Hazard assessment of landslide-prone areas on highly weathered dunite rock in Bello Oriente, Medellín, Colombia (Project Inform@Risk)

The project Inform@Risk, a collaboration of German and Colombian Universities and Institutes funded by the German government, aims to install a landslide early warning system in the informal settlements in Medellín, Colombia. In the recent past the city has suffered from multiple landslides, some of them with up to 500 casualties. The informal settlements in the steep slopes at the city borders grow rapidly, which destabilizes the ground and complicates the installation and operation of an early warning system. Therefore, key goal of the project is to include the community in the process of the development of the early warning system.

Medellín is embedded in the Aburrá Valley in the Cordillera Central of the Andes. The region around the city consists of different triassic and cretaceous metamorphic rocks and magmatic batholites and plutonites. Especially the north-eastern slope is prone to landslides, as it is very steep and made up of a deep cover of soil over highly weathered dunite rock.

During the first field trip, carried out in August 2019, former landslide areas were located, and ERT-measurements were conducted at the study site Bello Oriente in the northeast of Medellín. After a first evaluation of the findings, the soil cover seems to be over 50 m high in the middle of the slope, which indicates a deep-seated landslide, that might have been moving downhill very slowly for thousands of years. The more dangerous landslides however, which are much faster, are the shallow ones on the surface. These landslides can appear on top of each other and are distributed across the whole study area but are most concentrated between and above the last houses of the barrio. During a second field campaign in 2020, the ERT-profiles will be calibrated and complemented by drillings and the hazard map will be completed accordingly.