[Geysers] The role of geyserite in geyser plumbing (or "Who needs geyserite anyway?")

[JEFFREY CROSS]

I've never felt that silica precipitation along the geyser tube was a necessary feature of geysers.

The wall rock, regardless of composition, must be coherent enough to withstand the forces of rapidly moving water.  If it isn't, the walls will collapse inward from cavitation or excavation of loose sand and gravel.

The notion that silica must line the walls of the geyser to form a pressure seal is probably related to the erroneous idea that the pressure builds prior to an eruption.  As you demonstrate in your graphs, this doesn't happen at all.

One thing that gets lost in debates is that the *vapor pressure* of the geyser's water does build prior to the eruption.  When the vapor pressure (which increases with temperature) equals the confining pressure (hydrostatic + atmospheric), then a steam bubble can displace the liquid around it, and any observer would say that the water is now boiling.

Note that Steamboat Geyser, presently the biggest on earth, is also one of the youngest of geysers, having formed just after the Park was established.  How much silica can it have deposited along its tube in the relatively short time after the vent formed and before the first major eruptions happened?

Jeff Cross
jeff.cross at utah.edu


________________________________
From: geysers-bounces at lists.wallawalla.edu [geysers-bounces at lists.wallawalla.edu] on behalf of Davis, Brian L. [brdavis at iusb.edu]
Sent: Wednesday, July 31, 2013 12:12 PM
To: geysers at lists.wallawalla.edu
Cc: Davis, Brian L.
Subject: [Geysers] The role of geyserite in geyser plumbing (or "Who needs geyserite anyway?")

Why do you need geyserite to ‘pressure seal a geyser’?

We had an interesting conversation on Facebook recently about how a geyser erupts, and I managed to get myself somewhat confused (again). I was trying to point out that the pressure in a geyser conduit is never really above hydrostatic - pressure does not “build” in a geyser (at least not after it is full), and during an eruption the pressure in the conduit decreases. A lot. So I started working up a text description of an eruption in detail (right down to how bubbles of steam grow, etc.).

Then I thought about the description of the role geyserite plays in “pressure sealing” the “plumbing systems” of geysers… and wondered “why?” As near as I can tell, pressures never rises above hydrostatic. Moreover, if the plumbing system was actually ‘sealed’, there would be no way to recharge either water or energy to the system. So…

1) Is the pressure always at or below hydrostatic?
2) If so, what role does a geyserite-lined system play (vs. any other lining)?

To anyone interested in the original longish conversation, here’s a FB link to it:
https://www.facebook.com/groups/4939307398/permalink/10151566192312399/

This includes links to data from models that show the pressure never gets above hydrostatic *except* during rapid dynamic effects (like a steam-filled conduit sealed under a deep pool condensing the steam and producing a post-eruption ‘water hammer’):
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=3695302

So far the best idea I’ve come up with is that it acts to reinforce and pressure-seal the main conduit against higher *external* pressure, after the geyser has erupted… but honestly that doesn’t make a lot of sense to me, as water infiltrating from the walls seems to be one way the conduits refill in the first place, and secondly voids in rock or even semi-consolidated sediment can remain against hydrostatic external pressure just fine on their own, no “armor cladding” needed.

--
Brian Davis
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