A new kind of low-energy lightning has been discovered, crackling and sparking in the mouth of an erupting volcano.

Traditional, thunderstorm-style lightning has long been associated with volcanic eruptions. As large plumes of ash and rock rise into the air, oppositely charged particles separate into layers. These layers build until the difference between them is great enough that a connection forms, releasing energy in a flash of electricity.

But in a new study researchers have shown conclusively that a new form of low-energy lightning is also active during eruptions, arcing between particles as they exit the volcanic vent at around 100 metres per second.