upper  
Mortar within 12-13 minutes after the start of River--in other words,  
Upper Mortar needed to have water early in order to trigger an eruption.

David Schwarz stayed at Fan & Mortar after the cycle had ended and  
reported that after a period of quiet, River came on, and then stayed  
on weakly for over 30 minutes without action from the other vents.  He  
said it looked like Fan & Mortar thought they had erupted and were in  
a weak recovery phase of some sort.  Based on my previous experience  
with false locks, I thought it would be at least 24 hours before F&M  
had another chance to erupt (it has come back sooner than that one  
time that I remember, but that was during a phase of consistently  
short intervals).

So, I wasn't actually feeling terribly optimistic when Main Vent  
started splashing on the afternoon of July 2nd...  Events occurred as  
follows:

1330 River on, Angle had been splashing occasionally and had several  
splashes during River
1333 Gold on
1340 River off (I don't know if this was just a weak cycle or a Gold  
pause; Angle had a couple of weak splashes but it didn't really have  
definite start)
1343 Main Vent splash, splashing became consistent and continued for  
about 20 minutes; Bottom Vent also splashed enough to trickle runoff  
to the river
1354 River on
1413 Gold on
1419 Angle on
1422 High and Gold steady
1427 High vent in lock, Gold steady to 3-5 feet, Angle splashing
1432 Upper Mortar huge surge, 5-8 feet over the top of the cone, much  
stronger than the previous day
1433.05 East Vent start, followed immediately by the rest of the vents

Once again, the cycle was elongated; it took 19 minutes for Gold to  
come on and 33 minutes for High to go into lock.  However, there were  
some important changes from the previous day's events.  Most notably,  
the water levels were a lot more consistent once Gold came on; Gold  
did go into steam for a few seconds once, but the water levels  
immediately came back and never dropped after that.  Once again, Gold  
was steady but only to maybe 5 feet.  Angle had water at first, went  
into steam phase for about a minute, then came back again.  Upper  
Mortar's surge looked a lot like the surges that triggered Upper  
Mortar initiated eruptions in 2001-2004, and it was only about 10-15  
seconds between the end of the surge and the start of the eruption.

Something that started happening in 2004 and 2005 and continued with  
the eruptions I saw in 2007 was that after having its initial surge,  
Mortar would stop erupting and then not start again for 2-4 minutes,  
so that Fan was erupting by itself during the first few minutes of the  
eruption.  I watched for that this time, but Mortar's behavior was  
more like what it had been prior to 2004; I never saw Upper Mortar  
pause, and Lower Mortar had its usual pause followed by a strong  
eruption with angled jets reaching about halfway up the rock embankment.

I am hopeful that the short intervals and event cycles similar to  
those seen in prior years will result in many more chances to see Fan  
& Mortar in 2008.  With this in mind, we were reminded that Fan &  
Mortar are located in a bit of a "hole" for the FRS radios, and relay  
calls would be greatly appreciated by those who are in the cabin area,  
Visitor Center, and government area.  If you happen to be somewhere in  
between--even at Grotto--you're more likely to be heard at the other  
end of the basin than the person who is at Fan & Mortar.


--Tara Cross
fanandmortar at hotmail.com

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