Fogo, on the island of São Miguel in the Azores, is one of the most hazardous volcanoes in Europe. This paper is not concerned with the eruptive behaviour of Fogo, however, but rather with the hazard presented by its dynamic volcanic construct. This unstable construct is prone to slope failure, which finds expression in landsliding and the generation of mudflows/floods during periods of intense rainfall. Slope instability may also be caused by both volcanic and tectonic seismicity.
For instance, the large earthquake of 1552 triggered landslides on the lower south-east flank of Fogo which overwhelmed Vila Franca do Campo, the then capital of the island, killing around 5000 people. Often seismic and sub-aerial processes of hazard generation occur together so compounding their impact. As this paper is being prepared an on-going seismic crisis is occurring, with many earthquakes being felt on the eastern margin of Fogo. Periods of intense rainfall, a common phenomenon on São Miguel, present a further hazard on Fogo, because the deeply incised terrain concentrates surface runoff and produces dangerous floods. Recently floods swept through the village of Praia on the lower southern flank and in 1997 the Ribeira Grande overflowed during a spate causing extensive flood damage and a fatality.
Volcanoes such as Fogo are inherently unstable and immature landforms that present a hazard even during periods of volcanic repose. These hazards need to be understood to ensure that effective measures may be undertaken to mitigate the risk to communities who live on the flanks of volcanoes of this type.