Volcanic eruption plumes sometimes develop lightning storms
Volcanic eruption plumes sometimes develop lightning storms. The detection of radio waves generated by these storms can help warn of hazardous ash, yet little is known about how volcanic plumes become electrified. Using the 2020 Taal eruption in the Philippines as a case study, Alexa Van Eaton of the US Geological Survey and colleagues developed a conceptual model for how plumes with high water content can become electrified.
The eruption of Taal volcano on 12 January 2020 was phreatomagmatic, meaning there was interaction between magma and water
The eruption of Taal volcano on 12 January 2020 was phreatomagmatic, meaning there was interaction between magma and water. In this case, a large water-rich ash plume rose 17 km above sea level and spread out as an umbrella-shaped cloud. The team used a combination of satellite imagery, time-lapse photography and a global dataset of radio waves generated by lightning to investigate volcanic-lightning production.
Their results show that lightning was only detected globally once the plume reached >10 km above sea level, where the lightning flash rate increased to over 70 flashes per minute as the plume expanded vertically and laterally. The authors suggest that at these higher altitudes, water freezes within the plume, leading to intense electrification, like regular thunderstorms. Ground-based photos showed hundreds of tiny flashes and blue-coloured ‘streamers’ at the umbrella cloud base. The team propose that enhanced electrical activity occurs in this region because the flow changes from vertical to lateral movement, which helps separate different regions of charge. Their model suggests that initial electrification occurs by collisions of ash particles near the volcanic vent, but lightning here is not globally detectable, contrary to the higher altitude ‘thunderstorm-like’ lightning. The 2022 eruption of Hunga submarine volcano in Tonga produced a record level of lightning, which this conceptual model may now help to understand.
Taal produced many plume-to-ground lightning strikes within 20-30 km from the volcano – a region inhabited by over 1.2 million people. Therefore, this research not only helps to inform the different processes of lightning formation in water-rich eruptions, but also emphasises the hazard of volcanic lightning in densely populated areas.
- Geology, In Press 2022; doi.org/10.1130/G49490.1
Lucy Blennerhassett is a PhD student studying environmental geochemistry, volcanism and climate change at Trinity College Dublin, Ireland