Search

Electrical discharges are observed in many volcanic eruptions and they have often been used as indicators of such eruptions. Volcanic lightning is remarkably similar to those produced during thunderstorms and is called analogous to thunderstorm-like plume lightning. The WWLLN developed a program called "Ash Cloud Monitor" (ACM), in which alerts are issued for possible volcanic eruptions when lightning strokes are detected around a volcano. The ACM tool has demonstrated to be a very effective technique to be aware of volcanic eruptions. However, most of the alerts released by ACM belong to false alarms of volcanic activity, because, in general, the detected lightning is produced by thunderstorms near the volcano. In order to assess and improve the ACM to detect volcanic eruptions, reducing false alert emissions and improving the quick interpretation of them, we develop a web platform called Georayos-VolcanoAr with a new structure and a modified algorithm, with respect to the algorithm used by ACM, for the classification of alerts. The new algorithm considers an alert system with 3 levels: Red - Yellow - Green, with the Red alert being the highest level and decreasing towards Green. The Red alert was assigned to those volcanoes where only recorded lightning within a radius of 20 km or the lightning detected within a radius of 20 km is at least twice as much as that detected up to 100 km from the vent. The study focused on 32 volcanoes located in the Andes, close to the Argentine-Chilean border, and analyzed the results reported by the ACM network in terms of a climatological study of the lightning activity, thunderstorm days and predominant winds in that region. This analysis serves as a basis for a general recognition of the study zone in order to improve the interpretation of the distribution and generation of false alerts; as well as to help decision makers, among others, to have a reference that allows them to issue the warning. • The electric discharges detection tool to detect volcanic events is more precise towards the Southern sector of the study area. • Georayos-VolcanoAr is a web platform that improves the alerts received by the decision maker for their quick interpretation. • We observed a decrease in the number of false alerts issued compared to the Ash Cloud Monitor. • Georayos-VolcanoAr helps to discriminates between meteorological and volcanic lightning with greater precision. [ABSTRACT FROM AUTHOR]

Sakurajima volcano in Japan is known for frequent eruptions containing prolific volcanic lightning. Previous studies from eruptions at Redoubt have shown preliminary correlations between seismic, infrasound, and radio frequency signals. This study uses field data collected at Sakurajima from 28 May–7 June 2015 and multivariable statistical modeling to quantify these relationships. We build regression equations to examine each of the following parameters of electrical activity: (1) the presence of electrical activity, (2) the presence of the radio frequency signal called continual radio frequency impulses (CRF), (3) the presence of lightning, (4) the overall duration of electrical activity, and (5) the total number of radio frequency sources located by a lightning mapping array. We model these response variables against: (1) seismic energy, (2) infrasound energy, (3) seismic duration, (4) infrasound duration, and (5) the volcano acoustic seismic ratio. Our final regression equations show that each parameter of electrical activity is best defined by a separate set of response parameters, but overall events with greater explosivity correlate with higher amounts of electrical activity. Specifically, (1) the probability of CRF occurring, and the overall number of located radio frequency sources are likely related to deeper fragmentation depths; (2) the probability of electrical activity occurring at all, and specifically the probability of lightning being generated are correlated with high infrasound energies indicating that the gas thrust phase of plume formation plays an important role in charge generation; and (3) the longer an eruption (as determined by the duration of the infrasound signal) the longer we can expect to see radio frequency signals generated. • Overall volcanic electrical activity is correlated with high infrasound energies • Continual radio frequency impulses, produced at the vent, accompany magmatic fragmentation • Volcanic lightning generation is influenced by plume dynamics [ABSTRACT FROM AUTHOR]

