Why do volcanic eruptions sometimes create lightning in the ash cloud?

Volcanic lightning happens when ash, ice, and tiny rock fragments collide inside an eruption plume and separate electrical charges. As the plume rises and cools, charge differences can become strong enough to produce lightning flashes. This can occur even without ordinary thunderstorm clouds because the ash cloud itself becomes electrically active. Large eruptions such as Eyjafjallajökull in 2010 and the 2010 Mount Merapi eruption were associated with vivid volcanic lightning. Scientists study it because it helps track the plume’s movement and intensity.