Taal’s eruption illuminates volcanic lightning for scientists

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By Alka Tripathy-Lang, Ph.D. (@DrAlkaTrip)
 

Temblor talks to scientists Alexa van Eaton and Chris Schultz about the science behind bursts of lightning that lit up social media during Taal’s recent eruption.
 

Citation: Tripathy-Lang, Alka (2020), Taal’s eruption illuminates volcanic lightning for scientists, Temblor, http://doi.org/10.32858/temblor.076

On Jan. 12, 2020, Taal erupted. In the evening, as the ash plume pushed into the atmosphere, volcanic lightning commenced, Credit: Etrhamjr
On Jan. 12, 2020, Taal erupted. In the evening, as the ash plume pushed into the atmosphere, volcanic lightning commenced, Credit: Etrhamjr

The January eruption of Taal, in the Philippines, mesmerized the world as people near the volcano posted images to social media of lightning shooting from the ground to the sky, or flickering through billowing clouds of ash. For scientists who study volcanic lightning, this imagery is invaluable to the development of volcanic lightning as an eruption monitoring tool.

Alexa Van Eaton, a U.S. Geological Survey (USGS) volcanologist, and Chris Schultz, a research meteorologist at NASA Marshall Space Flight Center, both study volcanic lightning. They too were in awe of Taal’s eruption and resulting lightning show, and describe the science behind this captivating phenomenon.

 

Back to (lightning) basics

Water is a necessary ingredient for ice-charging, the mechanism that drives lightning during regular thunderstorms, says Van Eaton. In a typical non-volcanic storm, water from lower altitudes vaults to freezing heights in gusts of upward-moving air. As ice-laden air plummets back down, the frozen particles bump into each other, and into tiny droplets of liquid water. This rubbing and chaffing causes particles to lose or gain electrons, creating positive or negative charges. In the turbulent cloud, these particles separate into pockets of similar charge. As the charged regions grow, they create an electric field, which is unstable. To neutralize the instability, the positive and negative particles in each region suddenly reach toward one another, and our eyes see a flash of lightning.

 

Animation by the National Oceanic and Atmospheric Administration (NOAA) showing an example of how lightning from a typical thunderstorm may occur. As the negative charge gets close to the ground, shown in blue, a positive charge, shown in red, reaches up to meet the negative charge. Credit: NOAA Scijinks
Animation by the National Oceanic and Atmospheric Administration (NOAA) showing an example of how lightning from a typical thunderstorm may occur. As the negative charge gets close to the ground, shown in blue, a positive charge, shown in red, reaches up to meet the negative charge. Credit: NOAA Scijinks

 

During a volcanic eruption, a gas-rich plume of ash bursts from the vent, rising up to many tens of kilometers. With volcanic lightning, says Van Eaton, the ice-charging mechanism for lightning formation is similar to that of thunderstorms, and requires water to be present in the plume. But that mechanism only happens if a plume reaches high enough into the atmosphere for water to freeze.

However, a second mechanism—silicate charging—also occurs in volcanic plumes, unlike in regular thunderstorms. “When tiny rock particles rub together at high speed, they create a charge,” says Van Eaton, just like fresh laundry out of a clothes dryer. And, she says, silicate charging can happen low down in the plume where particles are most heavily concentrated—not just in the highest levels of the ash clouds.

 

Variations of volcanic lightning

When explosive ash plumes do not reach high enough into the atmosphere to freeze, silicate charging is thought to be responsible for the lightning that we see. Such volcanic lightning can occur within seconds of an eruption, while the plume is still hot, says Van Eaton.

For large, water-rich eruptions that punch ash high into the atmosphere, the lightning becomes much more intense. High flash rates can occur aloft within the vertical column and umbrella cloud near the volcano, says Van Eaton, and some flashes even follow the ash as it blows downwind.

Electrically, volcanic lightning has similarities to ordinary thunderstorm lightning, says Van Eaton, but it’s likely a combination of both ice- and silicate-charging. In a recent study lead by Van Eaton, she and her coauthors examined globally detectable lightning from the eruption of Bogoslof volcano in Alaska. They found that ash plumes reaching colder heights consistently resulted in more volcanic lightning. She says, “We are seeing the ice-charging mechanism coming into focus only when the plumes rise above the local freezing height. Once that happens, the plume transforms into a dirty thunderstorm.”

