In the dark of night, ominous lightning flashes above the slopes of an erupting volcano. However, most eruptions do not produce a stunning show in the sky, so volcanic lightning is a rare spectacle to see. Furthermore, scientists are unsure how this natural phenomenon occurs, but volcanic lightning has been documented for the past 200 years. The most recent eruption witnessed by scientists occurred at Eyjafjallajokull in Iceland. They studied the blast and conducted multiple experiments to determine how volcanic lightning occurs.
Science Behind Volcanic Lightning
Sakurajima Volcano in Japan
Volcanologists at Ludwig Maximilian University in Munich published a study in the Geophysical Research Letters where the recorded the volcanic lightning that occurred when Sakurajima erupted. They compared the video to infrasound and electromagnetic data collected. They found that thick clouds of ash produce static electricity. These particles rub together, which results in a charge buildup that generates lightning. This phenomenon is called triboelectricity.
Eyjafjallajokull in Iceland
Scientists studying the eruption of Eyjafjallajokull found that lightning produced by volcanoes is similar to how lightning occurs in thunderstorms. To create lightning, there has to be a significant separation of charge between two masses. Separation of charge allows the air to ionize for an electrical current to travel through it. In contrast to ordinary thunderstorms, charge separation occurs mainly due to ash. When the volcano first releases ash, the ash is electrostatically neutral. However, the ash particles come into contact with each other, which produces a frictional force that creates a charge. This phenomenon is similar to how rubbing a balloon on your hair generates an electric charge. However, while a balloon displaces a few electrons, more than 1020 electrons are needed to create lightning. Therefore, volcanic lightning occurs more frequently in eruptions that thrust bigger plumes of ash into the atmosphere because it increases molecular collisions that displace electrons.
Type of Lightning
The lighting produced by volcanic eruptions can come in many shapes and forms. Some of the most iconic types are St. Elmo’s fire, sheet lightning, and bolt lightning. In some rare cases, there is a combination of most of those types. During the eruption of Mt. St. Helens in 1980, the sky dazzled onlookers with sheet lightning accompanied by St. Elmo’s fire the size of a car.
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Resources: http://volcano.oregonstate.edu/volcanic-lightning, https://www.livescience.com/54443-how-volcanic-lightning-works.html, https://www.forbes.com/sites/startswithabang/2018/02/09/how-do-volcanoes-make-lightning/#7e2f93774cac
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