At 11:00 AM 8/11/2008, Louise Power wrote:
On the news this weekend, they called it "geology at work." Hope
nobody was hiking underneath when it happened.
When Mt. St. Helens blew up people were all agast at the devistation
and destruction and how terrible it was to human and animal life.
That's a pretty biased and one-sided view and a slap in the face of
geology which was hard a work just tending to normal business.
I call it "land building"--geology at work, doing what it's supposed
to be doing: Building mountains and then moving them to the sea--one
grain at a time if need be. Geology doesn't give a damn if anybody
was hiking under the arch at the time it fell or not. People are
mostly insignificant vectors in the overall scheme of geologic
things--they help out a bit by tumbling rocks down the hillside
(getting them closer to the sea) whilst road building or just hiking,
or they throw rocks into the river whilst entertaining themselves
skipping stones. Otherwise human beings are of little concern in
geologic time or to geologic forces. Future limestone will contain
rubber tires and lost boat motors and mafia exiles encased in
concrete blocks--stuff like that.
Freeze/thaw cycles on the surface of the rock play an important part
in the first stages of rock degradation there, Fritz. At least in
places where it freezes--like Utah. But you can't discount the daily
expansion/contraction due to the temperature changes in the ambient
atmosphere around the arch when considering what actions weakened it
enough to make it fall. Daily expansion and contraction (over a range
on the order of 50 or more degrees) would, I think, play a lot larger
part in the eventual blowing apart of a (nominal) monolithic chunck
of extremely exposed sandstone along internal joints and other zones
of weakness by eventually crunching itself into smaller and
subsequently insubstantial pieces, at some point being unable to
support itself any longer.
That global warming (even though it was introduced to this discussion
as a subtle joke unnoticed by some humor impaired readers) could have
a very real effect on the differential values of expansion and
contraction due to thermal changes in the dynamic atmosphere must be
considered, and in a big way--no matter what is causing global
warming this time around.
Doing my part for global warming,
--Ediger
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