The Science Behind Volcanic Lightning: Unraveling the Mystery

Physicists have unraveled the mystery behind volcanic lightning occurrence. Why do some particles become positively charged while others become negatively charged during friction?

This phenomenon, known as the triboelectric effect, explains how electrical charges transfer when two surfaces make contact, such as hair being attracted to a balloon after rubbing.

Within a volcanic ash cloud, silicon dioxide particles clash, leading to charge exchanges, which results in lightning when positively and negatively charged particles separate, creating a flow of electric current.

However, physicists struggled to explain the asymmetry between identical material particles that causes charge flow in varying directions.

“Numerous factors are suspected to influence this,” states Galien Grosjean, a researcher at the Autonomous University of Barcelona. “We’ve found that humidity, surface roughness, and crystal structure play important roles.”

During his research at the Austrian Institute of Science and Technology in Klosterneuburg, Grosjean proposed that carbon-containing molecules present on the particle surfaces could hold the key. While materials scientists aim to eliminate these contaminants, Grosjean and his team focused on how washing affected particle charging.

Using ultrasound, they suspended small silicon dioxide particles, allowed them to rebound off a plate of the same material, and subsequently measured their charge. “You can observe either a positive or negative charge. Washing or heating the positively charged sample often reverses its charge,” explains Grosjean.

The analysis revealed that the presence of carbon-containing molecules significantly influenced the charging direction. “This factor proved more critical than any others,” Grosjean emphasizes.

Notably, cleaned samples regain a positive charge within approximately 24 hours due to the swift accumulation of new carbon molecules from the surrounding air.

Daniel Lux from Case Western Reserve University commended the research. “While it’s common knowledge that surfaces collect dust, this finding is unprecedented in the realm of triboelectrification,” he commented.

However, Lux expressed concerns that this discovery could complicate future predictions for physicists. If carbon contamination determines charge direction, accurately predicting particle charge could become nearly impossible. “Such predictions might turn out to be unrealistic,” Lux added.

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