 

Taal’s eruption

The eruption began around 11:00 a.m. local time on Sunday, Jan. 12, 2020, when the Philippine Institute for Volcanology and Seismology (PHIVOLCS) noted increased seismicity. They briskly raised Taal from Alert Level 1 to 4 (out of 5) over the course of the afternoon and early evening. At 5:30 p.m., PHIVOLCS reported a “tall 10- to 15-kilometer steam-laden tephra column with frequent volcanic lightning,” which corresponds with Van Eaton’s observation that lightning was intense during the vigorous eruption, and quiet when the eruption waned.

Reports of volcanic lightning associated with lava fountains continued through Tuesday, Jan. 14, although steam and ash plumes reached much lower altitudes of 2 kilometers or less during this period. On Jan. 26, PHIVOLCS reduced Taal to Alert Level 3, and on Feb. 29, to Alert Level 2, where it remains as of this writing.

 

Taal’s lightning show

Some of the most spellbinding videos from Taal show ground-to-cloud flashes. According to Schultz, many of these videos capture intriguing lightning processes in action.

In one slow-motion video posted on Twitter, originally posted on Instagram by @franckeydelenard, lightning appears to shoot from the ground upward into the plume. Near the vent, “there is a large amount of charged rock, ash and other materials being jettisoned into the atmosphere,” says Schultz. He explains that this generated lightning near the vent that followed a continuous path of charged materials up into the plume, resulting in ground-to-cloud lightning.


 

In another arresting video of Taal’s lightning, posted by twitter user @JendukManoballs, a short flash in the ash plume immediately precedes ground-to-cloud lightning that again starts from the surface and snakes its way upward. Schultz explains that the initial short flash high up in the plume likely changed the electrical field just above the ground. A probable direct response to that change is the subsequent upward lightning flash, which is similar to upward flashes that have been observed coming from communication towers and wind turbines near thunderstorms. Schultz says that this mechanism may explain many instances of lightning observed outside the main ash plume at Taal.


 

In a video originally posted by Twitter user and photographer @joshibob_, which Van Eaton used for a Twitter crash course on volcanic lightning, the flashing, roiling cloud is reminiscent of a crystal ball high in the atmosphere. Schultz explains that in this case, numerous short flashes with low intensities dazzle our eyes (or cause a headache) because the whirling clouds create small pockets of charge that trigger tiny lightning flashes.

 

Using the imagery

“Intense volcanic lightning is not something we witness every day,” says Van Eaton. “These big events have a lot to teach us.” The videos documented by numerous “citizen scientists” are valuable for revealing how lightning evolves during an eruption, and for uncovering new ways to monitor the severity of volcanic hazards.

Scientists are still asking fundamental questions about volcanic lightning, says Van Eaton. For Taal, scientists can use these images “to revisit other eruptions we’ve studied that lacked the benefits of video footage.” According to Van Eaton, “The boom in citizen scientists with mobile phones and social media is changing the way we learn about natural phenomena.”

 
 

Further reading

Bruning, E. C., & MacGorman, D. R. (2013). Theory and observations of controls on lightning flash size spectra. Journal of the Atmospheric Sciences, 70, 4012–4029. https://doi.org/10.1175/JAS-D-12-0289.1

Montanyà, J., van er Velde, O., & Williams, E. R. (2014). Lightning discharges produced by wind turbines. Journal of Geophysical Research: Atmospheres, 119, 1455-1462. https://doi.org/10.1002/2013JD020225

Van Eaton, A. R., Schneider, D. J., Smith, C. M., Haney, M. M., Lyons, J. J., Said, R., Fee, D., Holzworth, R. H., & Mastin, L. G. (2020). Did ice-charging generate volcanic lightning during the 2016-2017 eruption of Bogoslof volcano, Alaska? Bulletin of Volcanology, 82, 24. https://doi.org/10.1007/s00445-019-1350-5

Visacro, S., Guimaraes, M. & Murta Vale, M. H. (2017). Features of upward positive leaders initiated from towers in natural cloud-to-ground lightning based on simultaneous high-speed videos, measured currents, and electric fields. Journal of Geophysical Research: Atmospheres, 122, 12,786-12,800. https://doi.org/10.1002/2017JD027016

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