Monday, April 18, 2016

Mystery of Volcano Lightning Explained

[Discovery News] When Mt. Vesuvius erupted in the year 79, famously burying the town of Pompeii in ash, historian Pliny the Younger recorded that the volcano expelled “frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame.” It was the first description of a phenomenon that, almost 2,000 years later, is the stuff of viral Internet photos: lightning that arcs its way through the ash plumes of some volcanic eruptions.
It’s a phenomenon that has, however, puzzled scientists, who have wondered exactly how such lightning is generated. Two new papers, published in Geophysical Research Letters, the journal of the American Geophysical Union (AGU), have helped provide clarity and, in the process, unify two competing schools of thought. (Yes, there are competing schools of thought on volcanic lightning.)
The basics of lightning are understood well enough: Particles within a cloud become electrified, generating a field in which positive and negative charges are separated, and the lightning restores the charges to balance. In thunderstorms, ice crystals are the particles that are electrified. What was unknown was whether ice was also required for volcanic lightning, or whether friction between particles of ash performed that role. The new studies show that both can be true, depending on the situation. Read More