Magnetotelluric pulses generated by volcanic lightning at Sakurajima volcano, Japan

Abstract

Continuous magnetotelluric (MT) measurements were conducted at Sakurajima volcano, Japan, revealing syn‐eruption electric pulses (and sometimes accompanying geomagnetic pulses). Movies of the eruptions, recorded with timing provided by a GPS clock, show a large number of volcanic lightning flashes. Some MT pulses occurred simultaneously with lightning flashes. Pulses were observed more than 10 seconds after the onset of the eruption, and tend to occur during eruptions that emit volcanic ash to high altitudes. Pulses were more common during mild eruptions rather than during Vulcanian eruptions. The observations suggest that the dominant mechanism of volcanic lighting is similar to that of lightning in thunderstorms, in that it requires the collision of particles and subsequent separation of positive and negative charge.