Columnar Jointing

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From: John & Jan Lahr (johnjan@lahr.org)
Date: Sun Jan 26 2003 - 17:04:14 PST 

Message-Id: <5.1.0.14.2.20030126175418.017f2128@mail.attbi.com>
Date: Sun, 26 Jan 2003 18:04:14 -0700
From: John & Jan Lahr <johnjan@lahr.org>
Subject: Columnar Jointing

Last summer during the "Geology of Earth and other Planets" TI class I
tried to duplicate
a demonstration of columnar jointing that had worked at my house in
Golden. The idea is
to make some oobleck and let it dry. The cracks that form at the surface
due to shrinkage
as the oobleck dries out propagate down in to the oobleck as the rest of it
dries and shrinks.
This leaves columns of dry corn starch, just like those at Devil's
Postpile, CA.

I tried to speed up the drying process by microwaving the oobleck --
definately a bad idea!
I also tried putting the dish of oobleck under low pressure -- also a poor
idea. What I didn't have
time to do was just wait a few weeks for it to slowly dry out. Even though
SFO is more
humid than Golden, CO, I think it would eventually dry out and form columns.

I've added a page to my web site with photographs so that you can see what
it looks like
when this demonstration works.

http://jjlahr.com/science/earth_science/jointing/

If anyone tries it, let me know if it worked and how long it took. One
word of caution,
the oobleck will look and feel quite dry long before it is thoroughly
dry. At that stage
there will be no columns!

Cheers,
John Lahr

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