When Lightning Strikes a Tree

Why does lightning strike trees?

Lightning likes to strike trees because trees offer a nice conductor that gets the lightning into the ground with the minimum of resistance.  The key to this power of trees is the water they contain.  A heathy tree will have a lot of water just under the bark for the lightning strike to follow.  Older or damaged trees may have some rot that tends to accumulate water, sometimes offering the best conductor in the center of the tree’s trunk.  If a tree has been soaked with rain just before the lightning strikes,  the water on the outside of the bark may offer the path of least resistance.

What happens to the tree when lightning strikes?

The bottom line for the tree is where the water is concentrated.  If it’s on the bark, the tree may not be damaged at all.  If it’s just under the bark,  the outer layers of the tree may be scarred.  If it’s deeper in the trunk, the tree may be blown to pieces as the water rapidly expands from the heat of the lightning bolt.  There are a lot of ‘mays’ there because it’s hard to predict what might actually happen to a tree when it is struck by lightning.

The photo below shows a tree I recently came across while backpacking around Waldo Lake in Central Oregon.  Take a close look then, read on.

 

 

First, notice the missing top of the tree.  The lightning blew it off of and away from the tree.  Also notice the raw wood around the top – it’s missing it’s bark and some of the wood is missing as well.  Second, notice the missing bark spiraling around the tree.  That’s the path of the lightning and the scar it left when it blew off the bark and some of the underlying wood.  Third, notice that this tree has the largest diameter trunk in the area.   A larger trunk diameter suggests a taller tree and one more likely to be struck by lightning.  Finally, notice the piece of raw, white wood, just to the right of the tree at ground level.  More on that in a second.

Here’s a photo of some of what was on the ground around the tree:

That big chunk of wood was once the top of the tree.  It was deposited on the ground ten feet away from the tree trunk.  Notice how it is broken apart and smashed.  The lightning did some of that and the remainder was caused by the fall to the ground.  If you look carefully at the ground in the photo, you will see pieces of fresh wood scattered all around.  Pieces like this were scattered in all directions around the tree suggesting that they were blown off by the lightning and not just the result of the top falling to the ground.  That fresh wood to the right of the tree trunk in the top photo was the largest piece like that around.  It was embedded in the ground.

The Moral of the Story

If you are in a forest when a lightning storm blows in, you may not be able to decide which tree is most likely to be struck by lightning – although the one with the largest trunk is likely to be the tallest and a good candidate for a lightning strike.  All you can do is try to get away from the tallest trees, follow the advice provided in my “Lightning Safety” post, and hope for the best.  This story reinforces the dangers of being under a tree.  Not only will you be endangered by the lightning, but you also face the prospect of a falling treetop and flying wood debris.  Either of which could cause as much or more damage than the lightning itself.  The moral: when lightning strikes a tree, you don’t want to be nearby.

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