[Aztlan] Question for Ron - On Yaxchilan Geography

[Elaine Day Schele]

Hi Ron,

Thanks for that first hand information Ron.  I had wondered about how the
bridge might have (or could have) been able to line up vertically on the
Guatemalan side.  A question comes to mind about the path and erosion of the
river of which you might be able to answer.  Under most circumstances,
rivers erode and change because of the meandering of the water and due to
deposition caused by the force of the water...so the banks usually change
drastically (like the river in this picture
http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/fluvial/oxbow_lake_small.jpg).
I have been told that in the case of parts of the Usumacinta the position of
the river, has not changed for hundreds of years, due to its underlying
geology.  In other words, the omega where Yaxchilan sits will never erode
and become an oxbow like the one in the picture linked above.  But on the
Guatemalan side - do you know if it is possible that the bank on the
Guatemalan side to have eroded down?  Do you remember seeing any evidence of
it when you were there last?

Thanks,
Elaine

----- Original Message ----- 
From: <Ronald.L.Canter at faa.gov>
To: <aztlan at lists.famsi.org>
Sent: Wednesday, May 09, 2007 3:16 PM
Subject: [Aztlan] Fw: Reply to Aztlan Digest, Vol 18, Issue 8. On Suspension
Bridges, esp. one at Yaxchilan


>
>
>
>
> Reply to Aztlan Digest, Vol 18, Issue 8.
>
> Suspension Bridge at Yaxchilan
>
>       After spending a little time studying the waterfront at Yaxchilan
> locating stones grooved by long use as moorings, I also looked at the Maya
> suspension bridge proposed by James O'Kon.  Though a very appealing
> concept, I have to say that I am not convinced.  The suggested bridge
lines
> up well horizontally with the hieroglyphic staircase in the Main Plaza,
but
> there are problems with the vertical lineup.
>       The staircase leads to the top of Structure 5, which is 22 meters
> above average low water stage.  This is on river-left, the city side.  On
> river-right, the Guatemalan side, the river terrace level is much lower,
> 12.6 meters above low water.  There should be the remains of an approach
> ramp and a sturdy anchoring structure 10 meters high on the Guatemalan
> side, but there is nothing.  The floor of the bridge would have been at
the
> height of Structure 5, not only to connect but also to rise well above the
> normal bankfull stage, which is not coincidentally 12.6 meters above low
> water.  Since the bridge floor would have gone through (not on top of)
> them, support towers would need to be at least 28 meters high - on a 10
> meter base (the width of El Pilar).  Such tall, thin towers are very
> unusual in Maya architecture, and unprecedented for ones placed right in a
> swift river.
>       This does not mean the proposed suspension bridge was impossible,
> just that the parts don't seem to fit well.
> Ron Canter
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