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Flashes in the Ashes: What Is Volcanic Lightning?

A thunderstorm caused by a volcano? Find out more about this strange and awe-inspiring weather phenomenon called volcanic lightning!

Some rare and interesting weather phenomena make headlines, that are both terrifying and awe-inspiring.

On April 22, 2015, when Chile’s Calbuco Volcano erupted, a massive cloud of gas and ash billowed over 40,000 feet into the air. And while the main attraction was the volcanic blast, scientists began paying attention to the rare and unusual phenomenon known as a “dirty thunderstorm” that was occurring, complete with bolts of lightning crackling in and around the ash plume.  This volcanic lightning event is only caused by large eruptions.

Similar events happened with the eruptions of the Sakurajima volcano in southern Japan and the Eyjafjallajökull volcano in southern Iceland back in 2010.

Volcanic Lightning & Dirty Thunderstorm Explained

Eyjafjallajökull volcano - 2010 eruptions of Eyjafjallajökull

So what is volcanic lightning and a “dirty thunderstorm”? It’s a rare occurrence that scientists don’t fully understand. In a normal thunderstorm, rain clouds containing ice crystals have positive and negative charges, and when the two charges collide, a giant spark ignites within the cloud – this is what we see as lightning and hear as thunder. Scientists believe that volcanic ash particles are themselves electrically charged, and their projection into the air with such force from the eruption causes them to collide, and as a result, electrical discharges occur.

According to, “what is mostly agreed upon is that the process starts when particles separate, either after a collision or when a larger particle breaks in two. Then some difference in the aerodynamics of these particles causes the positively charged particles to be systematically separated from the negatively charged particles. Lightning is the electrical flow that results when this charge separation becomes too great for air to resist the flow of electricity.”

In the video below, watch for the bolts of volcanic lightning flashing in and around the Chilean Calbuco Volcano’s thick plume of dark ash.

Lead photo: The Eyjafjallajökull volcano in southern Iceland, April 19, 2010 Photo by Marco Fulle, from

Other ways volcanoes affect the weather

This article was published by the staff at Farmers' Almanac. Interested in becoming a guest author? Contact us to let us know!

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