Probabilistic tephra fall hazard and risk assessment

A key goal of volcanology is accurate, quantitative forecasting of the potential hazard and risk associated with future volcanic events. Such assessments inform decision makers and enable emergency management plans and risk mitigation procedures, such as land-use planning and improved building codes, to be implemented prior to volcanic crises. This thesis is concerned with developing probabilistic methodologies to quantify tephra fall hazard and risk. Statistical analyses of eruption histories offer one of the best indications of future volcanic activity. Global databases of large magnitude (VEI ≥ 4) volcanic events were compiled and explored to derive general statistics describing explosive eruptive behaviour. A key finding was that volcanic events are commonly characterised by multiple explosive stages. To more accurately assess the tephra fall hazard applicable to such multi-stage eruption sequences, in comparison with more traditionally assessed single-stage events, a conditional hazard assessment model was developed for the Okataina Volcanic Centre in New Zealand, employing probabilistic simulation techniques and tephra dispersion modelling. Hazard and risk assessments are commonly volcano or location-specific; however, many communities are exposed to tephra fall hazard from multiple volcanic sources. To provide a relative assessment across a large area, a fully probabilistic assessment methodology was developed to assess the tephra fall hazard from 190 volcanoes in the Asia-Pacific region. Population density data were combined with tephra fall hazard estimates to determine a population-weighted hazard score. This methodology was further developed to incorporate population vulnerability and provide an estimate of the tephra fall risk to 18 major cities in the Region. This represents the first comprehensive view of tephra fall hazard and risk across the Asia-Pacific region. Assessment methodologies developed in this thesis utilise generic principles of hazard and risk assessment and may be applied to any other volcanic centre or region.