Volcanic lightning is the lightning that crackles out of the dark, apocalyptic clouds billowing out of volcanic eruptions. It looks like a surefire sign of the end times, but it’s actually a fairly common, scientifically grounded phenomenon. However, it’s one that has only ever been understood in the broad strokes, with its finer details eluding scientists.
A new study published in Nature is helping fill in one of those gaps.
The static electrical effect that makes a balloon cling to your hair or sweater is called triboelectric charging. Volcanic ash is mostly made up of identical silicon dioxide particles. It shouldn’t easily exchange charge because there’s no difference between the colliding materials. Yet in real eruptions, these particles charge up anyway, generating lightning.
Scientists Finally Figured Out How Volcanic Lightning Happens
The new research suggests that there is a thin, almost invisible “film” of carbon-based molecules that coats ash particles. These molecules accumulate naturally from the environment, turning particles into chemically distinct surfaces. That tiny difference is enough to enable charge transfer when particles collide, jumpstarting electrification and ash cloud.
There are other factors at play. Ice formation factors in, especially as ash plumes rise and cool. In higher altitudes, ice crystals interact with ash like they do in thunderclouds, significantly increasing lightning activity. Early in eruptions, water vapor head particle collisions kick-start the process, and then freezing conditions amplify it.
To test their theories, researchers re-created ash interactions in the lab, bouncing silicon dioxide particles against similar surfaces under controlled conditions. Even in these super-simplified setups, carbon contamination overrode other variables such as humidity or particle height, indicating that microscopic surface chemistry is a much bigger factor in the formation of volcanic lightning than previously assumed.
All of this has implications well beyond volcanic lightning. Several industries and scientific processes rely on controlling static charge. It was previously assumed that clean, uniform materials were involved. The study suggests that might not be the case. Even in tightly controlled experiments, surfaces accumulate molecular debris that can change how materials behave.
In other words, the thin layer of chemical dirt and grime covering molecules might be responsible for the giant, terrifying crackling bolts of lightning firing out of inky black smoke plumes firing out of volcanoes.
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