Assessing the strength of volcanic eruptions using acoustic infrasound measurements

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During volcanic eruptions, fragments of rock are ejected from volcanoes at high speed, and driven into the atmosphere by hot gases. This abrasive mixture of fine particles, called volcanic ash, is created when expanding gases push magma through the volcanic conduit and towards the surface. The sudden drop in pressure as gas-charged magma approaches the Earth's surface results in violent explosions that shatter magma. Small fragments of liquid are forced into the atmosphere where they rapidly solidify, forming the dramatic plumes frequently observed above erupting volcanoes. These mixtures of gases and fine rock fragments can rise to heights of several kilometers where atmospheric winds transport volcanic ash over large horizontal distances. It is common knowledge that airborne volcanic ash represents a direct threat to aviation. The growing problem of aircraft encounters with ash clouds has been recognized for some time. The volume of erupted material, the rate at which it is ejected from volcanic vents, and the maximum height of eruption plumes are key inputs into numerical models of atmospheric ash dispersal. Recent studies have highlighted the potential of acoustic measurements in the infrasonic band for assessment of eruption source parameters. Erupting volcanoes perturb the atmosphere by emission of large amounts of material. These emissions produce sound waves in the infrasonic band, below the threshold of human hearing. The intensity of the produced infrasound can, thus, be linked to the volumetric acceleration of the atmosphere, and the rates and amount of material ejected at the vent. The use of oversimplified models of volcano acoustic sources and infrasound propagation has, however, partly hindered more extensive application of methods based on the use of acoustic data to assess the strength of eruptions. This project will overcome past limitations by implementing the first theoretical and numerical framework for modelling and inversion of acoustic infrasound signals, and assessment of eruption source parameters in real-time. We will build complex numerical models of acoustic wave propagation that take into account atmospheric variability and the effects of topography. Observed and theoretical signals will be compared in order to assess eruption parameters such as the strength and mechanisms of volcano acoustic sources. Further, we will show how these parameters can be used as input into numerical models to dramatically improve predictions of atmospheric propagation of volcanic ash plumes. We will use multi-disciplinary data collected during a field campaign at Mt. Etna, Italy, to confirm our predictions and calibrate our models. This project addresses important questions in volcanology and will contribute to our understanding of infrasound signals, volcanic emissions, and eruption dynamics. This will, in turn, improve monitoring and detection of volcanic hazards. The feasibility of using infrasound as a continuous, remote, tool to detect and characterise volcanic emissions will be scrupulously evaluated. We anticipate that our research will influence the development of new strategies to monitor and forecast volcanic ash hazards in real-time.