Building cities in a subduction zone: Some Indonesian dangers

This chapter seeks to assess the future risks to Indonesian mega-cities by examining the record of tectonically generated disasters in the past. It argues that there are two clear trends, to some extent balancing each other. On the one hand, the quantifiable impact of natural disasters is growing as populations increase and concentrates ever more in endangered coastal mega-cities. On the other, global advances in communications, and scientific understanding of the dangers of eruptions, tsunamis and earthquakes, provide unprecedented opportunities for preparedness. A third factor appears to be cyclical. Indonesian cities were (badly) planned and built, and attracted half the Indonesian population to endangered coastal locations, during a century which was unusually mild in terms of both volcanic eruptions and tsunamis. Since 2004 it has become clear that mega-tsunamis must recur every few centuries to release the build-up of pressure in Indonesian subduction zones. The periodicity of megaeruptions is harder to predict, but even a repetition of the 19th century pattern would bring not only unprecedented death and destruction in the 21st, but incalculable disruption to agriculture and air transport.