Characterizing Explosive Eruptions at Sakurajima Volcano, Japan, Using Seismic, Infrasound, Lightning and Video Data

The ability to determine volcanic ash plume characteristics from seismic and/or infrasonic records would enable increased accuracy in volcanic monitoring during times of low visibility. During May-June 2015 a field deployment of 6 infrasound sensors, 2 seismometers, multiple cameras, and 10 Lightning Mapping Array (LMA) stations were deployed around Sakurajima Volcano in Japan. During one month of observations (13 May to 10 June) hundreds of explosive eruptions were observed with plume heights reaching 4.3 km above the vent. The plumes varied in duration, ash content, and physical form. The resulting explosions exhibited a variety of infrasound waveforms including the classic long-period N shape as well as events with a mixture of high and low frequencies. For a subset of larger events, peak pressures ranged from 16 to 741 Pa at a distance of 3.6 km from the vent. The seismic signals are long period and emergent with no clear P or S-waves, although high frequency ground-coupled airwaves are visible in conjunction with the infrasonic record of some of the explosive eruptions. Peak ground displacements on the vertical component ranged from 2.1 to 183 um for the same subset of events. Volcanic lightning was both visually observed and recorded on the LMA stations. One of the goals of this project to determine if there are intrinsic relationships between ash plume characteristics, such as initial velocity or acceleration, ash grain size, texture, and composition, seismic and infrasound waveforms, and the presence and type of volcanic lightning. The rich variety of observations provides a good opportunity to determine such relationships