Volcanic Lightning Could Help Geologists Monitor Eruptions

In 79 A.D., Pliny the Younger witnessed the eruption of Mount Vesuvius firsthand. Several years later, he chronicled the devastation in a series of letters, detailing not only the “shrieks of women, the wailing of infants, and the shouting of men,” but the furious forces of nature evident at the scene, including “frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame.”

Although the plumes of black smoke and roaring flames described by Pliny likely align with the average person’s vision of a volcanic eruption, lightning—overshadowed by the terrifying image of lava spewing forth from a volcano’s top—often fails to make the cut. Still, Maya Wei-Haas reports for National Geographic, these electric tendrils offer more than just a spectacular light show. According to a new study published in the Journal of Volcanology and Geothermal Research, lightning could help researchers better monitor eruptions by providing insights on volcanoes’ behavior in near real-time.

Scientists from Portland State University, the United States Geological Survey (USGS), the University of Washington and the National Oceanic and Atmospheric Administration drew on the World Wide Lightning Location Network’s database of lightning activity at 1,563 active volcanoes, as well as satellite imagery capturing volcanic plume expansion, to track lightning rates at various points during an eruption.

The team found that the number of lightning strokes crackling through the sky peaked as an eruption underwent initial intensification and fell as the plume steadily expanded, suggesting that spikes in activity mark key changes during the early stages of eruptions.

Lightning analysis has several advantages over traditional monitoring methods, according to Wei-Haas. Researchers typically rely on seismometers to gauge potential volcanic threats, but such tools are difficult to install and maintain, meaning they’re often placed by volcanoes bordering communities rather than those in remote areas. Unfortunately, relative isolation doesn’t preclude risk, as aircraft flying above remote volcanoes can be hampered by volcanic ash.

Satellite imagery and infrasound are two other options, but both have downsides: Clouds or darkness can hide key clues to imminent eruptions, and the sound waves used in infrasound can get jumbled as they move across hundreds of miles. Lightning detection, on the other hand, is speedy (even outpacing eyewitness reports) and less susceptible to weather obstacles. As study co-author Alexa Van Eaton, a volcanologist at the USGS Cascades Volcano Observatory, tells National Geographic, light also avoids the potential distortion experienced by sound waves.

Volcanic lightning has long mystified scientists. Writing for The Washington Post in 2016, Angela Fritz explains that it’s difficult to catch lightning in action, as strikes only occur at the beginning of the most intense eruptions.

In general, lightning serves as a correcting mechanism for negative and positive charges separated in the atmosphere. When lightning strikes, such charges are neutralized. Scientists know that the culprits behind your average thunderstorm are electrified ice crystals, but until recently, the exact science behind volcanic lightning remained a mystery. Then, in 2016, two studies separately published in Geophysical Research Letters outlined promising explanations for the singular phenomenon.

As Becky Oskin notes for Live Science, one report focused on video footage, infrasound and electromagnetic analysis related to Japan’s Sakurajima volcano. Combined, the data suggested that static electricity generated by particles rubbing together in thick clouds of ash was responsible for volcanic lightning. The second study, which was also led by Van Eaton, focused on the April 2015 eruption of Calbuco volcano in Chile. Interestingly, the team recorded distinct similarities between volcanic lightning and thunderstorm lightning; despite the seemingly contradictory nature of an icy volcano, Van Eaton and her colleagues found that water vapor-filled clouds of thinning ash produced ice that triggered lightning much like a thundercloud does.

In conjunction with the newest findings, the 2016 studies offer ample evidence of lightning’s importance in tracking volcanic activity. But as Rebecca Williams, a volcanologist at the University of Hull who was not involved in the study, tells National Geographic’s Wei-Haas, questions—including the issue of how well WWLLN’s network of sensors distinguish between storm and volcanic lightning—remain.

“Further work needs to be done to fully distinguish the two types, but there is great potential here,” Hull says.

Van Eaton echoes this sentiment, telling Wei-Haas that additional research must be conducted before the method is adopted for popular use.

“What we really have with this paper is some juicy observations,” Van Eaton concludes. “I hope that this will trigger a lot of interesting modeling work, and people who can take these observations and take them to the next level.”

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's associate digital editor, history.