[Geysers] Colour changes and colour effects in thermal features

Ron Keam r.keam at auckland.ac.nz
Tue Dec 12 18:25:04 PST 2006


Pat Snyder's contrasting photographs of Pearl Geyser show probably 
the most dramatic change I have ever seen in the colour of a 
geothermal feature (apart from occasions when formerly transparent 
water has become clouded due to some stirring of sediments).

In 1951 Frying Pan Lake at Waimangu was almost an indigo colour and 
the water was clear enough for a submerged crater rim to be quite 
clearly visible.  By the late 1960s the water had assumed a greener 
tinge and was much cloudier.  Only once in recent years have I seen 
it clear again and that state did not last.  The hinterland at 
Waimangu was turned into farms in the late 1950s and I can believe a 
suggestion made to me that the effect has been produced by run-off of 
fertiliser that had been liberally spread there to increase 
agricultural productivity in what formerly had been a very lightly 
vegetated pumice soil.

Inferno Crater Lake changes cyclically in colour in synchronism with 
its level changes - when the water is rising it is very turbid and a 
very pale brown colour; during a main flow it is blue but mostly 
difficult to see because of the dense steam-clouds hiding it; during 
the long recession after a main flow it clear and the most intense 
turquoise colour.  The muds being deposited within the Inferno Crater 
basin were brilliantly snow-white in the 1950s.  Now they are a 
rather less attractive light brown.  (Once when I was conducting an 
experiment to test its possible interconnection with Frying Pan Lake, 
Inferno Crater Lake was artificially turned red with Rhodamine B 
flourescent dye.  Afterwards the dye adhered to the mud flocculating 
in the water, and deposited out as a distinct band which persisted 
for a few years.  It all disappeared long ago.)

Those of us who were privileged to be taken in Rick Hutchinson's boat 
out onto Grand Prismatic Spring saw some of the clearest water in any 
thermal spring that I have ever seen.  The rocks at the bottom 
started off in the shallower regions appearing green, and gradually 
as the depth increased they appeared to be bluer and bluer, and 
ultimately becoming almost indigo and the bottom became invisible. 
The contrast with the waters in Frying Pan Lake and Inferno Crater 
Lake was very distinct.

There is a very green lake in one of the craters of the Waiotapu 
thermal area near Waimangu.  This lake has the Maori name Rotowhero 
which means "Red Lake".  One should not suppose that the name was 
applied by a colour-blind person, because there are significant 
deposits of red mud around, and the supposition is that the name was 
originally given when this mud had been stirred up in the lake waters.

Ron Keam

>Thank you, Stephen, for mentioning the color change in Pearl. Here 
>is a picture "before" (September 2004) and "after" (September 2006). 
>Both are beautiful in different ways, but I do miss the blue 
>opalescence.
>Enjoy.
>Pat Snyder
>
>Sept. 2004:
>
>
>Attachment converted: Macintosh HD:pearl9.9.04web.jpg (JPEG/8BIM) (00120AEB)
>
>Sept. 2006:
>
>
>Attachment converted: Macintosh HD:pearl9.6.06.jpg (JPEG/8BIM) (00120AEC)
-- 


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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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