Video: Volcanic lightning captured in a bottle

Spark of inspiration (Image: Lucas Jackson/Reuters)

It’s a “build your own volcano” kit like no other. A team of geologists in Germany has built a model volcano that crackles with lightning as it erupts. But this is no toy science kit for kids – it could offer insights into the disruption risk to aircraft in the aftermath of an eruption.

Volcanic lightning was first documented by Pliny the Younger following an eruption of Mount Vesuvius in AD 79. The exact cause of the lightning remains unclear. Previous work suggests that ash particles slam into each other as they are ejected from the vent, generating a frictional charge. So Corrado Cimarelli at Ludwig Maximilian University in Munich, Germany, built a model volcano to mimic this charging process.


They took ash from recent eruptions, including the infamous 2010 eruption of Iceland’s Eyjafjallajökull, the ash cloud from which grounded European flights for weeks. They put the ash in a tube and held it there at 100 times atmospheric pressure before venting it through a nozzle into a large tank filled with air at normal pressure, mimicking the sudden release of pressurised material from a volcanic vent.

Lo and behold, their tiny volcanic eruptions generated lightning sparks, which they recorded with high-speed video. The finer the ash particles, the more lightning the team recorded.

The videos helped explain this relationship. They showed that if the particles were relatively large – about 500 micrometres in diameter – they shot vertically upwards out of the nozzle. Smaller particles were more likely to be caught up in the turbulence around the nozzle, making them more likely to collide and generate frictional electrical discharges – a tiny version of spectacular volcanic lightning.

“We are convinced that the fundamental process of charge-discharge is the same, no matter the scale,” says Cimarelli.

Controlled chaos

Tamsin Mather a volcanologist at the University of Oxford, is impressed with the work. “What’s really nice is the way they have controlled particle-size distribution, which obviously is a parameter you can’t control with a real live volcanic plume,” she says. “The results will inform future measurements of real volcanic eruptions.”

Cimarelli says the results may be particularly useful for predicting the disruption to air traffic following an eruption. This is because there is such a clear correlation between the number of lightning discharges and the concentration of fine ash particles, meaning it may be possible to quickly estimate the fine ash content of an eruption by monitoring the amount of volcanic lightning. It is this fine ash that is most likely to rise to aircraft-cruising altitudes, 9 kilometres above sea level, where it can disrupt air traffic.

The study is not the final word on volcanic lightning, though. “The mechanism is one of several likely [ones],” says Steve McNutt at the University of South Florida in Tampa.

For instance, Mather points out that while the lightning recorded in the experiments is indeed similar to that seen at or near the vent of a real volcano, there is another form of volcanic lightning that occurs further above the volcano, known as plume lightning. This form is probably triggered by collisions with ice crystals high in the atmosphere, similar to a normal thunderstorm, she says.

Journal reference: Geology, DOI: 10.1130/G34802.1