Volcanic lightning helps aviators avoid hazardous ash

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

A remote Alaskan volcano erupted for nine months, repeatedly disrupting aviation traffic. How can lightning help minimize ash hazards for aircraft?
 

Citation Tripathy-Lang, Alka (2020), Volcanic lightning helps aviators avoid hazardous ash, Temblor, http://doi.org/10.32858/temblor.088
 

 Plume from Bogoslof on February 19, 2017, seen from Unalaska Island, 53 miles east-southeast of the volcano. This photo, captured from a helicopter during fieldwork by the Alaska Volcano Observatory, was taken 14 minutes after this particular explosive event began. Credit: Janet Schaefer and the Alaska Volcano Observatory / Alaska Division of Geological & Geophysical Surveys

Plume from Bogoslof on February 19, 2017, seen from Unalaska Island, 53 miles east-southeast of the volcano. This photo, captured from a helicopter during fieldwork by the Alaska Volcano Observatory, was taken 14 minutes after this particular explosive event began. Credit: Janet Schaefer and the Alaska Volcano Observatory / Alaska Division of Geological & Geophysical Surveys

 

Pilot: KLM 867 heavy, we are descending now: we are in a fall!
On Dec. 14, 1989, Redoubt Volcano in Alaska began to erupt. The next day, in an effort to avoid ash clouds reported by other aircraft, KLM Flight 867 diverted from its normal route. At 11:46 a.m., the Boeing 747 inadvertently entered the ash cloud at approximately 25,000 feet. To exit the cloud, the crew decided to ascend, but after about 90 seconds, at 27,900 feet, all four engines failed. After gliding to 13,300 feet in a region where the mountains rise to as high as 11,000 feet, the crew managed to restart the engines and make an emergency landing in Anchorage, Alaska.

 

Photograph of volcanic lightning at Redoubt during its March 2009 eruption. Credit: Bretwood Higman
Photograph of volcanic lightning at Redoubt during its March 2009 eruption. Credit: Bretwood Higman

 

There were no casualties, but damage to the aircraft’s engines and electrical system from volcanic ash was more than $80 million. The National Transportation Safety Board investigated, and found, “A factor related to the accident was: the lack of available information about the ash cloud to all personnel involved.”

In recent years, scientists have developed and enhanced volcano monitoring tools, including those for stratospheric ash clouds. “Volcanic ash,” says Tom Gonzalez, a pilot for a US-based commercial airline, “is probably one of the worst things to deal with in aviation.”

 

Tracking volcanic eruptions

Alaska hosts over 50 historically active volcanoes according to the Alaska Volcano Observatory, all of which are capable of directly impacting air traffic should they erupt again. The Alaska Volcano Observatory monitors 30 of them in real time with seismic sensors placed directly on these volcanoes, but many potentially eruptive peaks lack direct monitoring because they are so remote. In these cases, scientists use additional tools to track activity, such as infrasound, satellite images, and more recently, volcanic lightning, according to Alexa Van Eaton, a volcanologist at the U.S. Geological Survey (USGS). These tools are used in concert to detect imminent or ongoing eruptions so that aviators can be alerted to any potential hazard.

 

Numerous volcanos in Alaska lack direct monitoring. In this image, taken April 30, 2020, all unmonitored volcanoes are superposed over those that are directly monitored, highlighting the risk posed by this volcanic arc. Credit: Alaska Volcano Observatory
Numerous volcanos in Alaska lack direct monitoring. In this image, taken April 30, 2020, all unmonitored volcanoes are superposed over those that are directly monitored, highlighting the risk posed by this volcanic arc. Credit: Alaska Volcano Observatory

 

One Alaskan volcano, and its recent prolonged eruption, highlights how volcanic lightning is giving scientists and aviators critical information to protect aircraft and passengers flying in regions prone to eruptions.

 

Bogosolf’s nine month long eruption

Though towering 19,500 feet (6 kilometers) above the seafloor, Bogoslof, a remote Alaskan volcano, pokes only 330-500 feet (100-150 meters) above the Bering Sea. After slumbering for more than 20 years, Bogoslof’s recent eruption began in December of 2016. This eruption lasted until August of 2017, and was punctuated by 70 explosions that produced ash plumes ranging from 13,000 to almost 39,000 feet (4 to almost 12 kilometers) above sea level, says Van Eaton.

During the months-long eruption of Bogoslof, 32 of the individual ash plume-generating explosions crackled with volcanic lightning that was detected almost instantaneously, worldwide, according to a paper lead by Van Eaton, published in the February issue of the Bulletin of Volcanology.

