[Geysers] Eruption at Ngatamariki, NZ

[Ashley Cody]

Hi Cindy

I'll put answers in your text after each part.


----- Original Message -----
From: "Cindy Rose" <crose61514 at wyoming.com>
To: "geyser observation reports" <geysers at wwc.edu>
Sent: Friday, April 22, 2005 1:14 PM
Subject: Re: [Geysers] Eruption at Ngatamariki, NZ


> Ashley--
>
> I am interested in the climate of this zone--with pines you automatically
> think temperate but of course pines can grow in subtropical areas too.

Our climate in central North Island is temperate, although we are just
getting into
our winter and we had 6" of snow on main highway just south of Taupo last
night,
only ~200 miles south of me in Rotorua.
>
> Also, what is the base rock for this explosion feature? Is it volcanic or
> sedimentary, or even hyrdothermal precipitate on top of some other
bedrock?

At Ngatamariki the eruption was sourced from silicified fine silty tephras.
Blocks of this up to 0.6m dia. (~2 ft for Americans?) thrown out. Surface
exposures expose up to about 20 m thick deposits of pumice gravels, all
loose and unconsolidated. The ejected blocks of rock had pronounced
shrinkage or cooling shattering cracks evident. This I suspect was due to
cooling from about 150 deg. C down to ambient of ~15 deg. C in a few
minutes; the cooling stresses and shatters rocks. I've seen this often
before too. From the feel and texture (and from doing 100s of XRD analyses
of thermal rocks) I think the majority of stuff was montmorillonite clay. It
swells and shrinks greatly on wetting and drying so it too shatters rocks as
it weathers on land surface.

Hope this helps. Can send you some photos if you want! Best wishes on your
YNP trip! (lucky thing!).

Regards
Ashley Cody



>
> Thanks!
> Cindy
>
>
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