]COVER PHOTOGRAPH: SERGIO TAPIRO VELASCO.
A powerful eruption illuminates the slopes of the Colima volcano in Mexico on December 13, 2015. Winning photograph of the 2017 National Geographic travel photography contest.[/caption] The appearance of lightning in volcanic eruptions is, according to the most general explanation, a meteorological phenomenon that forms when fragments of rock, ash, and ice particles expelled by the volcano collide with each other and cause electrical reactions. This phenomenon is known as a "dirty thunderstorm".
Although the ash coming out of the volcano is neutral, the temperature differences, friction, and collisions between particles and gases cause them to become electrically charged with opposite signs.
Having different densities, these particles move and progressively separate into positive and negative charges. When the potential difference is large enough, the discharge occurs.
In addition to this, some experts like Keri Nicoll, director of a research team from the universities of Bristol, Reading, and Bath (United Kingdom), believe that there is another very important agent in the formation of this lightning: radon.
Radon is a radioactive, colorless, and odorless gas that is naturally released in eruptions.
The origin of this gas is entirely natural and is related to the natural radioactive decay of uranium.
Nicoll's team examined the eruption of the Stromboli volcano in Sicily. There they observed that, although the generated clouds had hardly any ash, they were highly charged. After this analysis, the experts determined that the origin of this electrification could be radon.
According to these researchers, the presence of this gas, in addition to ionizing the air, is capable of increasing the charge and electrifying volcanic plumes. However, Nicoll, the research director, acknowledges that they still need to take more measurements. Even so, she states that there is no other known mechanism of electricity generation that can explain the group's observations. Therefore, the research is promising, and it is very likely that this is the true explanation for the so-called "dirty thunderstorms".
