Prediction of landslide occurrence in urban areas located on volcanic ash soils in Pereira, Colombia

As a result of the 25 January 1999 Armenia earthquake, the city of Pereira (400,000 inhabitants), located on a volcanic ash-covered alluvial fan in the western limit of the Central Cordillera (Colombia), suffered 250 slope movements. After a complete inventory, a monitoring process of unstable areas was designed, based on repeated topographic surveys, soil pore saturation levels and visual inspections. The participation of the communities was crucial and permitted the prediction of slope movements between 2 weeks and 3 months in advance and the evacuation of the inhabitants. Three specific examples are discussed. The method could be improved by excavating observation trenches and observing in detail local rainfall. In all cases, the strong involvement of the community was considered indispensable for the success of the process. © Springer-Verlag 2004