The most common type of lightning that researchers observed occurred shortly after the volcanic eruption and flashed high in the towering plume of ash and gas.
This lightning may be the product of dirty thunderstorm activity similar to that found in conventional thunderstorms.
The volcanic eruption itself is unable to generate sufficient electric charge to spark lightning for long after the eruption occurs or far from the crater, the researchers said.
Instead the scientists believe that electric charges are generated when rock fragments, ash, and ice particles in the plume collide to produce static charges—in much the same way that ice particles collide to create charge in regular thunderstorms.
"As the plume started going downwind, it seemed to have a life of its own and produced some 300 more or less normal [lightning bolts]," the University of Florida's Uman said.
"The implication is that it has produced more charge than it started with. Otherwise [the plume] couldn't continue to make lightning."
Volcanic eruptions release significant amounts of water, which may help fuel these dirty thunderstorms.
"Most of the volcano literature treats volcanic lightning as a different animal than natural cloud lightning," Uman said.
But, he noted, at least one kind of volcanic lightning appears to be "not all that much different than [conventional lightning in] a thunderstorm."
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