This cool picture depicts a lightning storm that takes place in the middle of a volcanic eruption. Scientists aren’t 100% sure why this happens, but the primary theory goes that when a volcano erupts, it projects positively-charged debris into the atmosphere. These charges then react with negative charges already present, which results in a bolt of lightning.
Since 2007, a small handful of studies have led to the conclusion that there exist at least two types of volcanic lightning – one that occurs at the mouth of an erupting volcano, and a second that dances around in the heights of a towering plume. Findings published in a 2012 article in the geophysics journal Eos reveal that the largest volcanic storms can rival the intensity of massive supercell thunderstorms common to the American midwest. Still, the source of the charge responsible for this humbling phenomenon remains hotly debated.
One hypothesis, floated by Thomas' team in 2007, suggests that magma, rock and volcanic ash, jettisoned during an eruption, are themselves electrically charged by some previous, unknown process, generating flashes of electricity near the volcano's opening. Another holds that highly energized air and gas, upon colliding with cooler particles in the atmosphere, generate branched lightning high above the volcano's peak. Other hypotheses, still, implicate rising water and ice-coated ash particles.
"What is mostly agreed upon," writes geologist Brentwood Higman at Geology.com, "is that the process starts when particles separate, either after a collision or when a larger particle breaks in two. Then some difference in the aerodynamics of these particles causes the positively charged particles to be systematically separated from the negatively charged particles."
The exciting thing about this process is that these differences in aerodynamics, combined with various potential sources of charge (magma, volcanic ash, etc) suggest that there may actually be types of volcanic lightning we've yet to observe.