How do lightning and volcanic ash clouds create dangerous storms near eruptions?

Inside a rising ash cloud, particles collide and rub against one another, which can separate electric charges. When enough charge builds up, lightning flashes through the plume, sometimes in spectacular bursts above explosive eruptions. This happens most dramatically in tall, dense ash columns such as those produced by Eyjafjallajökull in 2010 or Sakurajima in Japan. Volcanic lightning does not create the eruption, but it is a striking sign of an ash-rich explosive event. The combination of ash, lightning, and turbulence makes eruption clouds dangerous to aircraft and people nearby.