25 November 2018
Video: a spectacular double flow-type failure from Kerala, India
I have come across a spectacular video of flow-type landslide, apparently collected in Kerala, India. The video, which was posted to Youtube on 21st November 2018, has no detailed explanation associated with it. That is unfortunate as it is genuinely spectacular. The video should be visible below:-
The landslide appears to occur in two phases, initially a dynamic failure that splinters and destroys the trees bordering the river:-
Note that this landslide has clearly stated much higher up the slope as after the slide a track is visible disappearing into the distance. This initial failure is then followed by a very large, very rapid flow type failure along the track of the first landslide:-
This second phase is much more rapid, with a higher volume, than the first. It is sufficiently mobile that the flow crosses the river, even though it is in flood, and super-elevates to the level of the observers. This could have been very serious.
The origin of this double failure is not clear, but I am reminded of the very dramatic Lantau island landslides in Hong Kong in 2008, one of which was also caught on video. These started as comparatively small, shallow failures high on the hillside that transitioned into large-volume, channelised debris flows that entrained significant amounts of material. Note that in the case of the Kerala landslide in this video that material involved appears to be deeply weathered (red in colour) soil and rock, which might also hint at a similar mechanism.
It is rare to capture a channelised flow such as this coming straight at the camera. That they cause such high losses is unsurprising in light of this video.