11 June 2021

Chamoli, Indian Himalaya: A massive rock and ice avalanche caused the 2021 disaster

Posted by Dave Petley

Chamoli, Indian Himalaya: A massive rock and ice avalanche caused the 2021 disaster

Back in February I blogged on a number of occasions about the terrible 7 February 2021 disaster in Chamoli, India, when a huge debris flow swept down a valley, with no warming, killing 200 peopleDan Shugar of the University of Calgary was the quickest off the blocks that day, using Planet Labs imagery to determine that the event was triggered by a rockslope failure.  Sadly there was a great deal of disinformation at the time, with even reputable scientists claiming that the event was a glacier collapse when the evidence was clear that this was not the case.

In the aftermath of the event a truly interdisciplinary team of researchers, from around the world but including scientists from India, self-organised to try to understand the event.  This team drew on skills from a diverse range of fields, including earth science, social science, seismology, remote sensing and modelling, to try to piece together what happened.  Over time the story became clear, with evidence to back up the interpretations.

The group was marshalled with great skill by Dan Shugar to produce a manuscript that documented the events.  In a matter of days this came together – the result was published yesterday by the journal Science (Shugar et al. 2021), and is available open access.

I don’t need to go into the detail of the sequence of events here – the abstract captures this well:

Our analysis of satellite imagery, seismic records, numerical model results, and eyewitness videos reveals that ~27×106 m3 of rock and glacier ice collapsed from the steep north face of Ronti Peak. The rock and ice avalanche rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders >20 m in diameter, and scoured the valley walls up to 220 m above the valley floor. The intersection of the hazard cascade with downvalley infrastructure resulted in a disaster, which highlights key questions about adequate monitoring and sustainable development in the Himalaya as well as other remote, high-mountain environments.

Figure 1 from the paper beautifully illustrates the initiating event at Chamoli:

Overview of the Chamoli disaster, Uttarakhand, India

Overview of the Chamoli disaster, Uttarakhand, India, from Shugar et al. (2021)


As I’m an author on the paper, it is not my place to comment on its quality.  I would like to highlight three key elements though:

The first is that Shugar et al. (2021) provides a very detailed explanation for the sequence of events at Chamoli.  It should lay to rest any suggest that this was anything other than a landslide. There may be details that will be refined over time, but the main sequence of events is clear.

Second, the paper demonstrates the amazing ability of a huge team to collaborate to bring forward an understanding of the sequence, even though this event occurred in a high mountain area in winter  in the middle of a pandemic when travel is impossible.  The keys were enthusiasm, ability, cooperation and extremely able leadership by Dan.

And thirdly the event highlights the perils of building infrastructure at great cost in areas subject to these events with understanding them properly.  Things must change is this event is not to be repeated.



D. H. Shugar, M. Jacquemart, D. Shean, S. Bhushan, K. Upadhyay, A. Sattar, W. Schwanghart, S. Mcbride, M. Van Wyk De Vries, M. Mergili, A. Emmer, C. Deschamps-Berger, M. Mcdonnell, R. Bhambri, S. Allen, E. Berthier, J. L. Carrivick, J. J. Clague, M. Dokukin, S. A. Dunning, H. Frey, S. Gascoin, U. K. Haritashya, C. Huggel, A. Kääb, J. S. Kargel, J. L. Kavanaugh, P. Lacroix, D. Petley, S. Rupper, M. F. Azam, S. J. Cook, A. P. Dimri, M. Eriksson, D. Farinotti, J. Fiddes, K. R. Gnyawali, S. Harrison, M. Jha, M. Koppes, A. Kumar, S. Leinss, U. Majeed, S. Mal, A. Muhuri, J. Noetzli, F. Paul, I. Rashid, K. Sain, J. Steiner, F. Ugalde, C. S. Watson, M. J. Westoby. 2021.  A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya. ScienceDOI: 10.1126/science.abh4455