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Acoustic methods in geophysics

Many environmental processes generate sound, including the audible frequencies associated with some earthquake activity and with explosive volcanic eruptions. Volcanoes possessing steep-walled craters have been likened to ‘giant musical instruments’, and analysis of their changing acoustic emissions, especially as the dimensions of the crater change, may provide aids to the prediction of eruptions (Johnson et al. 2018). Indeed, acoustic methods have proven useful in making inferences about the mechanics of volcano behaviour more generally, including that of Whakaare / White Island, New Zealand (Walsh et al. 2019), which erupted on 9 December 2019 with the loss of 22 lives. The goal of this paper is to provide a brief history of the geophysical application of acoustic methods, from beginnings in the 19th century, to contemporary developments.