9 October 2020
Rest and Be Thankful: the cause of the landslide problems
In recent years a key strategic highway in Scotland, the A83, has repeatedly been blocked by landslides at the rather beautifully named Rest and Be Thankful. This road provides the main access from north of Glasgow to a large part of western Scotland. The alternative routes involve a long detour.
I recently drove along the road, and stopped at the viewpoint to photograph the problematic slope. This is one of my images:-
This is a steep slope that is heavily dissected by drainage lines (channels). The underlying geology is the Beinn Bheula schist formation. In my experience schists are often associated with slope instability, but in this case the problem is the material that sits on top of the bedrock. At Rest and Be Thankful this is a comparatively thick layer of colluvium – deposits left from earlier phases of slope instability – and varying amounts of topsoil and peat. These materials are susceptible to failure in heavy rainfall. Unfortunately, as the intensity of rainfall increases due to climate change, and the United Kingdom is getting longer spells of rainy conditions as well, repeated failure is occurring. As the image shows (and note the bus for scale on the lift side of the image), there is a vast amount of potentially unstable material on the slope.
The image below highlights the nature of the instability:
Note the vehicles for scale again. This image shows multiple sources of instability, and at least one ongoing failure. Note also the extensive use of flexible barriers to attempt to retain the debris. The image illustrates why the capacity of these barriers is being exceeded by the regular slope failures.
As I drove through the very extensive works at this site I shot a video using a dashcam, which I have uploaded to Youtube:
An 18 year old Land Rover Defender is probably not the ideal stable camera car, and hence the video is a little wonky, but it gives a sense of the scale of the works at the site. It is hard to believe that we will not continue to see extensive disruption at this site into the future, despite the best efforts of the engineers. The road was closed yesterday (8 October 2020) as a precaution due to heavy rainfall.
Quickslide 1: 15 years after the Kashmir Earthquake
Yesterday was the 15th anniversary of the devastating 08 October 2005 Kashmir earthquake, which may have killed 100,000 people. Landslides were a very substantial cause of loss of life in that dreadful event.
Quickslide 2: Landslides on asteroid Bennu
A new paper in Science Advances describes probably the most exotic landslides to date – potential slope failures on Asteroid Bennu. The authors speculate that the asteroid has undergone rotational failure to generate longitudinal ridges. There is also some evidence of toppling failure.