Picture gallery: the Chaiten volcano

The photo of lightning bursting out during a volcanic eruption in Chile, above, was a truly awesome sight. Although the picture seemed to show a thunderstorm colliding with the cloud of volcanic ash, it actually showed a marvellous phenomenon known as volcanic lightning.

Usually, lightning is sparked off by countless tiny pieces of ice inside a turbulent thundercloud banging into one another. Each collision generates static electricity, rather like a balloon rubbed on a jumper.

Eventually, the entire cloud turns into a colossal battery and the electricity is discharged as a gigantic spark – lightning.

A recent theory pictures the volcanic cloud as a “dirty thunderstorm”.

As fragments of rock and ash particles shoot upwards in the towering plume, they hit each other and the friction generates static charges that creates lightning bolts. And as the volcanic cloud cools off high up in the atmosphere, water from the eruption turns to ice and adds extra punch to the electrical storm.

Smaller lightning bolts also have been discovered bursting out from the mouth of a volcano’s crater as the gases and ash explode, but what generates this lightning is not known.

What is clear is that volcanic lightning is dangerous.