FAQs:

• Volcano infrasound is defined as low frequency sound, generally considered less than 20 Hz, produced by volcanic eruptions or processes.
• The sources of volcano infrasound are aerial or in the shallow subsurface, as there needs to be a path between the source and the atmosphere.
• Volcanoes produce a wide variety of infrasound signals, including some of the loudest sounds ever recorded. These may include eruptions, vigorous degassing, and surficial mass movements (e.g. debris flows, avalanches, and lahars).
• Infrasound can be recorded at a variety of distances, including local (<15 km), regional (~15-250 km), and global (>250 km). Global distance infrasound recordings are possible due to (at times) favorable long-range infrasound propagation and low attenuation rates.
• Infrasound is a regular tool for volcano monitoring and research. It provides a means to detect, locate, and characterize eruptions, and in some cases can be used as a forecasting tool. Infrasound data are often combined with other datasets, such as seismic and remote sensing, to help better characterize the source.
• Specialized low frequency microphones, or microbarometers, are used to record infrasound. They are often deployed as a group of sensors in a systematic configuration, termed an array or network, to detect, characterize, and locate acoustic waves.

Examples of the variety of infrasound signals produced by volcanoes. Figure from Fee and Matoza [2013].