Measurements of electric charge distribution in volcanic plumes at Sakurajima Volcano, Japan

Abstract

Measurements of perturbations in the atmospheric potential gradient around volcanic plumes at multiple (from two to five) sites, and measurements of the charge-mass ratio of ash particles falling from volcanic plumes, were carried out at Sakurajima Volcano, Japan. Results from 28 and 29 October 1995, show that the nature of the perturbations depends on the intensity of plume activity. Although plume activity was vigorous on 28 October, negative perturbations were predominant. As plume activity peaked, the magnitude of negative perturbations decreased just below the plume and increased at an off-axis site. During the peak period, positively charged ash particles fell out from the plume. This suggests that the active plume dominantly contained negatively charged materials, and that positively and negatively charged materials were added to the lower and upper parts of the plume, respectively, during the peak period. On the other hand, as plume activity became less vigorous on 29 October, the perturbations were characterized by a positive anomaly followed by a negative anomaly. Because wind velocity increased with altitude that day, we infer that positive and negative charges were distributed in the upper and lower parts of the plume, respectively. The differences in perturbations observed on 28 and 29 October suggest that volcanic plumes are generally composed of three parts: an upper part with positively charged gas and aerosol, a middle part with negatively charged fine ash particles, and a lower part with positively charged coarse ash particles. The compilation of present and previous results from Sakurajima and other volcanoes indicates that the effect of the negative charge in the middle part was predominant in most cases, although positive perturbations caused by the upper part were observed around some weak plumes. The effect of positively charged particles in the lower part was observable only when plume activity was sufficiently strong because positively charged coarse particles tended to fall out near the vent.

Triboelectrification: A review of experimental and mechanistic modeling approaches with a special focus on pharmaceutical powders

“…Presence of multiple size fractions can trigger inter-particle charge transfer in identical materials, and the magnitude of charge has been reported to increase with the concomitant increase in particle size ranges 86,87 . Bipolar charging in identical materials has been perceived in multiple fields including pharmaceutical unit operations such as fluidized bed drying 88 and pneumatic conveying 89 , dust storms [90][91][92][93] , volcanic plumes 94 and aerosols such as found in DPIs 95 . Although most reports suggested this phenomenon resulting in the larger particle fractions to acquire positive charges and smaller particles charging negatively, a contradictory pattern have also been observed at times 88 .…”

Multiparametric observation of volcanic lightning: Sakurajima Volcano, Japan

“…Organization of charges may generally be observed at a later stage during the evolution of the plume when fine particles, which tend to be transported higher up by the convection of hot gases, are separated from the coarser particles thereby generating a dipole or a tripole [Miura et al, 2002]. At Sakurajima this process is achieved at times of seconds to minutes after the inception of the explosion [Aizawa et al, 2010].…”

“…To date, volcanic lightning has been mainly detected via electric field changes [Anderson et al, 1965;James et al, 1998;Miura et al, 2002] and via radio frequency radiation generated by the plume electrical activity [Bennett et al, 2010;Thomas et al, 2010;Behnke et al, 2013]. Thus, volcanic lightning may provide a valuable monitoring tool for active volcanoes, allowing detection of ash emissions from safe distance and in inclement weather conditions [Behnke and McNutt, 2014].…”

Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

“…A number of techniques have been used to study the electrical activity of volcanic plumes including close-range VHF lightning mapping arrays (e.g., Thomas et al 2007;Behnke et al 2013), long-range VLF lightning observations (e.g., Bennett et al 2010) and optical lightning detection using high-speed cameras (Cimarelli et al 2015). Direct measurement of the electric field near the vent, where the electrical activity in the volcanic plume is first observed, is difficult, but a handful of studies exist including those by Anderson et al (1965), Gilbert et al (1991), James et al (1998), Miura et al (2002). Laboratory-based experiments are also essential to studying volcanic charge generation mechanisms in a controlled environment and can allow different charge mechanisms to be examined individually.…”