Assessing the strength of volcanic eruptions using acoustic infrasound measurements

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.

The impact of this study is closely linked to:
1.Providing a new and improved workflow for the interpretation of volcano infrasound data
2.Providing estimates of eruption source parameters for testing and validation of numerical models of atmospheric ash dispersal
3.Improving monitoring of eruption related phenomena by characterising their intensity and temporal evolution
4.Providing a real-time, continuous, monitoring system for volcanic eruptions
The benefits will be a better understanding of the eruption process and improved accuracy in short-term forecasts of volcanic ash dispersal. The study will engage with non-academic beneficiaries such as research and monitoring institutes. For them prompt assessment of eruption strength is crucial. Two organisations are project partners: the University of Alaska, part of the Alaska Volcano Observatory (AVO), and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) of Catania. AVO is responsible for monitoring more than 50 active volcanoes along the Aleutian Arc of Alaska, in addition to other volcanoes in Kamchatka and the Mariana Islands. INGV Catania is responsible for the surveillance of Mt. Etna in Italy. Working with these organisations means that the outputs of our study will be immediately tested, integrated into day-to-day assessment of volcanic unrest, and channeled more efficiently to similar beneficiaries. Volcano monitoring agencies communicate directly with civil protection and other government authorities to help communities prepare for, or respond to, hazards. The tools developed in this study will allow development of evidence-based policies and procedures, and thus, boost societal impact.
Organizations such as the Volcanic Ash and Aviation Centres (VAAC), whose purpose is to track ash clouds from eruptions, are among other potential beneficiaries. VAAC's employ specialist forecasters that use satellite data to constrain ash dispersion models. Satellite data are often not available in the early hours of eruptions. Rapid and reliable estimates of mass eruption rates and plume height from more readily available observations will improve the response of these organisations in the event of volcanic eruptions.
Volcanic eruptions are among a number of poorly constrained, non-modeled, perils. Third party stakeholders such as insurers need further understanding of how these events can affect their portfolios. Volcanic hazards can potentially trigger significant losses. Improved ash dispersion modelling resulting from better constrained parameters will allow a reliable assessment of the potential impact of eruptions on aviation and infrastructure.
In terms of academic impact the project will outline new methods of investigating the propagation and generation of volcanic infrasound. The characteristics of acoustic sources, including strength and location, are directly linked to magmatic conditions within the conduit. This information is key to understanding the evolution and magnitude of eruptions.
To maximise impact we will attend relevant sessions in scientific conferences and workshops that produce guidelines for interpreting geophysical data, and communicating results to civil defence organisations. We will make software freely available to apply our inversion/modeling workflow in operational environments, and organize an end-of-project workshop during to train end-users in its use along with other relevant state-of-the-art infrasound monitoring methods. The study will contribute to to raise awareness among the general public, especially those living in areas affected by volcanic eruptions. Public engagement will be sought by designing an interactive website linked to this project, which will present our work and results in an accessible language, and engage the users.