Auckland: when an eruption strikes, how long to evacuate a city?
It is not too long ago that New Zealand was exposed to a near-instantaneous volcanic event. In late 2019, Whakaari / White Island erupted with pretty much no notice, killing 22 people. Whakaari isn't too far from Auckland and indeed, Auckland (with its 1.2 million inhabitants) sits within the Auckland Volcanic Field - the hazard is evident.
Now, when a volcano erupts, the most useful and sure-fire way of reducing casualties is evacuation and recent work has attempted to understand how feasible this might be from the volcano-prone Auckland. The work highlights the fact that one of the most time-consuming aspects of such an evacuation might not actually be the evacuation itself but rather the time for authorities to determine that evacuation is indeed necessary and the time it takes to disseminate such a message; for Auckland, this timing was determined as 36 hours. Physical evacuation would then take 1-11 hours (depending on congestion).
There is a good deal of uncertainty in the modelling exercise. This uncertainly is chiefly related to the fact that there is no clear focus of volcanic activity in the city (53 volcanoes / possible volcanoes have been identified). Complete evacuation times will depend on where the eruption happens in relation to population and transport links: "A vent in the densely populated inner Auckland and CBD area would result in the greatest population required to evacuate, and also the greatest need for public transport support given the low vehicle ownership in this area".
Overall, the findings from such a study will be useful for the authorities, highlighting the importance of coming to timely and decisive decisions. The findings might also assist disaster planners in devising effective evacuation strategies, both in Auckland and also more widely.
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