 

The Alaska Volcano Observatory issues volcano alerts via a color-coded system. Green indicates normal activity, with color changes indicating level of concern to aviators. In this image, taken April 30, 2020, all monitored volcanoes are are either green or yellow. Credit: Alaska Volcano Observatory
The Alaska Volcano Observatory issues volcano alerts via a color-coded system. Green indicates normal activity, with color changes indicating level of concern to aviators. In this image, taken April 30, 2020, all monitored volcanoes are are either green or yellow. Credit: Alaska Volcano Observatory

 

Detecting dirty thunderstorms

The mechanism by which volcanic lightning forms is much the same as thunderstorm lightning. Particles collide and are either stripped of their electrons or adorned with extras, becoming positively or negatively charged. As the newly charged particles separate, an electric field forms that is balanced by lightning.

For thunderstorms, ice is the necessary particle for ice-charging. In an eruption, as ash is catapulted from the vent into the tumultuous plume, silicate particles swap electrons in a process called silicate-charging. Volcanic lightning can form by either silicate charging only, or a combination of ice- and silicate-charging. The latter, which Van Eaton calls a “dirty thunderstorm,” happens when there’s an external source of water—like at Bogoslof. But how important is each mechanism?

Detection networks like the World Wide Lightning Location Network and Vaisala’s Global Lightning Dataset are designed to detect very low radio frequencies produced by lightning that propagate long distances at the speed of light, says Van Eaton. Between these two global networks, more than 4,550 volcanic lightning strokes were identified throughout Bogoslof’s eruption.

The plumes that hosted lightning shared two key characteristics—they rose above the atmospheric freezing level of water, which is —4 ºF (—20 ºC), and they were sustained for longer than 2 minutes. Higher summer temperatures drove water’s atmospheric freezing levels as high as 26,200 feet (8 kilometers), whereas in cold winter months, it dropped as low as 9,800 ft (3 kilometers). At Bogoslof, the occurrence of volcanic lightning depended strongly on altitude, implicating thunderstorm-style ice-charging as a major catalyst for Bogoslof’s lightning, says Van Eaton.

 

Plume height for each of the 70 explosions at Bogoslof, shown as red and black bars, is determined by satellite. Red bars indicate plumes that generated globally detected lightning. Dashed bars indicate unknown plume height, shown at an arbitrary altitude of 2 kilometers. Shading indicates atmospheric temperatures over Bogoslof. The darker shading shows the altitude at which the temperature was 32 ºF (0 ºC). The lighter shading shows the atmospheric freezing level of water, —4 ºF (—20 ºC). Stars indicate two plumes that generated volcanic lightning, but did not clearly rise above the atmospheric freezing level of water. However, Van Eaton and colleagues point out that both may have been higher than suggested, based on photographic evidence and measurements of volcanic gases high in the atmosphere.  Credit: Van Eaton et al., 2020
Plume height for each of the 70 explosions at Bogoslof, shown as red and black bars, is determined by satellite. Red bars indicate plumes that generated globally detected lightning. Dashed bars indicate unknown plume height, shown at an arbitrary altitude of 2 kilometers. Shading indicates atmospheric temperatures over Bogoslof. The darker shading shows the altitude at which the temperature was 32 ºF (0 ºC). The lighter shading shows the atmospheric freezing level of water, —4 ºF (—20 ºC). Stars indicate two plumes that generated volcanic lightning, but did not clearly rise above the atmospheric freezing level of water. However, Van Eaton and colleagues point out that both may have been higher than suggested, based on photographic evidence and measurements of volcanic gases high in the atmosphere. Credit: Van Eaton et al., 2020

 

Commercial airliners typically fly at or above 30,000 feet, according to Gonzalez, who has flown numerous international flights while skirting actively erupting volcanoes. “Higher is usually better, but at times you may be in the low 30,000s due to winds, turbulence, or [another] aircraft condition.” At Bogoslof, all plumes higher than 29,500 feet (9 kilometers) produced lightning, regardless of season, indicating that when the plumes were high enough to interfere with aircraft, volcanic lightning tipped off scientists to the presence of ash.

