Preprints
https://doi.org/10.5194/nhess-2021-333
https://doi.org/10.5194/nhess-2021-333

  10 Nov 2021

10 Nov 2021

Review status: this preprint is currently under review for the journal NHESS.

Pre-collapse motion of the February 2021 Chamoli rock-ice avalanche, Indian Himalaya

Maximillian Van Wyk de Vries1,2, Shashank Bhushan3, Mylène Jacquemart4,5, César Deschamps-Berger6, Etienne Berthier7, Simon Gascoin6, David E. Shean3, Dan H. Shugar8, and Andreas Kääb9 Maximillian Van Wyk de Vries et al.
  • 1St Anthonys Falls laboratory, University of Minnesota, Minneapolis, MN, USA
  • 2Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA
  • 3Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA
  • 4Laboratory for Hydraulics, Hydrology, and Glaciology (VAW), ETH Zurich, Zurich, Switzerland
  • 5Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), Birmensdorf, Switzerland
  • 6CESBIO, Université de Toulouse, CNRS, CNES, IRD, INRAE, UPS, Toulouse, France
  • 7LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France
  • 8Water, Sediment, Hazards, and Earth-surface Dynamics (waterSHED) Lab, Department of Geoscience, University of Calgary, Canada
  • 9Department of Geosciences, University of Oslo, Oslo, Norway

Abstract. On the 7th of February 2021, a large rock-ice avalanche triggered a debris flow in Chamoli district, Uttarakhand, India, leaving over 200 dead or missing. The rock-ice avalanche originated from a steep, glacierized north-facing slope. In this work, we assess the precursory signs exhibited by this slope prior to the catastrophic collapse. We evaluate monthly slope motion from 2015 to 2021 through feature tracking of high-resolution optical satellite imagery. We then combine these data with a time series of pre- and post-event DEMs, which we use to evaluate elevation change over the same area. Both datasets show that the 26.9 Mm3 collapse block moved over 10 m horizontally and vertically in the five years preceding collapse, with particularly rapid motion occurring in the summers of 2017 and 2018. We propose that the collapse results from a combination of snow-loading in a deep headwall crack and permafrost degradation in the heavily jointed bedrock. Our observation of a clear precursory signal highlights the potential of satellite imagery for monitoring the stability of high-risk slopes. We find that the timing of the Chamoli rock-ice avalanche could likely not have been forecast from satellite data alone.

Maximillian Van Wyk de Vries et al.

Status: open (until 23 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Maximillian Van Wyk de Vries et al.

Maximillian Van Wyk de Vries et al.

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Short summary
On the 7th of February 2021, a large rock-ice avalanche occurred in Chamoli, Indian Himalaya. The resulting debris flow swept down the nearby valley, leaving over 200 people dead or missing. We use a range of satellite datasets to investigate how the collapse area changed prior to collapse. We show that signs of instability were visible as early five years prior to collapse. However, it would likely not have been possible to predict the timing of the event from current satellite datasets.
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