[Geysers] Three geysers of note

[Ron Keam]

I would agree with Jeff's comment, judging from my own experience 
with geysers in New Zealand.

Examples:

Rotomahana lake has no natural surface outflow.  Its water level is 
therefore controlled by rainfall and evaporation and percolation.  As 
its water level rises and falls in response to rainfall patterns 
particular suites of geysers along the lake margin become active or 
become dormant. and the suites are consistent - perhaps with some 
delay in becoming re-established when there has been prolonged 
dormancy.  (Such delay can be attributed to the rising water needing 
to heat sufficiently the rock with which it is coming into contact.)

At Orakeikorako, the sinter-covered flat known as "Artists' Palette" 
has of order 60 to 70 vents in it.  Many of these from time to time 
become discharging springs and even geysers, and usually these active 
features are grouped.  At any given time the water level varies from 
place to place under the flat and with the progress of time the 
higher portions move their locations.  I am not aware of any project 
having been undertaken to study why this is so.  Sometimes almost the 
whole flat has water discharging from the features, and at other 
times the discharging features are very limited in extent.

Significant redistributions of heat flow have been apparent in 
portions of New Zealand thermal areas, this is indicated by 
vegetation becoming prolific or dying off in particular places.  I am 
personally aware of this having happened at two places at Waimangu. 
One very large area which supported very little vegetation on 
"Rainbow Mountain" (Waiotapu thermal area) before the 1886 Tarawera 
eruption is now well covered, and it is now hard to see the coloured 
earth from which the feature received its name.

Ron Keam

>I suspect that most changes in geyser activity are caused entirely by changes
>in the subsurface water and heat flow patterns, not by changes in the plumbing
>system.
>
>Why do I say this?
>
>Changes in flow patterns are reversible.  Thus, geyser like Plume, Giant, Fan
>and Mortar, etc. can enter dormant phases and then recover to erupt on
>precisely the same patterns as before.
>
>Changes in the plumbing systems (blowing out constrictions, plugging channels,
>etc.) are not reversible.  Typically these involve the expulsion of sand,
>gravel, or larger blocks of sinter.  The formation of Plume's lower (largest)
>vent, the destruction of the former "Pathetic Little Hole," post-1959 Sapphire
>Pool, all represent permanent, irreversible changes.
>
>Jeff Cross
>jacross at lamar.colostate.edu
>
>>I have been thinking about Echinus and there are a couple of questions I have
>to throw out-- seems like this geyser currently has plenty of water but (?)
>has gradually lost its heat source-- Or is it possible that it has damaged
>itself like Excelsior and Monarch are speculated to have done to
>themselves?... I wondered this since Norris is the hottest basin in the Park
>and is likely to still have plenty of heat.  <snip>
>>     Mario Durrant
>>
>>     **************
>>     Quite a number of years ago we ran into a ranger on a visit to Norris, at
>the time when Echinus was first having it's problems. He said that there was a
>new feature above Echinus that had a very, very low ph- low even for Norris.
>It was running off down into Echinus' pool, and his theory was that the
>acidity was eating away Echinus' throat, thus robbing it of it's ability to
>build pressure to erupt.
>
>
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-- 


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Ron Keam
The Physics Department
The University of Auckland
Private Bag 92-019
Auckland
New Zealand
Phone +64 9 373-7599 extension 87931
FAX +64 9 373-7445
EMail r.keam at auckland.ac.nz
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