If you’ve ever seen a video of a volcanic eruption, then there’s a good chance that you might’ve seen one or more lightning bolts appearing within or around the ash clouds of the eruption. If you haven’t been paying attention, here’s a gif to bring you up to speed:
Those images obviously make me think – why do lightning bolts appear after a volcanic eruption? Is a volcano powerful enough to cause a lightning strike?
In short… yes, it is. Volcanic lightning is believed to be caused by the interaction of charged particles present in the ash cloud and the bottom of normal clouds. However, before we dive into the cause behind this mysterious and beautiful phenomenon, we should cover a few basics first.
What causes lightning?
Lightning is essentially an electric current, only with a huge magnitude. Just like in household appliances, electric current is created through the movement of microscopic charged particles; similarly, lightning is also caused by the interaction of these charged particles.
You see, the air near the ground is warm, which makes it rise. As the warm air rises, the water vapor cools and forms a cloud. Note that this is a perpetual process, i.e. the warm air continues rising and the clouds keep getting bigger. However, the temperature at the top of these clouds is not particularly high; on the contrary, it’s quite chilly up there! This drops the temperature of the water vapor below the freezing point, causing it to turn into ice.
It just so happens that these tiny ice crystals perpetually bump into each other while moving, which builds up an electric charge. Lighter, positively-charged particles rise to the top of the cloud, while heavier negatively-charged particles sink to the bottom. When the cloud grows big enough and the warm water droplets coming up from the bottom meet the ice coming down from the top, these oppositely charged particles interact and ZAP!… lightning occurs. (Note: the explanation of the entire process of lightning involves a lot of technical and more specific details, but for the scope of this article, this basic understanding of how lightning works will suffice.)
Where does lightning occur?
Typically, lightning occurs high in the sky, either between clouds or inside a cloud. Such lightning strikes occur all the time and, as you might have guessed, we’re generally not concerned about them. What we really care about is the bolt of lightning that strikes the ground.
As mentioned earlier, the negatively-charged particles sit at the bottom of the clouds that move over the ground. Sometimes these clouds attract positively-charged particles from the ground itself. These positively-charged particle move up tall objects like telephone poles, skyscrapers and even trees to meet the ‘stepped ladder’ of negatively-charged particles descending from the clouds. Here’s a gif of a slow-motion lightning video captured at 6,200 frames per second:
How can volcanoes cause lightning?
Now that you understand how lightning works (especially lightning that’s caused by interaction with the ground), understanding ‘volcanic lightning’ shouldn’t be too difficult.
First of all, it should be noted that scientists have yet to determine the exact cause of volcanic lightning. Volcanic eruptions are too infrequent and their locations too remote for researchers to make comprehensive observations. Furthermore, the dense clouds of smoke that are released after a volcanic eruption obscure most lightning flashes, making it even more difficult to ascertain if lightning has occurred in the first place. Still, there are a few logical hypotheses that explain these rare and remote phenomena.
Volcanic lightning can be divided into two phases. The first is the eruptive phase, which is represented by lightning that forms instantly after the eruption. This is thought to be caused by the interaction of the positively-charged particles ejected from the volcano and the negatively-charged particles at the bottom of the clouds.
The other phase is plume lightning, which is seen as the lightning formed in the ash plumes at locations downwind of the crater. It is this phase of lightning that we know the least about, but researchers believe that the plume itself might play host to some sort of charging process, which charges the particles inside it and then interact with the heavy, negatively-charged particles at the bottom of the clouds.
All in all, it’s fair to say that we don’t completely understand the formation of volcanic lightning, but the most widely accepted belief is that it must be caused by the charged particles present within the ash clouds as they move through the atmosphere.