[Geysers] Grotto discharge

[David Schwarz]

   The problem is that water is also the major conveyor of heat in this
system, as well as the thermostat.  It seems to me that it's likely that
except near the surface, the temperature of the rock in the plumbing system
is actually greater when the system is full of water than when it's empty.

   Assume that the system is full.  Water below the surface can get hotter
than the surface boiling temperature because it's under the pressure of the
hydrostatic head above it, and it will get hotter because it's receiving a
constant influx of heat from volcanically superheated water entering the
system at depth.

   When the system is "empty," the water level is actually just a long way
below the surface.  It's still there.  Any heat that reaches the rocks above
this low water level comes from steam that boils off of that water.  That
steam will be right around the surface boiling temperature of water, maybe a
little more assuming the water is superheated, which this system generally
is.  So the maximum temperature of the rock above the low water level is
barely more than the boiling point of water.  Except for the rock right at
the surface, the rock in the plumbing system will actually be able to get
hotter when it's underwater.

   But suppose the rock does get a bit hotter than the surface boiling
temperature.  As you pointed out, water has a high heat capacity--that is,
it takes a relatively large amount of energy to increase the temperature of
water compared to, say, a chunk of iron--or of rock.  That means that a
volume of water as large as the Grotto-Giant system's reservoir could easily
reabsorb the heat it earlier transferred to the rock through steam without
increasing its temperature much at all.

   My guess on Scott's observation is this:

   After a Grotto marathon, the discharge from the system of both water and
heat is very low.  It's limited to steam and, once it refills, Variable
Spring's overflow.  Maybe a few other small features.  Notably absent is the
continuous discharge by Bijou.  I remember noticing as long ago as the early
'90s that the GIP would be at its highest levels--sometimes easily visible
from the old, low boardwalk--shortly before Bijou resumed its cycles some
number of hours after the end of a marathon.  Once Bijou started, it would
recede a bit.  It's possible that after a marathon, the system recovers its
water levels faster than its heat.  That would mean that the time of the
marathon recovery hot period would actually be the time of largest water
volume in the system.  Higher stable water levels also mean a higher
hydrostatic head, which could act like a Champagne cork when pushed off by
the hot period activity.

   So basically, I'm suggesting that marathon recovery gives the system an
unusually long time to build up water and heat, and that it probably
actually reaches greater than its typical levels of one or the other, and
that that somehow make stronger hot periods--and therefore eruptions--more
likely.

   Something similar seemed to go on with Fan and Mortar in the '90s.  The
longer River Vent was off, the higher water levels got throughout the
system, and, with some notable exceptions, higher water levels in Main Vent
and Mortar before River Vent came back on usually corellated with a stronger
and longer hot period once River Vent did come back on.

David Schwarz

On 8/30/06, Moose, Allan E. <MOOSEAE at uwec.edu> wrote:
>
>  I have some thoughts on Scott's back of the envelop calculation below. It
> seems (to me)  plausible that a Grotto marathon removes water from the
> interstices below Giant and its associated geysers. Because water is an
> effective absorber of heat (that's why it's used in car radiators) and air
> isn't, the result is that the rocks around the interstices will increase
> significantly in temperature. (Think of what happens to your car when a
> radiator hose breaks.) Thus, when water fills in the voids after Grotto
> ends, there is more energy available for the recovery hot period and/or a
> Giant eruption.
>
> Now, I have a question: Is the data available to do a linear regression on
> the length of Grotto marathons and the time from Grotto's shut down to the
> recovery hot period?
>
>
> Allan Moose
>
>
> "Science is just organized curiosity"
> (Donald Kroodsma)
>  <https://mailman.wwc.edu/mailman/listinfo/geysers>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: </geyser-list/attachments/20060830/f7913f4e/attachment.html>