Right- and Left-handed Cracks

A scientist coworker and occasional contributor to the Forum, Professor Hans Nielsen, recently noticed that dead spruce trees near his house on Yankovich Road show cracks that spiral in only one direction--clockwise looking down towards the base of the tree. This observation led to a minor after-supper investigation of the subject to see if all cracks are as Professor Nielsen reported.

One finding is that it does not matter which end of the tree one looks at. If the cracks spiral in one sense as seen from the top of the tree, the sense is preserved when viewing from the bottom. They are the same as threads on a bold or rod, either right-hand or left-hand. To screw a nut on a right-hand thread, one turns the nut clockwise regardless of which end of the rod is attempted.

Secondly, not all cracks in local spruce trees spiral in the same sense. Of more than a hundred examined from several localities, 68 percent showed cracks spiraling in the same fashion as right-hand screw threads, only 12 percent showed left-handed spiraling and 20 percent showed straight cracks. Clearly, there is a strong tendency towards crack spiraling in the right-hand sense.

So far none of us has come up with a plausible-sounding explanation for the preponderance of right-hand spiral cracks. Can any readers do better?