Why does lightning often happen above volcanoes?

Volcanic lightning is one of nature's most spectacular sights and now researchers are discovering more about why it happens.

When a volcano erupts it creates a plume of hot volcanic ash, gas, rock and water vapour that is tightly packed together.

As it falls, tiny particles gain friction - some picking up a positive charge and others a negative charge - with lightning strikes taking place when a huge electrical spark flows between the two.

But now physicists think they understand more about how these different charges come about.

Scientists had wondered how a volcanic plume could pick up a charge, as particles of these kinds of materials wouldn't typically do this.

Now a study has shown that it's due to a fine layer of carbon covering the molecules, this allows the charge to be transferred when collisions take place.

The heat and upward-moving current of gas in a volcanic plume create conditions that are good for this.

The new research has been published by the Institute of Science and Technology Austria in the science journal Nature.