Vulcanian eruptions at Sakurajima Volcano: geophysical data, numerical modelling, and petrological evidence

We investigated the magma conduit system beneath three active craters that have repeatedly generated Vulcanian eruptions at Sakurajima Volcano, Japan, by analysing seismic, infrasound, and tilt data. The hypocentres of the earthquakes associated with the Vulcanian eruptions are distributed separately at shallow depths of approximately 0.5 km beneath the craters. Infrasound indicated that the swelling of the crater floor starts approximately 0.2 s after the occurrence of earthquakes and that the eruption starts about 0.3 to 0.5 s later. During an eruption, tilt vectors at a station approximately 2.7 km far from the active craters indicated a deflationary trend directed toward one of the three active craters. A 1-D conduit flow simulation indicated pressure build-up at a depth of 0.4–1.0 km beneath the crater, consistent with previously reported pressure sources during eruptions detected by geodesy. Volcanic lapilli emitted from the three craters have the same chemical composition; hence, Vulcanian eruptions of all three studied craters originate from a common magma source.