Stewart C, Smid E, Charlton D, Leonard GS, Tomašek I, Wilson TM, Talbot N. 2019. Preparing for a sustained volcanic degassing episode in Auckland. Lower Hutt (NZ): GNS Science. 41 p. (GNS Science report; 2019/58). doi:10.21420/4NKW-TR68.
The Auckland metropolitan area is built upon the intraplate Auckland Volcanic Field (AVF), which poses a considerable threat to the highly exposed people and infrastructure of Auckland. An important component of evaluating and quantifying volcanic risks to Auckland has been the development of AVF eruption scenarios. These are useful for purposes such as assessing impacts on buildings and critical infrastructure and providing decision support for emergency managers and civil authorities. However, while several scenario-based studies have noted the potential for volcanic gas emissions to cause impacts on downwind populations, infrastructure and the built environment, this important volcanic hazard has so far received little systematic attention and there have been no attempts at quantitation. The purpose of this report is to consider issues arising from volcanic gas emissions in the event of a future AVF eruption. Here we introduce volcanic gases and discuss their hazards to human health, infrastructure, the built environment and aviation; we describe in detail three recent eruption case studies where gas impacts have been important; we describe the current arrangements for monitoring the relevant air pollutants in Auckland; we estimate fluxes of sulfur dioxide (SO2) for selected AVF eruption scenarios and put them in context alongside known anthropogenic sources of SO2 nationally, regionally and locally; and finally we identify key issues and knowledge gaps and provide recommendations on how these might be addressed. Estimates of gas emission rates for AVF eruption scenarios B and E suggest average and peak SO2 fluxes of ~650 t/d and ~1200 t/d. These fluxes are similar to the range of SO2 fluxes recorded for White Island volcano during 2019 and exceed total daily SO2 fluxes from all known anthropogenic sources in New Zealand by factors of 5-10. In relation to regional and local sources of SO2, new volcanic sources are expected to be even more dominant. A new AVF eruption will therefore be a major new air pollution point source in metropolitan Auckland. Impacts will depend on the following factors: vent location, meteorological conditions, populations and assets exposed, plume height and timing. For effective management of a future AVF eruption, we recommend developing improved capability for gas dispersion modelling and forecasting, improved capacity to forecast impacts of acidic volcanic gases on infrastructure and the built environment, and a multipronged approach to managing impacts on public health. (auth)