The 'Hazard Beam'

If a curved branch straightens for some reason, it can split and produce a 'hazard beam'. Claus Mattheck in his book 'The Body Language of Trees' describes the process in detail.

One way of looking at the problem is as follows:

Distance 'B' is longer than distance 'A'.

If the branch straightens, the length of  'B' can not be 'squashed' into its new space (which now equals distance 'A') so the branch has no choice but to buckle outwards and form a split within the branch.

The term 'delaminate' describes the process of the branch splitting and separating along the grain.

As the branch bends,  the wood along  'A'  is in tension (it is being pulled from each end) while the wood within  'B'  is being compressed together. If  the wood within  'A'  was very weak (decayed) it would fracture and   'B'  would probably fold over.

The following photograph of such a branch failure was taken on a site in Oxfordshire. The tree is a Sycamore and the break is probably as a result of decay.

This photograph was taken early in the New Forest (complete with an audience)! The tree is an Oak (Quercus robur). The original course of the curved branch can be seen if you follow the upper edge of the remaining bark.

The following photograph was sent in by Pete Kenyon.  It was shot on Mt Einos at Kefalonia and the tree appears to be Abies cefalonica (which is apparently unique to the island).