Dirty Thunderstorm, Volcanic Lightning Weather Phenomenon

A dirty thunderstorm (also, Volcanic lightning) is a weather phenomenon that occurs when lightning is produced in a volcanic plume.
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.