11 December 2010
An initial assessment of the Bello landslide disaster in Colombia
Posted by Dave Petley
Over the course of the week more information has slowly come to light about the causes and nature of the Bello Landslide in Colombia last weekend. Most helpful is this Youtube video, which provides an overview of the site (and then some fairly harrowing but not graphic images of the rescue operation):
The Colombian newspaper El Tiempo continues to provide good coverage of the event (in Spanish of course) – the latest article is here. This reports that the number of victims is thought to be 119, of which 58 bodies have been recovered to date. Interestingly the article notes that the error margin is thought to be plus or minus 20%, and that a large unknown is the number of children who were playing in a playground that was buried in the landslide.
Based on the video above, and with help from a comment from Chris K earlier in the week, who correctly identified the area of the slide, I think the location is shown in the Google Earth perspective view below:
It is interesting to compare the archive imagery with this image, which was collected in 2008. In particular, this image from 2005 suggests that the area went through a huge amount of change, and in particular an increase in habitation, over the intervening three year period. The assumption must be that this continued in the two years after the most recent image:
It is interesting to note that the following screenshot from the video suggests that the crwon (top) of the landslide extended as far as the highway clearly visible in the Google Earth image above:
So let’s take a look at the Google Earth imagery of this area as well as looking at the image from the video:
Hmmm – I wonder if this is a fill slope upon which the road bench has been constructed? It looks suspiciously like that to me, though I can’t say for certain. It is interesting that this slope seems to have lost vegetation through time as well. So I wonder if the landslide was triggered by failure of an artificial slope below the road, which then loaded and entrained the material downslope to generate this large failure? That is certainly a good starting hypothesis I think, although a great deal of work is needed to determine what actually happened.
Comments or alternative models?
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
This is a terrible event that screams of the need for planners to better understand natural hazards.
It does look like fill was placed next to the highway.
Alternatively, in the top Google photo, it looks like there is quite a bit of land disturbance from the toe to about mid-scarp. Could the shoulder slope have been undermined?
At 0:07 in the video you see carves in the surface on the right hand side from the flow. These are in the satellite pictures straight below the landmarks you wrote about.
To me this looks like the flow started at the place of the factory (?) at the left corner of the pictures. I think there is even one of the buildings at the left corner of the picture taken from the video.
This area looks like freshly filled on the 2005 picture, while it is green on the 2008 photo.