Why Does Lightning Sometimes Cause Trees To Explode?

Trees explode when struck by lightning because wood is a relatively poor conductor of electricity, so as the bolt forces a current through the trunk it generates enormous heat (a lightning channel reaches roughly 30,000 K, about five times hotter than the surface of the Sun). The water and sap inside the wood flash to steam in microseconds, and the resulting pressure wave can blow the bark off or split the trunk apart entirely.

You’ve almost certainly seen cartoons and caricatures depicting people being struck by lightning. Similarly, you might have also seen pictures of trees (or even trees in real life) that have been struck by lightning. When humans are struck by lightning, it generally causes burns and several other injuries (some of which might even be fatal), but lightning-struck trees are often cut in half or in rare cases, they even explode! How does that work?

How does lightning cut trees in half, but in the case of humans, lightning strike victims don’t generally lose their limbs?

The answer to this question lies in how lightning interacts with humans and trees, respectively.

Recommended Video for you:

What Happens When A Human Is Struck By Lightning?

You might already know that a lightning strike is basically just a powerful flow of electrons (albeit the process of its buildup is quite interesting).

It’s obvious that lightning strikes are particularly dangerous for any living creature, including humans. The human body, or any other living thing, is simply not built to conduct hundreds of kilowatts of electricity!

When a lightning bolt strikes a human, an electric current that briefly peaks in the tens of thousands of amperes (with the bolt itself carrying around a billion joules of energy in just a few microseconds) courses through their body. This, needless to say, has rather unpleasant and painful effects on the body.

Interestingly, however, humans are reasonably good conductors of electricity, especially compared to wood. You might have heard that humans are composed of “70% water”; as such, the human body does not offer as much resistance to a huge electric current as you might expect. The body (and the fluids inside it) have decent conductivity once the lightning has punched through the relatively resistive outer skin; consequently, the passage of even a huge electric current does not generate as much heat as it would if it were to pass through a higher-resistance material (like a tree). A great deal of the strike’s energy also tends to flow over the wet outside of the body, a phenomenon called flashover, which is a major reason most lightning-strike victims actually survive.

Thus, when lighting strikes a human, the body becomes a ‘passage’ for the former to run straight into the ground. However, since humans do offer some resistance, lightning victims are often known to suffer from severe burns, nerve tissue damage, shock or cardiac failure (some of these may even be fatal).

Now, let’s take a look at what happens in the case of trees.

What Happens When Lightning Strikes A Tree?

It is quite common for trees to be struck by lightning, and what’s even more unfortunate is that there is nothing they can do about it. A tree struck by lightning may behave in unpredictable ways: some trees look absolutely normal following a lighting strike, while others explode or burst into flames! The reason lightning strikes are (often) so brutal to trees is the resistance they offer to the flow of electricity as it passes through them.

You see, unlike humans, trees are not good conductors of electricity. As such, they offer a lot of resistance to the flow of electricity through their ‘body’. You might recall from your high school Physics class that when there is high resistance to the flow of current, heat is produced in the system. The same thing happens in the case of trees.

The trees’ resistance to the flow of electricity causes a high heat built-up as lightning travels through a tree’s frame. Such insanely high temperature can sometimes cut trees in half.

In fact, some trees will even burst into flames or explode following a lightning strike. This is because during a lightning strike, the sap in the bark of the tree is subject to extreme temperatures, many times hotter than the surface of the Sun, in fact! The electrical resistance causes the sap to be overheated into steam, which can make the tree explode instantaneously.