The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
Last week marked the 50th anniversary of the 28 June 1974 Quebrada Blanca landslide disaster in Colombia, in which up to 500 people were killed. There is a good video, in Spanish, on Youtube that marks the anniversary. However, there is remarkably little detail of the landslide in English, and very few images of the aftermath of the accident.
The event has a Spanish Wikipedia page, which describes the sequence of events, and there is also a very good account in El Tiempo. The location was a major highway, the Carretera al Llano, which links the cities of Bogota and Villavicencio. In the Quebrada Blanca sector of the road, landslides were a constant problem, destroying infrastructure and closing the road. Stabilisation works were undertaken, but problems persisted.
In early June 1974, a large crack developed in the hillslope above Quebrada Blanca. The crack was 315 metres in length, indicating that a volume of about 473,000 cubic metres had become mobile.
A decision was taken by those managing the road to try to induce failure of the slope. Reports indicate that measures included the use of explosives, the injection of water into the mass and even the use of artillery to try to trigger the landslide.
On 22 June 1974, a small failure occurred, damaging a bridge. In the aftermath the road was cleared, and some movement of traffic was permitted.
The contemporary reports indicate that the management of traffic was exceptionally poor. Travelers trapped by the closure of the road actively demonstrated about the delay to their journey. A huge traffic jam developed through the landslide affected area, in part because the road was obstructed by a broken down vehicle.
Tragically, on 28 June at about 4 pm, on a Friday afternoon at the start of a holiday weekend, the slope collapsed. It is estimated that the final volume of the failure was between 500,000 and one million cubic metres. At the time of the failure, there were hundreds people on the road directly in the path of the landslide.
Estimates of the final death toll range from about 300 to over 600 people. The remains of only 27 people were recovered.
The Servicio Geologico Colombiano (the Colombian Geological Service) has a good webpage about the landslide (in Spanish), which includes this image of the site as it is today:-
The Servicio Geologico Colombiano article draws the following conclusion about the landslide:-
“In geo-environmental terms … all possible geological, climatic and anthropic conditions came together to give rise to the tragedy. On the one hand, the fact that the area is undergoing an active uplift of the mountain range had an influence, which not only generates earthquakes and constant movements due to the conflicting forces of the tectonic plates, but also the formation of convex slopes several kilometers long that are more prone to erosion by water.”
“Added to this was the rainy season, which had forced the road to be closed weeks before due to small landslides that required earth removal work. The action of the water from the season’s rainfall infiltrated the upper part of the terrace, saturating the materials. Additionally, permanent erosion prevented the growth of vegetation that would act as protection. Finally, the unpredictable fact that the landslide occurred on the Friday of a holiday weekend when more people than usual were rioting at the road closure, increased the dimension of the tragedy.”
The highway between Cáqueza and Villavicencio continues to suffer from landslide issues. Work is now underway in the Quebrada Blanca catchment to better understand the hazard, in the hope that it will open the door to improved safety and resilience along the road.