It’s called a Dirty Thunderstorm and a study in the journal Science explains that the electrical charges that cause the lightning are generated when rock fragments, ash, and ice particles in a volcanic plume collide and produce static charges, just as ice particles collide in regular thunderstorms. Only it’s more dramatic than regular lightning and far more difficult to capture for obvious reasons.
As the plume from a volcano starts going downwind, it takes on a life of its own and produces some 300 or so lightning bolts. Scientists aren’t exactly sure why this happens but think it’s safe to assume that the plume suddenly produces more charge than it started with, otherwise the it couldn’t continue to make lightning.
Anyway, regardless of what causes this brilliance, watch this video. It’s the coolest thing you’ve seen — maybe ever!