What Causes Volcanic Lightning?

 

    On March 10, 2010, Eyjafjallajökull volcano, a caldera in Iceland covered by an ice cap, erupted. It sent plumes of clouds across most of Europe and the Atlantic Ocean. Photos of the eruption show lightning originating and ending in the cloud of ash that hovered over the volcanic opening.

   The largest volcanic storms are similar to supercell thunderstorms that spread across the American Midwest. But while those thunderstorms are fairly well understood, volcanic lightning still remains mysterious. The remote location of volcanoes and infrequent eruptions make volcanic lightning difficult to study. In general, lightning occurs through the separation of positively and negatively charged particles. Differences in the aerodynamics of the particles separate the positive and negative. When the difference in charge is great, electrons flow between the positive and negative regions. A lightning bolt is a natural way of correcting the charge distribution.

   So what makes volcanic lightning so difficult to understand? Scientists believe ejections from the volcano into the atmosphere carry a large electrical charge, but they aren’t sure if it originates in the volcano or occurs afterward. Very high  frequency radio emissions and other types of electromagnetic waves now allow scientists to observe the lightning inside the ash plume. Since 2006, scientists have used the new technology during three separate eruptions, including Eyjafjallajökull, and can distinguish two phases for volcanic lightning. The first phase, called the eruptive phase, is the intense lightning immediately after the eruption near the crater. Presumably, charged particles from the volcano are the source of this lightning that occurs near the crater. Phase two, called the plume phase, is lightning that forms inside the ash plume downwind of the crater. The origins of this lightning remain a mystery.

    In the 2010 eruption of Eyjafjallajökull, plumes of smoke significantly interrupted airline traffic, resulting in billions of dollars of lost revenue. The more we understand about volcanoes, the better we get at predicting an eruption and the potential consequences. Some scientists hope that studies of the composition of  gases inside a volcanic plume could tell us more about the early stages of our planet and the conditions that created the building blocks of life, making volcanic lightning a worthy pursuit. At a safe distance, of course.