Auckland, New Zealand, is home to 1.4 million people, over a third of New Zealand's population, and accounts for ∼35% of New Zealand's GDP (Statistics New Zealand, 2014). The city is built on top of the Auckland Volcanic Field (AVF), which covers 360 km2, has over 50 eruptive centres (vents), and has erupted over 55 times in the past 250,000 years, producing a cumulative volume of ∼2 km3 of tephra, lava and other volcanic deposits1 (see Figure 5.1). The field is likely to erupt again: the most recent eruption, Rangitoto, was only 550 years ago. Most AVF vents are monogenetic, i.e. they only erupt once. This means that it is very likely that the next vent will erupt in a new location within the field. Despite considerable scientific efforts, no spatial (where) or temporal (when) patterns have been identified; indeed, the oldest (Pupuke volcano) and the youngest (Rangitoto) vents are located next to each other. As such, it is wholly unknown where or when the next eruption will be. The size of the next eruption is also difficult to address, as the last eruption, Rangitoto, accounts for nearly half of the erupted volume of the field, and it is unclear whether this eruption is an anomaly or signals a change in the eruptive behaviour of the field. These difficulties of assessing location, time and size of next eruption pose a considerable problem for emergency and risk managers. The main challenges facing Auckland and other populated areas coinciding with volcanic fields include:
• uncertainty of where and when the next eruption will take place;
• communicating to the public how an eruption of unknown location will impact them and how they can best prepare;
• planning for an event which hasn't occurred in historical time;
• foreseeing and appropriately planning for the range of possible impacts to the built environment, local, regional and national economy and psyche.