 

Photo of ash arising from the Guatemalan Volcán de Fuego, taken from the cockpit of a commercial airliner. Such spurts of ash are easily avoided by aviators, but if a large eruption begins suddenly, winds change, or an airplane is flying at night, these hazards become harder to see. Credit: Tom Gonzalez
Photo of ash arising from the Guatemalan Volcán de Fuego, taken from the cockpit of a commercial airliner. Such spurts of ash are easily avoided by aviators, but if a large eruption begins suddenly, winds change, or an airplane is flying at night, these hazards become harder to see. Credit: Tom Gonzalez

 

Combining techniques at Bogoslof

Dave Schneider, a research geophysicist at the Alaska Volcano Observatory, was first alerted to Bogoslof’s eruption as pilots flew by and notified the Federal Aviation Administration (FAA) dispatchers of peculiar activity. Once scientists knew Bogoslof was erupting, they applied their full arsenal of remote monitoring tools, including volcanic lightning detection, to evaluate the hazard to aircraft from individual explosions for the duration of the eruption.

Plume height and location – critical details for aviators – is most often deduced from satellite imagery. But in these images, Bogoslof’s plumes often lacked tell-tale ash signatures, giving the illusion that these were plumes of harmless water as ash rained on nearby settlements, as summarized in a parallel paper lead by Schneider. If an explosion at Bogoslof was accompanied by lightning, van Eaton says, “we know it was an ashy [explosion].”

 

Worldview satellite image collected May 28, 2017, showing the initial development of an ash plume shooting 40,000 feet (12 kilometers) skyward during the 2016-2017 eruption at Bogoslof. This image was captured just after the plume rose above the atmospheric freezing level of water, and 2 minutes before production of detectable lightning. The white color toward the top of the column indicates a large amount of condensed water and ice. This abundant water comes from the ocean under which the vent is submerged. Image provided under a Digital Globe NextView License. Credit: Dave Schneider and the Alaska Volcano Observatory/USGS.
Worldview satellite image collected May 28, 2017, showing the initial development of an ash plume shooting 40,000 feet (12 kilometers) skyward during the 2016-2017 eruption at Bogoslof. This image was captured just after the plume rose above the atmospheric freezing level of water, and 2 minutes before production of detectable lightning. The white color toward the top of the column indicates a large amount of condensed water and ice. This abundant water comes from the ocean under which the vent is submerged. Image provided under a Digital Globe NextView License. Credit: Dave Schneider and the Alaska Volcano Observatory/USGS

 

“Time delays for new satellite images can be up to 15 to 30 minutes depending on the satellite, and if the weather is bad, it may be impossible to see the volcanic cloud anyway,” Van Eaton says. On the other hand, detection of volcanic lightning is nearly instantaneous, no matter the visibility conditions, and in one explosion at Bogoslof, it was the sole indicator used to raise the alert level.

However, globally detectable volcanic lightning is not ubiquitous. According to Sonja Behnke, a scientist at Los Alamos National Laboratory who studies volcanic lightning, “It seems to be important to have external water to have the ice-charging mechanism.” She explains that Bogoslof has an external water source because its vent is submerged underwater. Similarly, Redoubt has a glacier at its summit, providing an external water source for ice-charging.

Van Eaton notes that another major challenge with volcanic lightning is understanding why some plumes have more than others. She points out, “Our sensor network [in Alaska] is still pretty sparse, so it’s only sensitive to major volcanic lightning events.” She continues, “This is why multi-pronged approaches are so important,” and adds that “no one method can stand alone.”

 
 

Further reading:

Behnke, S. A., Thomas, R. J., McNutt, S. R., Schneider, D. J., Krehbiel, P. R., Rison, W., and Edens, H. E. (2013). Observations of volcanic lightning during the 2009 eruption of Redoubt Volcano. Journal of Volcanology and Geothermal Research, 259, 214-234. https://doi.org/10.1016/j.jvolgeores.2011.12.010

Casadevall, T. J. (1994). The 1989-1990 eruption of Redoubt Volcano, Alaska: impacts on aircraft operations. Journal of Volcanology and Geothermal Research, 62, 301-316. https://doi.org/10.1016/0377-0273(94)90038-8

Schneider, D. J., Van Eaton, A. R., and Wallace, K. L. (2020). Satellite observations of the 2016-2017 eruption of Bogoslof volcano: aviation and ash fallout hazard implications from a water-rich eruption. Bulletin of Volcanology, 82, 29. https://doi.org/10.1007/s00445-020-1361-2

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

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Alka Tripathy-Lang, PhD

Alka Tripathy-Lang is a freelance science writer based in Chandler, Arizona, and holds a Ph.D. in geoscience.
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