[Geysers] Fw: Rotorua Blowout

[Ron Keam]

Ashley's report about the eruption is not at all surprising 
considering the history of this particular location.  For those 
readers who have a copy of GOSA Transaction Volume VII a sketch of an 
1894 blow-out there appears as an illustration on page 166 and a few 
details are given in the text on the same page.

A rather simplistic study (commenced several years ago but 
uncompleted) indicated that such blowouts would be particularly 
likely on sediment flats through which geothermal fluids at boiling 
temperature were being discharged.  (This is almost "obvious".) 
Certainly both on the flats at the mouth of the Puarenga Stream, and 
also on the old Frying Pan Flat (before 1917) such physical 
conditions prevailed, and hydrothermal eruptions are (were in the 
case of FPF) a characteristic feature.  It is perhaps surprising that 
no historical events like this have occurred, however, on the present 
"Frying Pan" area at Waiotapu, and there are no obvious remnant 
features that would indicate such had occurred there in relatively 
recent times.

Ron Keam

>
>----- Original Message -----
>From: <mailto:ashley.cody at wave.co.nz>Ashley Cody
>To: <mailto:geysers at wwc.edu>geysers at wwc.edu
>Sent: Monday, February 07, 2005 11:29 AM
>Subject: Rotorua Blowout
>
>A brief note from Rotorua NZ. On Tuesday 18 January a hydrothermal 
>eruption was witnessed by a member of a Maori dance group who were 
>gathering outside Lake Plaza hotel, on the shore of Sulphur Bay. 
>They were about 1 km west (~0.5 mile) from site, which was at mouth 
>of Puarenga Stream at its delta into Lake Rotorua. Area is a big 
>expanse of boiling solfatara (~10 acres?) with a long history of 
>such eruptions.
>
>The one on Tuesday 18 January sent up a vertical column of steam as 
>a big mushroom cloud, that suddenly appeared and caught attention of 
>people outside hotel. They thought it went about 30 m high and after 
>a few minutes all died away. I visited site last week and there is a 
>new crater ~15m diameter, boiling and overflowing 2-3 litres/sec. 
>Blocks of ejecta <0.5m dia. thrown to <10m away and muddy debris to 
><25m radius of crater rim. I have photos of this and could e-mail 
>them to anyone (~20 Kb jpegs?) if you e-mailed me at 
><mailto:codya at wave.co.nz>codya at wave.co.nz
>
>In Whakarewarewa Village, a ground collapse occurred in early 
>January between the main hot spring Parekohoru and the Oil Baths. 
>Area ~10 x 15m has sunken by up to 2m into boiling hot pools, 
>waterlevels ~2m below surface. Area has a long historical record of 
>ground subsidence and is where a colleague got badly scalded in 
>early 1970s when ground collapsed under him. At present a tourist 
>footbridge spans part of this collapse and is main access to hot 
>baths. Bridge is closed now and myself and an engineer have the job 
>of deciding if any sort of bridge can be built to access the baths 
>(and can they afford to build it?). I am very apprehensive about any 
>on site and in ground geotechnical investigations and may decide it 
>is too much risk to even do that.
>
>Ashley Cody
>
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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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