Re: [Paddlewise] Cliff Notes

From: "Dave Uebele" <daveu_at_sptddog.com>
> 
> Assuming a perfectly shear cliff, acting as mirror, 1/4 wavelength
> into the wall, plus 1/4 wavelength coming back to you, adds up to
> 1/2 wavelength.  So right at that spot, the reflected wave will be cancelling
> the next incoming wave.    Go out to 1/2 wavelength from the cliff,
> and now the 1/2 plus 1/2 add up to a whole wavelength, and the waves
> will be twice as big.
> 

I had an interesting experience this summer at Lake Superior Prov. Park,
in the north part of Agawa Bay.  Amie and I paddled around and went to 
see the rock paintings on the cliff.  When paddling back to the cove from 
which we'd launched, I found the water was rough, with big waves, followed
by relatively calm, though with big waves nearby.  After thinking about
it, I realized what was happening.

The cliff was a long convex curve to the north of the rock paintings.  The
reflected waves were being dispersed by the curved cliff, in much the same
way that light is dispersed by a convex mirror.  These waves interfered 
with the incoming waves to form a pattern of rough and calm areas.  We 
were paddling along a line that took us through alternating areas of 
smooth and rough water.  You could find an illustration of this in any 
college text (physics or engineering) that deals with vibrations and waves.

Mike


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