13 August 2021
Nalda: a valley-blocking landslide in Himachal Pradesh, India
Posted by Dave Petley
Nalda: a valley-blocking landslide in Himachal Pradesh, India
This morning (Friday 13 August 2021) a major landslide occurred near to the village of Nalda, in Lahaul and Spiti district in Himachal Pradesh, northern India, blocking the Chenab River. The landslide event itself was captured in a video that has been posted to Youtube:
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The landslide has left a large barrier across the Chenab River close to Nalda. The image below, from Tribune India, provides an overview of the situation:
The valley blocking landslide close to the village of Nalda in Himachal Pradesh in northern India. Image from Tribune India
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This is not likely to remain breached for long given the topography of the land and the form of the barrier – indeed some reports suggest that some flow has been re-established. But even a few hours of impounded water has the potential to generate a substantial local flood, so there is a substantial hazard for villages downstream.
Note the very clear planar structures in the landslide scar. The failure is clearly defined by two existing joints or faults, meeting with a c.90 degree angle. Note also the landslide scar immediately to the left of the landslide scar. That must also have been a substantial failure event.
This landslide comes on the back of a significant landslide in India on Wednesday, when a slope above a road in India collapsed, burying several vehicles including a bus. Recovery operations continue at the site, but at the time of writing 15 bodies have been recovered. There are fears that there may be substantially higher levels of loss. The Indian Express reports that Chief Minister Jai Ram Thakur has indicated that up to 60 people were feared trapped under the debris at the time of the accident. Rescue operations are being hampered by ongoing instability on the slope.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Hello Dave,
How can you identify the “two existing joints or faults” from the video/picture ? I am struggling to figure it out myself 🙂
Thanks
[The nataural plan form of the scarp, in the absence of other controls, would be arcuate. This slide differs from that in that it has a very planar rear scarp, with a sharp “corner” to another planar surface forming the pseudo lateral scarp. These two planes form a wedge. These are the two existing joints or faults. D.]
In my view an old landslide mass existing in this place has been triggered due to undercutting by the river resulting a slumping of toe of landslide along a weak plane.
Such cases are seen along the major rivers in Himalayas where landslides have resulted in river blockage and the breach resulted in downstream floods..
Dear Dave
Thanks for your effort to keep the blog running and giving an excellent source of updated and edited information on landslides.
I would like to confirm if my interpretations of this case, based on the photograph, is correct: the landslide scar surrounding area morphology suggests it is composed by talus deposits and not bedrock. I seem to me that the large scale talus deposits control the position and are cut by the river, oversteepening the slope and causing unstable conditions. It seems to me (but the photo has low resolution) that the smooth landslide scar also suggests a soil like material failure.
Thanks and best regards
Dear Dave
Thanks for your effort to keep the blog running and giving an excellent source of updated and edited information on landslides.
I would like to confirm if my interpretations of this case, based on the photograph, is correct: the landslide scar surrounding area morphology suggests it is composed by talus deposits and not bedrock. I seem to me that the large scale talus deposits control the position and are cut by the river, oversteepening the slope and causing unstable conditions. It seems to me (but the photo has low resolution) that the smooth landslide scar also suggests a soil like material failure.
Thanks and best regards
For more details, see: https://sandrp.in/2021/08/14/landslide-dam-on-chenab-river-in-himachal-pradesh/
Thanks,
Himanshu Thakkar (SANDRP)
This isn’t about this landslide but there was a sizeable landslide in a bean field near the Red River in Minnesota:
https://strangesounds.org/2021/08/bean-field-collapses-minnesota-video-pictures-polk-county.html