Volcanic impact and risk assessment underpins effective volcanic risk management and volcanic risk reduction. Growing urbanisation and development in active volcanic regions therefore necessitates robust, applicable volcanic impact and risk assessment. Volcanic risk is driven by the interaction between the complex, multi-hazard, multi-phase volcanic system, and the equally complex societal systems exposed. These dynamic volcanic risk drivers are generally well-understood, or at least can be well-identified, but they have proven hard to quantify and incorporate into volcanic impact and risk assessment frameworks. Volcanic multi-hazards can cause a variety of impacts to critical infrastructure networks, which underpin the everyday operations and well-being of society. These impacts range from highly damaging to mildly disruptive, and have the potential to provoke widespread systemic impact to infrastructure networks far beyond the hazard extent. Current methods for volcanic impact assessment are limited by their generally single-phase, single-hazard perspective. They are further limited by their static, one-dimensional incorporation of exposure and vulnerability, despite recognition of the dynamic properties of these risk drivers. A more holistic approach is required to begin to investigate the interaction of the complex volcanic and complex infrastructure systems. Complex multi-scale challenges of this nature are increasingly being addressed by bringing scientists and practitioners together to collaborate in the production of disaster risk reduction (DRR) knowledge and disaster risk management (DRM) strategies. Volcanic impact assessments can serve as effective ‘boundary objects’, which help facilitate this collaboration between science, policy and practice.

This thesis presents a dynamic impact assessment framework for multi-hazard, multi-phase volcanic eruptions, through the lens of systemic risk to critical infrastructure networks. In order to develop this framework, the need was identified for 1) the development of a modular framework for multi- phase, multi-hazard volcanic eruption scenarios and 2) a methodology for the quantification of systemic vulnerability of critical infrastructure networks. The frameworks and tools developed were applied to the Taranaki region of Aotearoa-New Zealand, where Taranaki Maunga volcano is surrounded by distributed infrastructure networks of regional and national importance. This thesis presents a multi-phase, multi-hazard volcanic eruption scenario suite for Taranaki Maunga that is scientifically credible, meets stakeholder needs, and is representative of the range of possible hazard outcomes of the next eruptive episode. This thesis also quantifies the systemic vulnerability of distributed infrastructure in the Taranaki region, identifies areas or assets of high systemic vulnerability, and presents a tool for the rapid determination of network disruption under different volcanic regimes. Finally, this thesis presents a suite of dynamic volcanic multi-hazard impact scenarios for Taranaki Maunga that allow for the testing of mitigative strategies through the inclusion of risk management actions as modules in the framework. This thesis demonstrates the efficacy of co- creative volcanic risk research, and shows that the timing of risk management decisions under volcanic uncertainty is an important driver of volcanic risk. This work was undertaken in close partnership with local stakeholders, predominantly emergency managers and lifelines managers, who were collaborators and active participants at each step of the research timeline, ensuring the relevance and usability of the research conducted.

The findings of this thesis are framed and informed by global best-practice regarding DRR and DRM, including the strong inclusion of local stakeholder knowledge. The approaches and frameworks presented here have implications for enhancing volcanic risk reduction and management globally. They also provide a valuable resource for planning for and responding to an eruption of Taranaki Maunga. This body of work allows the assessment and characterisation of volcanic risk in the Taranaki region of Aotearoa-New Zealand. This work also enhances the ongoing collaboration between scientists and practitioners to assess, reduce and manage volcanic risk. This thesis has addressed the identified need for an initial investigation into the dynamic properties of volcanic multi-hazard risk and the drivers of volcanic and systemic risk during multi-phase volcanism.