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What Causes Volcanic Lightning?

What Causes Volcanic Lightning?

After 42 years of silence, the Calbuco volcano in Chile has again roared to life. Earlier this week, the volcano started spewing untold tons of ash and magmatic material as high as 33,000 feet (10 kilometers) into the atmosphere. Lava flows glow red on its 2,000-meter-high (6,500 feet) face. A stunning timelapse of the initial eruption on Wednesday has since gone viral:

Chile’s emergency and geological agencies have declared a wide exclusion zone around the volcano, and more than 4,000 people have been evacuated. Smoke and fog and ash has put a grey blanket on the surrounding areas. You can see the ash plume from space.

But as with other heavily-photographed volcanoes, like the Sakurajima Valcano in southern Japan or the Eyjafjallajökull volcano in southern Iceland, maybe even more stunning than the towering plume or glowing lava is the lightning that can crackle from inside the ash. As nights have fallen on Chile, Calbuco has come alive as well. But what brings the lightning to a volcanic eruption?

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The Phenomenon That Sounds Like A Sex Move

Over the last century or so, well over 100 different eruptions around the world have had recorded lightning in their ash clouds. And it’s not a fluke — there don’t just happen to be thunderstorms above every one of these volcanoes. No, look closely at any photograph of the phenomenon, and the lightning begins and ends in the plume itself.

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For something that looks like ancient gods battling over a fiery cauldron, volcanic lightning doesn’t have the most epic name: a dirty thunderstorm. I don’t even want to know what the Urban Dictionary entry would be on that.

But unlike lightning that happens in a thunderstorm, which we don’t quite know the origin of, a dirty thunderstorm…no, I’m not saying that…volcanic lightning seems more straightforward. What causes a blinding streak of electricity to rip through an ash cloud is a charge separation.

Have you ever rubbed your feet on a carpet and then sparked a friend with your finger? You just created a charge desperation that resolved itself on the face of your friend. Rubbing your feet along the carpet covers you in negatively charged electrons, and if you do it vigorously, you’ll be carrying enough electrons that the charge difference between you and a surface without that same charge will be too great. Those electrons will “jump” to the lower potential. That’s the spark you feel (and sometimes see).

Volcanic lighting (and the lightning we’re more familiar with) is like this on a giant scale. Pieces of earthen material come flying out of a volcano (probably) carrying a charge along with them. As the gargantuan cloud encounters the atmosphere, those particles tumble and bump together, creating even more charges. Then, the particles are separated based on the aerodynamics of the particles inside the ash plume itself. When the charge difference becomes untenable, lighting rips through the cloud to neutralize it.

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A “dirty thunderstorm” might not be the most appealing name, but there isn’t a light show like it on Earth.

IMAGES: David Cortes Serey/Martin Berenetti/AFP/Getty Images

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