New Lightning-Struck Tree from June 29

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These photographs show a large fir tree which was hit by lightning the morning of June 29, exactly two weeks ago.

Apparently nothing caught fire, but the tree sploded pretty good.

For whatever reason, Ponderosa pine trees and fire trees seem to be affected differently by lightning around here.

A Ponderosa struck by lightning more characteristically shows a “zipper” mark, where just the outer bark is peeled from the tree in a long vertical strip, sometimes straight up and down, sometimes cork-screwing or jumping to another object.

Fir trees, though, sometimes explode like the one shown here.

There may be nothing to this observation.  There certainly are exceptions, and to the extent there’s anything to it there are no doubt many factors involved.  How root physiology affects the propagation of the ground leader, for instance.

In both cases, the mechanism by which the tree is damaged is an instantaneous steam explosion, touched off as the lightning bolt passes through and super-heats water in the conducting materials.

In the case of the pine tree, the bolt seems to pass closer to the cambium layer, between the bark and the relatively dry sapwood.  Hence the fairly shallow blast, generally just affecting the outer bark.

In the fir tree, though, the bolt seems to go deeper into the sapwood, and the steam explosion causes much more damage to the tree trunk as it looks for a path of least resistance from the center of mass.

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