A Tongan volcano plume produced the most intense lightning rates ever detected

"The eruption of Hunga Volcano was the largest volcanic explosion since Krakatau in 1883," said Sonja Behnke, of Los Alamos National Laboratory's Electromagnetic Sciences and Cognitive Space Applications group and author on the paper.

Powerful volcanic eruptions produce ash plumes that can create their own weather systems, providing the conditions for lightning at higher altitudes than normally seen. When the undersea volcano in Tonga erupted, it created a plume that went more than 25 miles higher than typical thunderstorms. Lightning was observed at stratospheric altitudes (12 to 18 miles), where the air pressure is too low to support thunderstorm-like lightning. This fast-rising volcanic plume may have created locally higher pressures to support the environment necessary for lightning.

After reaching its maximum height, the plume expanded outward as an umbrella cloud, creating fast-moving circular ripples known as gravity waves, similar to a rock dropped in a pond. Donut-shaped rings of lightning expanded with the umbrella cloud and were as large as 174 miles in diameter. Similar "lightning holes" have been observed in thunderstorms, but never on this large of a scale.

The lightning was detected by space-based optical sensors, and global networks of ground-based radio antennas thousands of miles away.

The research team, led by the US Geological Survey Cascades Volcano Observatory, found that the eruption produced 2,615 flashes per minute at its peak intensity, which lasted nearly five minutes. This peak lightning rate is significantly higher than the second most intense lightning event ever detected -- 993 flashes per minute -- in a thunderstorm over the southern United States in 1999.

Remote detection of lightning helped create a detailed timeline of this historic eruption, and demonstrated the value of using volcanic lightning for monitoring volcanic activity.

"Lightning observations such as these reveal detail about the evolution of an eruption over time, which is particularly valuable when cloud-cover obscures satellite observations of a plume," said Behnke.

The work was supported by the U.S. Geological Survey Volcano Hazards Program, the Laboratory Directed Research and Development program at Los Alamos National Laboratory and a NASA ROSES-2019 "Earth Science Research from Operational Geostationary Satellite Systems" program award.