photos of sakurajima, the most active volcano in japan, by takehito miyatake and martin rietze. volcanic storms can rival the intensity of massive supercell thunderstorms, but the source of the charge responsible for this phenomenon remains hotly debated.

in the kind of storm clouds that generate conventional lightning, ice particles and soft hail collide, building up positive and negative charges, respectively. they separate into layers, and the charge builds up until the electric field is high enough to trigger lightning.

but the specific mechanism by which particles of differing charges are separated in the ash cloud is still unknown. lightning has been observed between the eruption plume and the volcano right at the start of an eruption, suggesting that there are processes that occur inside the volcano to lead to charge separation.