1 October 2020
An interesting video showing large-scale liquefaction in a landslide
The end of the summer monsoon in South Asia had a significant bite this year, with a spate of landslides in both northern India and Nepal in late September. These proved costly once more. I have yet to fully analyse the impact of landslides in Nepal in the 2020 summer monsoon, that will be for a future post, but there is little doubt that it will prove to have had the highest number of fatal, rainfall-induced landslides on record.
An interesting video has been published on Youtube, showing a slope failure that apparently occurred in Shillong. I cannot find any detail about this landslide, and so cannot confirm the location or the date, but the video is interesting and informative. This is the video:-
This starts off as a reasonably large shallow translational slip on a quite steep slope. The inference is that prior to failure this material had a reasonably high shear strength, enough to maintain that steep slope angle:-
A second or so later the slip reaches the building at the toe of the slope. By the point it has gone through liquefaction and is now behaving as a fluid:-
Indeed the portion of the landslide deposit closest to the camera literally flows away, but of course this may have entrained additional water from within the channel.
This is a very stark illustration of the destructive power of even moderately-sized slips. It is fortunate that the building was robust – one can imagine the impacts on a flimsy structure – although it is likely that the people living at that end of the building were significantly impacted.
As always the key take home message is to prevent the slope from failing in the first place.