[Geysers] Geyser report from New Zealand

[Ron Keam]

I should like to add some comments to those of Katherine.

I cannot recall how much I have said on this list about my concerns 
that operating the lake level of Ohakuri Lake in too aggressive a 
manner could well destablilise the Orakeikorako geothermal system and 
lead to induced hydrothermal eruptions there - to the danger of 
residents and visitors.  I was too late to be able to appeal about 
the consent to Mighty River Power, but I was able to join existing 
appeals, which related to monitoring, by two other interested 
parties.  As a result Mighty River Power have agreed to fund 
monitoring to see whether or not little hydrothermal eruptions are 
already occurring under L. Ohakuri.  The idea is to set up an array 
of hydrophones in the lake, and an array of geophones on land 
adjacent to the lake, to look for the implosion effects of steam 
bubbles produced by small hydrothermal eruption steam bubbles 
condensing in the cold water of the lake.  I have believed for some 
time that waves at Rotomahana previously attributed to seismic 
activity are more likely to have been produced by unrecognised 
under-water hydrothermal eruptions than by small shallow earthquakes, 
and that such events might be occurring also at Lake Ohakuri.  The 
reason for using both hydrophones and geophones is to be able to 
distinguish between earthquakes and such eruptions, since the ratio 
of the amplitudes of the hydrophone and geophone pulses would be 
different for the two processes.  So that is the best I think that 
can be done at present.  The interesting prospect is what should 
happen if the investigation does indeed show that small hydrothermal 
eruptions are occurring beneath Lake Ohakuri?  The risk should be 
able to be calculated if there are sufficient of these putative 
events occurring.  But even if no such events are identified it does 
not mean that induced hydrothermal eruptions cannot occur - only that 
the risk is not as high as feared.  Evidence exists of several 
prehistoric hydrothermal eruptions having occurred at Orakeikorako 
and this underlines the fact that almost all sizeable intense 
hydrothermal systems in New Zealand are subject to such instabilities.

With regard to Paul Strasser's comment, Minginui geyser is submerged 
beneath about five to eight metres of lake water.  Before it was 
drowned in 1961 Minginui went through a time when it would erupt but 
to heights of only about 2 or 3 metres.  Much more spectacular were 
the eruptions of neighbouring Rahurahu Geyser (or "Terrific Geyser") 
which in 1893 was the largest geyser in New Zealand at that time, and 
a photograph of it in action can be seen in Ted Lloyd's bulletin on 
Orakeikorako.

Ron Keam

>In answer to Paul Strasser's comments re Orakeikorako and the Ohakuri dam:
>
>Unfortunately, any idea of removing the Ohakuri dam cannot be entertained
>for at least another 20 years or so.  The dam owner, Mighty River Power
>(MRP), was granted consent a few years ago by Waikato Regional Council to
>continue operating the Waikato River hydro-electricity system.  I don't
>remember how long the consent duration is, but it will be somewhere between
>20 and 35 years.  At the consent hearing I presented evidence on behalf of
>the council, on the effects of the hydro system on the geothermal features
>at Orakeikorako and almost all the other geothermal systems in the Waikato
>Region.  However, the council did not seek lowering of the lake level, just
>the status quo.  MRP presented evidence that I strongly disagreed with, that
>lowering the lake level to natural levels would not lead to a return to the
>natural behaviour and appearance of the submerged springs.  They had done a
>big-dollar deal with the Maori land owners and the proprietors of the
>tourist area, which led to withdrawal of their (owners and proprietors)
>submissions against the proposed new operating regime, which actually
>involves increasing the lake level at times, and increasing the rate of
>change in lake level on a diurnal basis.
>
>Currently under the Waikato Regional Plan, having an existing dam in place
>is a permitted activity, meaning that there can be no requirement to remove
>the dam.  Regional Plans have to be reviewed every ten years, so once the
>current plan becomes fully operative, hopefully 2006, the review process
>will start all over again soon after, as it takes years to complete.
>
>It will be interesting to see what attitudinal changes influence the new
>process once it starts.  International interest in the planning and
>consenting processes would also be well-received and could influence the
>decision-forming.
>
>Further background information on the Regional Plan, and possibly even the
>MRP consents, can be obtained from the Regional Council website.
>
>regards
>Katherine Luketina
>
>>  -----Original Message-----
>>  From: geysers-bounces at wwc.edu [mailto:geysers-bounces at wwc.edu]On Behalf
>>  Of Paul Strasser
>>  Sent: Wednesday, 21 December 2005 17:21
>>  To: 'geyser observation reports'
>>  Subject: Re: [Geysers] Geyser report from New Zealand
>>
>>
>>  I hope that in the spirit of Ron Keam's comments (the part that follows)
>>  he's all in favor of removing the dam at Orakeikorako.  I'd love to see
>>  Minguini Geyser erupt.
>>
>  > Paul Strasser
-- 


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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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