Frequent ice avalanche events are being reported across the globe in recent years. On the 7 February 2021, a flash flood triggered by a rock-ice avalanche with an unusually long runout distance, caused significant damage of life and property in the Tapovan region of the Indian Himalaya. Using multi-temporal satellite datasets, digital terrain models (DTMs) and simulations, here we report the pre-event and during-event flow characteristics of two large-scale avalanches within a 5-year interval at the slope failure site. Prior to both the events, we observed short-term and long-term changes in surface velocity (SV) with maximum SVs increasing up to over 5 times the normal values. We further simulated the events to understand their mechanical characteristics leading to long runouts. In addition to its massive volume, the extraordinary magnitude of the 2021 event can partly be attributed to the possible remobilisation and entrainment of the colluvial deposits from previous ice and snow avalanches. The anomalous SVs should be explored further for their suitability as a possible remotely observable precursor of ice avalanches from hanging glaciers. This sequence of events highlights that there is a need to take into account the antecedent conditions, while making a holistic assessment of the hazard.
Bibliographical noteThis article belongs to the Special Issue Applications of Remote Sensing in Glaciology
This research was funded from the Interdisciplinary Pump Priming Fund (grants nos.: SF10237-19 and SF10206-67) and Global Challenge Research Internal Funds (grant no.: SF10206-78) granted by the University of Aberdeen, U.K., and the Scottish Funding Council.
We acknowledge NASA, USGS, ESA, Planet Labs, and previous studies [36,40] for providing free-of-cost medium-to-high resolution satellite images and DTMs. We acknowledge the support provided by RAMMS Team at the Swiss Institute for Snow and Avalanche Research, Davos, Graubünden, in offering the RAMMS tool. We thank the reviewers for their constructive suggestions, which improved the quality of this paper.
Data Availability StatementAll the data used in this study is available free-of-cost in open access and the data sources have been cited. The simulation graphics have been provided as the Supplementary Materials.
- ice avalanche
- co-registration of optically sensed images and correlation (COSI-Corr)
- movement mechanics
- debris flow
- rapid mass movement simulation (RAMMS)
- glacier velocity
- high mountain
- hazard sequence
- mass movement mechanics