11 March 2019
A video of a small but spectacular rockslide from Uttarakhand
A video has been posted onto Youtube showing a reasonably small but undeniably spectacular rockslide:-
In the comments section the location is described as being Uttarakhand, but no further details are provided. [Update – in a tweet SANDRP reports that the location is Bhatwadi in Uttarkashi district, and that the landslide happened last year] This appears to be to be as good an example as one could wish to find of a rockslide caused by discontinuities (joints) aligned with the slope – take a look at this still from the start of the video:-
The plane of weakness on which sliding occurred can be clearly seen. It appears that in constructing the road the toe of the landslide has been removed, leaving the rock blocks free to slide on that surface. Failure then occurs sequentially, with further failure of blocks at the toe of the slide destabilising the main rock mass. When sliding initiates the blocks move along this surface until free to fall:-
Once free, the mass rapidly fragments, although some large blocks remain intact:-
This is a fine example of the need to ensure that rock slopes are properly assessed and, where appropriate, engineered to prevent failure. The need for a proper engineering approach has been described in detail over the last 30 years by Dr Gareth Hearn. He has a good presentation summarising the key issues (NB PDF). The techniques for preventing this type of failure are well established and comparatively simple to implement, but in many mountain areas a combination of a lack of resource and a lack of expertise mean that this does not happen. The upshot is increased disruption, high levels of hazard and, when the slope fails, substantial environmental cost.