For the first time in more than 42 years, the Calbuco volcano in southern Chile has erupted. Two blasts in 24 hours on April 22nd sent plumes of ash and volcanic gases shooting at least 33,000 feet high, well into the altitudes where planes fly. One of the eruptions occured at night and put on a spectacular display of volcanic lightning:
Researchers have long known that volcanic eruptions produce strong lightning. Findings published in a 2012 Eos article reveal that the largest volcanic storms can rival massive supercell thunderstorms in the American midwest. But why? Volcanic lightning is not well understood.
Lightning is nature's way of correcting an imbalance of electric charge. In ordinary thunderstorms, one part of a thundercloud becomes positively charged, and another part becomes negatively charged. This charge comes from collisions between particles: e.g., droplets of water and crystals of ice rub together, creating static electricity in much the same way as woolen socks rubbed against carpet. Lightning arcs between charge-separated regions.
Something similar must be happening inside volcanic plumes. One hypothesis holds that catapulting magma bubbles or volcanic ash are themselves electrically charged, and by their motion create charge-separated areas. Another possibility is that particles of volcanic ash collide with each other and become charged through triboelectric rubbing. In short, no one knows. It is a beautiful and terrifying mystery.