Lessons from 2019–2020 Landslide Risk Assessment in an Urban Area of Volcanic Soils in Pereira-Colombia

Abstract

The city of Pereira is in the central-western region of Colombia, in the valley of the Otún River in the Central Cordillera of the Colombian Andes, whose soils are mostly composed of volcanic ash and Lahar flows. On June 11, 2019, after intense rains, a landslide of about 13,000 m3 was triggered. This landslide killed 4 people, interrupted the traffic on an important national road, and endangered the airport runway. Just after the event, it was necessary to evacuate 100 homes, located in the upper part of the slope and 234 in the following days. A second landslide occurred on July 24, 2020, mobilizing 52,000 m3 and affecting 33 of the previously evacuated houses, then there were about 20 more small landslides. A zone of about 2.300 m long and 300 m wide (69 ha) was identified to be susceptible to new landslides that may affect more than 15.000 people. Identification of landslide triggering factors, failure, post-failure behavior, and the retrogressive landslide advance are reviewed because they are key factors for an effective hazard evaluation and risk governance. The landslide event was also used to calibrate a general methodological guide for landslide risk assessment, developed by the Colombian Geological Service and the National University of Colombia (Ávila et al. 2016) that has been extensively applied for the inclusion of risk evaluation in the land use planning, as required by the Colombian legislation.