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.
Ronald Thomas at New Mexico Institute of Mining and Technology in the US, and colleagues, used two receiving stations to monitor a series of short eruptions from the Mount St. Augustine volcano in Alaska, US, in January 2006. They detected a persistent “background” radiation emanating from the volcano’s vent which they believe is the product of nearly continuous sparking and miniature bolts of lightning tens of metres long.
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The low-energy lightning forms differently than thunderstorm-style lightning. Rather than neat layers, the force of material exploding from a volcano’s vent causes chaotic charge build up.
“When particles bang into each other, they exchange mass and electrons,” says Thomas “But the electrons don’t get distributed evenly, so a charge is formed.”
Steve McNutt, a team member at the University of Alaska, US, believes the work will prove useful as an added dimension of hazard assessment, especially in issuing advisories for planes, which can be severely damaged by flying through volcanic plumes. “We now know that we can detect the presence of a volcanic plume” at night and before it can be detected visually, he says.
Journal reference: Science (vol 315, p 1097)
