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Abstract
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.
Highlights
Slope failure events in high-mountains globally hamper infrastructure and economic development, and cause hundreds of fatalities each year [1,2,3]
We focus on quantifying and discussing the mechanical characteristics of this mass movement leading to its translation into an enormous debris flow
In addition to the high-resolution images obtained from Google Earth for visual analysis, we mainly used two remote sensing datasets for performing quantitative analyses: (1) multi-temporal satellite images for surface velocity (SV) estimation and (2) high-resolution multi-temporal digital terrain models (DTMs) for Rapid Mass Movement Simulation (RAMMS) modelling
Summary
Slope failure events in high-mountains globally hamper infrastructure and economic development, and cause hundreds of fatalities each year [1,2,3]. Mass movements in high mountains can be characterised based on three main parameters [9]: (1) constituents involved (regolith, rock, glacial ice, and snow), (2) propagation velocity (slow, intermediate, and fast), and (3) characteristics of the movement (debris cloud, slurry, and coherent mass). An understanding of these characterising parameters further allows for a distinct classification of high-mountain slope failure events within categories, such as mudflow, debris flow, avalanche, landslide, rockfall, and debris fall.
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