Why Do Volcanoes Produce Lightning?

Volcanic lightning ("dirty thunderstorms") occurs during explosive eruptions when billions of ash particles, rock fragments, and ice crystals collide at high speed within the eruption column. These collisions transfer electrons between particles (triboelectric charging), creating regions of opposite charge — similar to how ice crystals generate charge in normal thunderstorms. When the voltage difference between charged regions grows large enough, it discharges as lightning. Volcanic lightning has been observed in eruptions worldwide: the 2010 Eyjafjallajokull eruption in Iceland, the 2015 Calbuco eruption in Chile, and the ongoing eruptions at Sakurajima in Japan all produced spectacular displays. Studies using lightning mapping arrays have shown that volcanic lightning occurs in multiple zones: near the vent (where colliding rock fragments create charge) and high in the plume (where ice-coated ash particles behave like thundercloud ice crystals).