Dirty Thunderstorm, Volcanic Lightning Weather Phenomenon

A famous image of the phenomenon was photographed by Carlos Gutierrez and occurred in Chile above the Chaiten Volcano. It circulated widely on the internet. Other instances have been reported above Alaska's Mount Augustine volcano, and Iceland's Eyjafjallajökull volcano.
Causes
A study in the journal Science indicated that electrical charges 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.