Infrasonic signals generated by volcanic eruptions

Volcanic eruptions are driven by excess pressure inside magma conduits, and thus volcanoes can be efficient radiators of acoustic signals. The amplitude and period of an infrasonic pulse generated by an eruption depend on the quantity and acceleration of ejected material. Strombolian and small Vulcanian explosion pulses resemble low-yield TNT blasts and may be observed at distances of tens of kilometers. Vigorous Vulcanian explosions may be observed at ranges of hundreds to thousands of kilometers. Plinian explosions may emit a destructive shock wave as well as generate gravity waves that circumnavigate the globe. Pelean eruptions excite infrasonic waves during the collapse, bursting, and avalanching of lava blocks and debris. In addition to these transient events, most volcanoes exhibit a type of vibration known as tremor, which consists of a sustained oscillation with dominant frequencies in the band of 1-10 Hz. These signals are traditionally attributed to the resonance of magma-gas mixtures inside volcanic conduits. Infrasonic signals generated during tremor, explosion, and pyroclastic flow episodes can be used to monitor an eruption sequence even under low-visibility conditions. Although it is possible to observe eruption pressure signals with individual sensors, infrasonic arrays are more desirable because they can filter out ambiguous signals. However, infrasonic array designs must reduce the detrimental effect of wind noise either through careful site selection or a suitable spatial filter design.