[Geysers] Blog post about geyser mechanisms

[Carlton Cross]

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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