On Thu, 12 May 2005 12:41:36 -0700, "Pounds on Wood"
wrote:

I think the easiest way to understand it is this - think of a flat sawn
board. As a woodworker, you know the board will shrink most in width, a
little less in thickness, and almost not at all in length. It is the
difference in shrinkage between width and thickness that matter. Then think
of that board within a round log. Because the log is shrinking radially
greatly, but in diameter only slightly, the fibers are pulled apart radially
around the log.

Not a scientific explanation, but an easy one to grasp.

That's an excellent explanation. It also accounts for why the splits
are wider, further from the center.