Who knew that a volcano erupting in the middle of a major city "can adversely impact human populations"?
Of course, your risk is greatly elevated if your city, such as Auckland, New Zealand (where I used to live) is "built on top of a volcano field."
Volcanic eruptions are a complex natural hazard, more appropriately described as a suite of natural perils occurring in parallel, in sequence, and/or multiple times in various combinations. The non-discrete nature of volcanic eruptions presents notable challenges in terms of eruption forecasting, response, and long-term management. Volcanic eruptions can adversely impact human populations in a number of ways, beyond killing or injuring individuals (e.g., Auker et al., 2013). Eruptions can prompt evacuations in an effort to minimise the number of fatalities (e.g., Tobin and Whiteford, 2002, Wilson et al., 2012a, Mei et al., 2013). Eruptions can also damage, destroy, or otherwise compromise infrastructure and services relied upon by modern societies, hindering response processes and daily life. Agriculture, horticulture, and forestry can also be impacted, affecting livelihoods and societal food sources. Finally, eruptions can directly and indirectly impact tourism and economic activity due to real or perceived danger and business disruption.
Given the potential for eruptions to cause devastating and catastrophic impacts, it is fortunate few urban centres are built directly on top of a volcano or volcanic centre. According to the Global Volcanism Program, only 6% of confirmed or presumed Holocene volcanoes have over 100,000 people living within 5 km of the volcano, and < 1% (12 out of 1532) have over a million people living within 5 km of the volcano. Most commonly, if an urban centre is exposed to volcanic hazards, it is exposed to volcanic ash or gas as these can reach areas at considerable distances from the source volcano. Volcanic ash is generally disruptive rather than destructive, and while often considered more of a nuisance, volcanic gas can cause health and agricultural impacts in situations where there are sufficient concentrations. Both volcanic ash and gas can present considerable challenges, but there are rarely major, long term or permanent changes to cities as a result; this is in contrast to the consequences of proximal hazards, which have historically caused considerable changes to or abandonment of inhabited areas.
What happens when an urban centre is co-located with a volcano or volcanic centre, and is thus exposed to proximal hazards in addition to volcanic ash and/or gas?
In this paper, we use a scenario approach to explore the potential consequences of volcanism within an urban centre. Specifically, we examine the implications of a monogenetic eruption for the city of Auckland, New Zealand, which is built on top of a volcanic field. Developing such information on future disaster risk is essential to underpin disaster risk management decisions to improve resilience.
From the introduction to:
Natalia I. Delinge, et al., "Investigating the consequences of urban volcanism using a scenario approach I: Development and application of a hypothetical eruption in the Auckland Volcanic Field, New Zealand" 336 Journal of Volcanology and Geothermal Research 192-208 (April 15, 2017).https://doi.org/10.1016/j.jvolgeores.2017.02.023
There are at least two well known examples of this happening catastrophically in the past, one in historic times, in the city of Pompeii in what is now Italy but was then part of the Roman Empire, and one at the boundary between historic and prehistoric times, in Santorini, Greece.