Lightning is phenomenon that is typically associated with thunderstorm clouds, yet is also generated during volcanic eruptions.

The first eyewitness account of a volcanic eruption came from Pliny in the 1st century AD, who describes volcanic lightning in addition to the eruption, that destroyed Pompeii. Although volcanic lightning has been witnessed and reported for centuries, our research program at LMU represents a comparitively recent research field. Our basic assumption is that lightning is not a random feature of eruptions, but a process directly linked to eruptive dynamics.

We study the phenomenon in our laboratory in the Theresienstraße: Particles of volcanic ash are accelerated into a shock tube and imaged with the aid of a high-speed camera. This allows us to observe the properties of the discharges that develop in the ash cloud. The next stage of the project involves field observations aimed at identifying the responsible parameters for generating the lightning. As part of a large-scale project supported by the European Research Council (ERC), we have developed a unique set of instruments which are capable of measuring and analysing flashes. We use them for example at the Cumbre Vieja volcanic chain, which provided an exceptional kick-off opportunity for our project.

Summary of our previous results

So far, we have demonstrated that both the number and the size of the volcanic ash particles influence the generation of lightning flashes: the smaller the particles, the higher the number of observed flashes.

During our observations, we repeatedly asked ourselves whether the overall magnitude of an eruption affects the generation of lightning. On La Palma, we had the chance to witness a comparitively small-scale explosive eruption which nevertheless produced a lot of volcanic lightning. This observation essentially confirms our basic assumption: practically all eruptions have an inherent tendency to generate lightning. This leads us to a rigorously testing and characterising our instrumentation.

Process of field work

In the event of an imminent outbreak, we organised that we can bring all our instruments to the site on the island and are in regular consultation with the local authorities and scientists. When we set up our instruments in the restricted zone, we began with the measurements. Although we had originally planned to take the instruments back to Munich at the end of the campaign, the cooperation with our local colleagues proved so effective that we decided to leave them in situ on the island. Since then, we have continued to work closely with the research team on site, who provide us with the data required for our ongoing analyses.

A further objective of our project is to enhance the capabilities of the instruments we have developed, with the goal of adding them into the standard portfolio of an integrated monitoring package. Their use during an active eruption offers an ideal setting to demonstrate their value and robustness in field conditions.