The paper is devoted to the description of observations over atmospheric and electric effects from volcanic eruptions on Kamchatka peninsula (Russia) and perspectives of their development. To collect information about atmospheric-electric effects accompanying the eruptions of Kamchatka volcanoes, three sensor networks and a VLF radio direction finding station are used. The World Wide Lightning Location Network (WWLLN) provides information on high-current lightning discharges that occur during the development of an eruptive cloud (EC). Variations in the electric field of the atmosphere (AEF E z ), during the passage of EC, were obtained by a network of electric field mills at the sites for volcanic activity observations. Seismic detector network was used to make precision reference to the eruptions. Based on the data obtained, a description is given of the dynamics of eruptions of the most active volcanoes in Kamchatka and the Northern Kuril Islands (Shiveluch, Bezymianny, Ebeko). The paper presents a simulation of the response of the atmospheric electric field, which showed that the approximation by the field of distributed charges makes it possible to estimate the volume charges of EC. The fact of a multi-stage volcanic thunderstorm is confirmed. The first stage is associated with the formation of an eruptive column, and the second with the emergence, development and transfer of EC. Registration of electrical and electromagnetic processes in eruptive clouds can be one of the components of complex observations of volcanic eruptions in order to assess the ash hazard for air transport. [ABSTRACT FROM AUTHOR]

Lightning-induced textures in volcanic ashfall deposits can take several forms, including lightning-induced volcanic spherules (LIVS), spherule aggregates, and pumiceous particles. Here, two newly identified textures are described in the products of current impulse experiments conducted on ash samples spanning a range of bulk compositions from basic (49 wt% SiO 2) to intermediate (53–58 wt% SiO 2) to acidic (72–76 wt% SiO 2), at peak currents of 7 kA, 25 kA, and 100 kA. Due to the location of subjected samples on a solid, flat surface in the experimental apparatus, both hair-like particles (1–10 μm in diameter) and plate-like particles (>100 μm in diameter) are produced. These textures result from not only the high temperatures generated by the discharge (>1500 °C), but also by the expansion of a shock front with a radius twice the size of the discharge channel. The pressure behind this shock front ranges from 0.41 MPa for the 7 kA impulse currents to 0.77 MPa for the 100 kA impulse currents and the velocity of the shock ranges from 617 m/s to 846 m/s. The combined high temperatures and shock wave expansion simultaneously melts the volcanic ash particles, fuses them together, and stretches them out, which alters the very small (<32 μm) angular grains into larger hair-like and plate-like shapes. Although LIVS, spherule aggregates, and pumiceous particles have been documented in ashfall samples from explosive volcanic eruptions, these newly identified hair-like and plate-like textures have not. The existence of hair-like and plate-like particles in volcanic ashfall samples expands the variability of lightning evidence and may indicate the occurrence of cloud-to-ground lightning discharges during explosive eruptions. • Lightning-induced textures in volcanic ash include plate-like and hair-like particles. • Current impulse experiments permit calculation of shock velocities and pressures. • The shock front expands faster than the speed of sound, elongating melted ash aggregates. [ABSTRACT FROM AUTHOR]

Volcanic ash produced during explosive eruptions may serve as ice nuclei in the atmosphere, contributing to the occurrence of volcanic lightning due to tribocharging from ice–ice or ice–ash collisions. Here, different ash samples were tested using deposition-mode and immersion-mode ice nucleation experiments. Results show that bulk composition and mineral abundance have no measurable effect on depositional freezing at the temperatures tested, as all samples have similar ice saturation ratios. In the immersion mode, there is a strong positive correlation between K2O content and ice nucleation site density at −25 °C and a strong negative correlation between MnO and TiO2 content at temperatures from −35 to −30 °C. The most efficient sample in the immersion mode has the highest surface area, smallest average grain size, highest K2O content, and lowest MnO content. These results indicate that although ash abundance—which creates more available surface area for nucleation—has a significant effect on immersion-mode freezing, composition may also contribute. Consequently, highly explosive eruptions of compositionally evolved magmas create the necessary parameters to promote ice nucleation on grain surfaces, which permits tribocharging due to ice–ice or ice–ash collisions, and contribute to the frequent occurrence of volcanic lightning within the eruptive column and plume during these events. [ABSTRACT FROM AUTHOR]