WHAT: Electromagnetic discharges that ignite during eruptions and inside ash plumes.
WHERE: Any big, explosive eruption ejecting massive ash clouds, such as Eyjafjallajökull in Iceland or Chaitén in Chile.
HOW: As magma breaks apart, it becomes charged, creating vent lightning that strikes out around the volcano’s mouth. Plume lightning can form as far as several hundred miles from the volcano, as erupted ash, rock, and gas interact with moisture in clouds to create bolts up to 20 miles long.
SUPERFREAKS: When Alaska’s Mount Redoubt erupted in 2009, more than 30 explosions over a two-month period generated more than 7,000 lightning flashes, with plume-lightning storms traveling 60 miles from the rim. Scientists measured 20 sessions of vent lightning as the eruption continued for two weeks. Bolts could be seen 80 miles across Cook Inlet from the town of Kenai.
THE FORECAST: No change. According to Ronald Thomas, a professor of electrical engineering at New Mexico Tech, incidences of lightning don’t increase over time.