Electric Discharge in Erupting Mud

Self-ignition during the explosive eruption of mud volcanoes can create flames that in some cases reach heights that exceed hundreds of meters. To study the controls on electrical discharge in natural mud, we performed laboratory experiments using a shock-tube apparatus to simulate explosive eruptions of mud. We vary the water content of the mud and proportions of fine particles. We measure electric discharge within a Faraday cage and we use a high-speed video camera to image the eruption of mud and some of the electric discharge events. We find that (a) decreasing the proportion of fine particles and (b) increasing water content each suppress the number and magnitude of electric discharge events. Experimentally observed mud volcano lightning occurs where particles exit from the vent and within the jet of erupting particles.