The increasing exposure of cities to the effects of volcanic eruptions: a global survey

The most dynamic demographic process of the past 250 years has been the movement of people from rural areas to cities. For most of this period urbanisation has been concentrated in economically more developed parts of the world, but during the last 50 years the focus has shifted to economically less developed regions. Urbanisation, particularly in developing countries, has led to increasing global exposure to a variety of natural hazards, not the least of which are risks posed to large cities by volcanoes. In this paper we monitor these demographic changes and detail the various types of volcanic hazard to which cities are exposed. A major eruption affecting a city in a developing country could cause widespread loss of life and regional disruption. Effective response, however, might minimise casualties in a city within a developed nation affected by a major eruption, but the economic impact could have global consequences. We argue that global hazard exposure is often subtle and involves not only the size of a city and the types of volcanic product that may occur, but also the strategic position of the threatened city within the economy of a country and/or region and the fact that volcano-induced tsunami and other consequences of eruptions, such as climatic change, may affect cities far removed from a given eruption site. Mitigation measures informed by both specific prediction (surveillance) and general prediction (hazard mapping) are providing the potential to reduce hazard exposure. The paper concludes with a consideration of ongoing research, in particular the emphasis currently being placed on conflating hazard analysis with studies of place, economy, society and culture.