27 June 2015
Lac du Chambon – a rapidly failing landslide that has disrupted the Tour de France
Posted by Dave Petley
Lac du Chambon
On the banks of the Lac du Chambon in the French Alps a 1 million cubic metre landslide is rapidly developing. This landslide is making the international news because it has caused the organisers of the Tour de France to reroute perhaps the most famous section of all – the Alpine stage that ends with the lung-bursting climb to the ski resort of Alpe d’Huez.
The slope in question on the edge of the Lac du Chambon is important because the road along the edge of the lake bypasses it via a tunnel that passes through the landslide mass. This is a Google Earth perspective view – the road is the yellow line, with the tunnel section being the part of the road that is missing:
Interestingly, there is no obvious indication of instability in this image (from 2009), but there is a large landslide scar on the left side of the mass (the tunnel portal is clearly located on the edge of the landslide scar). The landslide itself is now heavily disrupted, as per these images from 3France:
In recent days the movement rate of the landslide has accelerated from 5 to 15 cm per day, suggesting that the landslide might be in a tertiary creep phase. However, as the Mount Mannen landslide in Norway last year demonstrated, predicting failure is very challenging, and the team monitoring the landslide are sensibly making no firm predictions. Of course, it will be very challenging for the authorities if the slope does not collapse.
There is some interesting footage of the inside of the tunnel in the video embedded in this web page, which should be visible below:
This is a still from the video, showing the level of internal deformation that is occurring within the landslide:
This is of course a wonderful opportunity to get a better understanding of both the dynamics of a large slope failure and the way in which the displacement wave will develop and propagate. I hope that it will be possible to collect a detailed dataset and some video of the development of the failure.