Volcanic eruptions can result in a series of amazing and violent natural phenomena. They can spew streams of lava, generate cloud vortexes, and blanket the sky in thick black ash. And sometimes, when ash particles collide at high speeds, the resulting friction causes bursts of lightning.

Volcanologist Corrado Cimarelli and his colleagues at Ludwig Maximilian University in Munich, Germany study the lightning events that can occur in volcanic plumes. One of the tools they use is a lab volcano simulator, or shock tube—a three-centimeter-wide vent and a hot, pressurized metal tub that propels real volcanic ash obtained from various volcanoes, including the active Popocatépetl in Mexico and Eyjafjallajökull in Iceland.

The shock tube mimics the kind of pressure found in magma chambers of active volcanoes by accelerating the ash particles at high enough speeds so that the friction from collision allows them to become charged.

In the video below, you can watch the plume turn from a wispy white to a menacing black. Tiny lightning bolts start to flicker and flash in slow-motion in the column of volcanic ash, the shock tube generating lightning up to tens of centimeters in length.

From a series of experiments in 2013, Cimarelli found that smaller particles of ash create a higher number of lightning bolts, BBC News reported in 2014. Most recently, Cimarelli and his research group studied the activity at Mount Sakurajima this year and found that the frequency of flashes also varies with the amount of ash spewed into the atmosphere during the eruption.

The researchers believe they can understand more about volcanic eruptions by surveying and monitoring volcanic lightning.

The lightning “is a parameter that can be measured—from a distance of several kilometers away and under conditions of poor visibility—and it can be used as a proxy to estimate the total mass and the size distribution of the ash deposited in the atmosphere,” Cimarelli said in a university statement about the investigations of Mount Sakurajima. “This would enable us to rapidly assess the distribution of ash particles in the atmosphere and if necessary alert the aviation authorities.”

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