[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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