[Geysers] Blog post about geyser mechanisms

[Karen Webb]

Have you got a detailed description of your set-up that could be posted? 
Zayne's old enough now that we could attempt to have Webb family 
driveway experiments, and this looks like a neat set-up if you can 
compare overflowing/non-overflowing and vertical vs. horizontal.
Karen


On 9/8/2013 10:33 PM, Carlton Cross wrote:
>
> What you describe sounds like what I remember.  Jeff may have 
> something to add if my memory needs correction.  (I haven't had time 
> to dig up our old data.)
>
> There are many features of a geyser's plumbing that will affect the 
> frequency of oscillation, the main ones being the combined volume of 
> the bubbles, the mass of the water above the bubbles, and the size and 
> friction of the passage leading to the surface.  Smooth pipes that are 
> cooled by the outside air are not very good models of geyser plumbing, 
> but I think it's interesting that the behavior of the models can be 
> seen in some natural geysers.   I don't remember finding a geyser that 
> displayed the rapid bouncing, but that is no surprise because the 
> friction in a natural geyser tube is much greater than in a smooth 
> pipe and the mass of the moving water is generally greater.  As the 
> friction increases, the frequency of oscillation will decrease; and, 
> as the moving mass increases, the frequency will decrease.  I can't 
> think of any reason why a natural geyser would oscillate faster than 
> the models.
>
> Carlton Cross
>
> cross at bmi.net
>
> *From:*geysers-bounces at lists.wallawalla.edu 
> [mailto:geysers-bounces at lists.wallawalla.edu] *On Behalf Of *Demetri 
> Stoumbos
> *Sent:* Sunday, September 08, 2013 5:24 PM
> *To:* Geyser Observation Reports
> *Subject:* Re: [Geysers] Blog post about geyser mechanisms
>
> I find it interesting that your experiments produced two distinct 
> patterns of water column bouncing.  In my backyard modeling 
> experiments, I have found that the system starts out with the "rapid" 
> form of bouncing, and then progressively shifted to the "slow" form. 
>  I noticed this both in models which overflowed between eruptions, and 
> those in which the water level naturally sat a little bit below 
> overflow.  As the eruption neared, the bouncing would decrease in 
> bounces per second, increase in amplitude, and become more erratic. 
>  That is to say that a water level vs time graph would start out 
> looking like a sinusoidal wave, but then the ordered nature of the 
> curve would deteriorate as time went on as the water level stalled for 
> split seconds or bounce around at peaks and troughs.  Of course in the 
> overflowing systems, the actual water level was constant at vent 
> level, so I went off of how much water overflowed per unit time.  In 
> these systems, as the bouncing progressed to "slow" form and its 
> amplitude grew during an interval, the low parts of the bouncing would 
> become low enough that overflow would momentarily stop (think 
> Depression or Oblong).
>
> I guess my end question is: did your models show an either/or pattern 
> in relation to the two forms of bouncing, or did they start out with 
> the "rapid" form, then at one point flip over to "slow" form?
>
> Demetri Stoumbos
>
> On Sun, Sep 8, 2013 at 2:32 PM, Carlton Cross <cross at bmi.net 
> <mailto:cross at bmi.net>> wrote:
>
> A quote from the below link,
>
> "There, after an eruption, more and more steam can accumulate between 
> the surface of the water and the roof of the cavity, gradually 
> building up pressure. When the pressure grows too high, the steam and 
> water escape through the geyser's vertical shaft."
>
> and
>
> "They found that pressure builds up in a bubble trap there between 
> geyser eruptions, just as in the Russian study."
>
> I haven't had time to locate and read the referenced sources,  but I 
> think it's important to note that pressure build-up is not what causes 
> an eruption.  Also, the Cross driveway experiments have produced 
> geyser models that demonstrate eruptions from an entirely vertical 
> system with no places for trapping steam.  Pressure gages along the 
> water column show clearly that the pressure everywhere decreases 
> continuously once the eruption has started.  The temperature also 
> drops because the steam carries heat out of the system.  Eruptions in 
> a vertical system were not noticeably different from those of a 
> horizontal system.
>
> The static pressure within a fluid system is determined by the depth 
> below the surface.  When you dive into water, you feel greater 
> pressure as you go deeper.  It doesn't matter whether you're in a 
> chamber with vapor or not.  In a horizontal chamber, the static 
> pressure will be determined by the pressure at the chamber exit to the 
> surface, and the pressure at the exit will be determined by the depth 
> below the surface.  As a geyser system fills after an eruption, the 
> depth of the water increases until the start of overflow.  After that, 
> the temperature will increase, but not the static pressure.
>
> Steam within a horizontal chamber will displace water from the 
> chamber.  That water must exit through whatever passage leads to the 
> surface where overflow will occur.  Hence, the effective depth of the 
> water above the chamber will not change and the static pressure will 
> NOT increase.
>
> Once a geyser system has reached overflow, it can and does continue to 
> heat, and, at some point, a small section of upward-moving water will 
> rise until it reaches a place where the static pressure is low enough 
> for the water to boil and produce steam.  The expansion of the steam 
> will displace water from that region, and, simultaneously, the steam 
> bubbles will begin to rise.  As the bubbles rise in the water column, 
> the static pressure at all points below the bubbles will decrease 
> because water with bubbles weighs less than water without bubbles. 
>  Finally, when the pressure drops, the boiling point drops and more 
> water will boil which produces more bubbles which allows more water to 
> boil, etc.  The system has gone unstable and the expanding steam will 
> begin to rush toward the surface exit - an eruption.
>
> So far, I have talked only about the static pressure which is 
> determined by the depth within the system.  There are, of course, 
> dynamic pressure changes related to water movement.  Once steam has 
> accumulated within a chamber or the water column, the whole column can 
> bounce up and down because the steam below is compressible.  When the 
> column rises, the steam expands and the pressure drops eventually to 
> the point where the upward motion will decrease, possibly until it 
> stops and then begins to fall.  The downward motion will compress the 
> steam below and the pressure will rise, possibly causing the steam to 
> condense into water.  When the pressure is finally great enough to 
> stop the downward motion, expansion can begin again, pushing the water 
> upward.
>
> Our driveway experiments clearly produced two forms, rapid and slow, 
> of a bouncing water column as the system neared an eruption.  In the 
> rapid form, there was only slight movement of the water at about one 
> cycle per second with no overflow.  The slow form was more like a 
> series of overflow surges separated by many seconds.
>
> Carlton Cross
> cross at bmi.net <mailto:cross at bmi.net>
>
>
>
>
>
> At 07:38 PM 9/7/2013, you wrote:
>
>     Thinking this might interest some gazers who do not read
>     geological magazines or journals, I'll send along the URL to a
>     post I just put up about some interesting new studies on geysers:
>
>     <http://www.yellowstonetreasures.com/author-blog/>http://www.yellowstonetreasures.com/author-blog/
>
>
>
>     Happy geyser gazing to those of you who get to enjoy the late season!
>
>     Janet Chapple
>
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