The Science Behind 'Dirty Thunderstorms': How Volcanoes Create Their Own Lightning

When a volcano erupts, its billowing ash clouds can suddenly crackle with bright flashes of lightning — a rare natural phenomenon scientists call "volcanic lightning," or a "dirty thunderstorm." It can occur wherever a powerful volcano is active, but it is recorded most often in countries along the Pacific Ring of Fire.

Japan's Sakurajima volcano produces volcanic lightning almost every time it erupts, and more photographs of the phenomenon have been taken there than anywhere else in the world. Indonesia's Anak Krakatoa and Ruang volcanoes have both produced massive electrical storms during eruptions, and lightning that appeared amid the ash of Iceland's Eyjafjallajökull eruption in 2010 drew global attention. The Philippines' Taal volcano and Chile's Calbuco volcano have also produced the phenomenon.

Ordinary lightning forms when ice crystals inside storm clouds rub against each other, but volcanic lightning works differently. During an eruption, huge quantities of ash particles, rock fragments and gases are ejected at high speed, and these ash particles collide and rub against one another intensely in the air, building up electrical charges. When positive charges accumulate in one part of the ash cloud and negative charges in another, lightning flashes within the ash to balance the charge once it crosses a threshold.

The largest volcanic lightning event on record came from the 2022 eruption of the undersea Hunga Tonga volcano. At its peak, the eruption produced about 2,615 lightning flashes per minute — twice as fast as any previously recorded storm on Earth — and generated close to 200,000 flashes, totaling nearly 500,000 electrical discharges, within an 11-hour span. Over 3 days, more than 580,000 lightning discharges were recorded in total, entering the Guinness World Records. Unlike ordinary lightning, which forms in the lower atmosphere, these flashes appeared 20 to 30 kilometers above sea level and spread through the ash plume in giant rings up to 250 kilometers wide.