Lightning researcher Arthur Few says he had probably looked at the two images of the May 3, 2008, volcanic lightning storm dozens of times before he noticed it: weird green channels of lightning. The volcano was Chaiten in Chile, which produced a spectacular light show caught by photographer Carlos Gutierrez.

“Has anyone here seen green lightning before?,” Few asked reporters gathered to learn about his discovery on Monday at the meeting of the American Geophysical Union (AGU) in San Francisco. No one had, including me, which is why I was keen on getting Few to present his discovery and hypothesis about its cause to the media at the meeting (Full disclosure: in addition to writing for Discovery News, I freelance for AGU and helped them comb through the scientific program and find good stuff for press conferences).

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Few, a professor emeritus at Rice University, thinks that green lightning is not really that unusual, but is perhaps hidden inside of regular thunderstorms. But the gigantic column of ash that was launched by Chaiten wore its green lightning on its sleeve, and Few wants to know why.

“What else do we have in the atmosphere that’s green?,” Few asked. One is the northern lights, or aurora, which glow green, red and white when electrons rain down from space and excite oxygen atoms, he said. Above 100 kilometers, the aurora are green. Higher up they are red.

“My working hypothesis is that the green ones are actually streamers,” Few said. A streamer is a lightning bolt that is effectively “a positive channel being pulled to a negative charge” higher up in the ash cloud.

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The mess of white lightning in the Chaiten image is the negative charges being generated throughout the cloud raining down and curving into the bottom of the ash cloud. And there is the positive green channel, or streamer, reversing the flow.

So far Chaiten is the only volcano known to have been caught in the act of making green lightning, but there is no reason to believe other volcanoes aren’t doing it as well, Few said. Which means it’s up to all you volcano chasers out there, to find it again.

IMAGE: On the night of May 3, 2008, the erupting Chaiten Volcano in Chile created a fantastic lightning storm. Chaiten is located some 800 miles south of the capital Santiago. Its eruption caused the evacuation of thousands. Credit: UPI Photo/Landov