The Mountain Research Initiative Coordination Office was extremely saddened to hear news of the flood/debris flow disaster that occurred in the mountainous Chamoli district of Uttarakhand State, India, on the morning of 7 February 20211.

At the time of writing (11 February), 34 people are known to have lost their lives, and at least 174 people remain missing2. Two hydropower stations and other infrastructure, including roads and bridges, were destroyed. We hope that the remainder of the rescue and recovery operation will proceed as efficiently as the challenging circumstances in this fragile social-ecological system allow. Several members of the MRI network, in conjunction with Indian scientists, are contributing to develop an understanding of the event and its impacts.

The cause(s) of and contributory factors to the hazardous event and ensuing disaster, including the precise chain of events and their timing, currently remain somewhat unclear. A considerable volume of bedrock and glacier ice (~5-15 × 106 m3 or even more) in the Nanda Devi massif is known to have released at an elevation of approximately 5,600 m a.s.l, whereupon it descended the steeps slopes over two thousand vertical metres to the valley floor below3. This mass movement subsequently mobilized an extreme amount of water from melting avalanche ice and snow, and entrained water stored in sediments and flowing in the rivers. The result was a devastating floodwave of water, mud, and debris in the Rishi Ganga and Dhauligarga Rivers, which was responsible for the deaths and damage recorded. In this sense, the event certainly seems to have conformed to the notion of complex, cascading, “multi-hazard”.  

Water moving through the dam site. Source: Guardian News, via YouTube.

Speculation has been intense regarding the roles of several (potentially interrelated) factors, including the extent to which some may have been modulated by anthropogenic climate change, for instance:  

  • The implications of a horizontal crack (crevasse) in the ice that, post-event, high-resolution satellite imagery showed to have widened rapidly in the preceding days (e.g. advecting heat and possibly also meltwater to the glacier bed);
  • The extent to which permafrost thaw and/or freeze thaw action could have been responsible for the failure along bedding planes in the underlying bedrock;
  • The extent to which liquid water was present at the glacier bedrock interface, which could have provided a lubricating effect;
  • The possible role of warming atmospheric temperatures following a cold and snowy period (now thought to be of only minor if any significance); and
  • The possible minor effects of direct anthropogenic interventions downstream, such as tree removal and river dredging, although the large magnitude of this event probably renders any such impacts negligible.

Detailed field investigations and local data and observations corresponding are required to better elucidate the triggers and process interactions that occurred.

It can now however be stated with some confidence that contrary to many initial reports, the event was not associated with a classical glacial lake outburst flood (GLOF); there having been no such lakes in the vicinity. Others have variously suggested that the event’s origins lie in “snowbank melt and slumping”4, or that a rockfall from above onto the glacier triggered the detachment of ice and landslide, behind the runout of which water may have accumulated unconsolidated landslide sediments for several days before warming, freeze-thaw conditions led to its breach5. However, these explanations do not accord well with the insights gleaned from that highly spatially and temporally resolved satellite images pertaining to event that were obtained (especially the timing and the presence of dust from bedrock)3.

Perhaps the most uncertainty relates to the source of the considerable volume of water that contributed to the devastating flood wave3. Firstly, it seems likely that any entrained ice and snow in the path of the avalanche landslide would have been melted via impact energy and frictional effects, representing one water source3. In addition, it is possible that tributary valleys were temporarily dammed by the debris flow, water accumulated behind these structures, and then they subsequently breached catastrophically3. However, the short lag-time between the detachment of the bedrock and ice and the destruction of the Tapavan hydropower station does not necessarily sit easily with this narrative, as there may have been insufficient time for such considerable volumes of water to accumulate. As noted above, unconsolidated valley fill sediments that were saturated with water could also have been entrained by the landslide/debris flow, perhaps combining with perhaps considerable volume of water that was released from the resevoir of the upper dam (located near Raini village). Finally, it remains possible that the direct impact of the avalanche/landslide on the river caused a wave to be propogate3.

Future efforts in two primary areas could be useful. In the short term, all potentially relevant available data – both in situ (as available) and remotely sensed – should be rapidly collated. Unfortunately, meteorological information, river flow data, and seismic records from in situ stations in the broader region, which could provide crucial insight, do not appear to be available or accessible online. Certainly, the chasm therefore growing between the availability of remotely sensed and in situ data appears to be widening. This is important, of course, because some potentially critical variables simply cannot be measured remotely. Once collated, given the cascading nature of the event, all data should be interpreted in such a way that integrates interdisciplinary and transdisciplinary knowledge and perspectives. Ideally, such work should also be undertaken similar regions that could be at high risk from similar events.

In the longer term, it is inevitable that in such high, remote, steep, sensitive, rapidly warming, and deglaciating environments, large infrastructure projects can be exposed to considerable natural risks (sensu hazard × vulnerability × exposure). However, a paucity of long-term, informative data, the likelihood of climate change-induced non-stationarity, and the complex, cascading nature of such events make these risks extremely challenging to quantify reliably. It may therefore be appropriate for the viability of such infrastructure projects to be reappraised. At the very least, in order to protect people and infrastructure who are inherently in harm’s way (e.g. hydro-electric power stations), ongoing multi-variate monitoring of upstream environments, coupled with early warning systems that exploit modern technology and associated mandatory drills, would seem imperative.

The broader region was also affected by devastating flooding in 2013, leading to over 5,000 deaths6. Therefore, there also appears to be considerable scope to refine hazard mapping efforts in the region7 more generally. Alongside appropriate land use planning policies, such information can provide more effective understanding and differentiation of hazard amongst local populations and authorities, and ultimately improved mitigation actions. To support this, it would be important to make meteorological, river gauging, and seismic station data freely available for all non-commercial purposes. Appropriate data policies and delivery systems / portals could be developed in conjunction with international organizations who have previously followed a similar path.  

The MRI and one of its Flagship Initiatives – GEO Mountains – stand ready to contribute to such efforts in any way possible, and in so doing reaffirm our commitment to responding to the Call to Action that resulted from the WMO High Mountain Summit of 2019, of which MRI Executive Director Dr. Carolina Adler was Co-chair. In particular, we strive to increase the observations of Earth system processes in mountains terrain and the availability and usability of the corresponding data, provide networking opportunities and fora in which a diverse range of stakeholders can collaborate to drive progress, and together providing data and information to support effective disaster risk mitigation and sustainable development policies – all of which will be crucial for minimizing the consequences of such events whose frequency and severity are likely to increase in mountain regions across the world.

3GAPHAZ. First insights into the Chamoli disaster, 8 February 2021 (version 8 February 2021). See: For an updated assessment (20 February 2021) by the group, see here.

Further Reading

Cover image: Nanda Devi from the west by Michael Scalet, CC BY-SA 2.0, via Wikimedia Commons.

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