Generation and propagation of infrasonic airwaves from volcanic explosions

Analysis of infrasonic pressure waves generated by active volcanoes is essential to the understanding of volcanic explosion dynamics. Unlike seismic waves propagating in the earth, infrasonic airwaves offer a relatively unfiltered representation of source motions at the vent during an eruption. Time-varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances (< 5 km from the vent). Thus the recorded excess pressure time series directly reflects the impulsivity of the degassing source at the vent. In the most simple experiments, infrasound monitoring is valuable for differentiation of subsurface seismicity from the seismicity associated with an eruption. In other instances, infrasound monitoring may be used in conjunction with seismic monitoring to understand the style of eruption and information about the physical source processes and source location. This manuscript is an introductory overview of the generation and propagation of volcanic infrasound. An analysis of infrasonic records generated from five volcanic case studies is provided in an accompanying article [Johnson et al., J. Volcanol. Geotherm. Res., in press].