The Landslide Hazard Chain in the Tapovan of the Himalayas on 7 February 2021

Abstract

On February 7, 2021, a catastrophic landslide occurred in Chamoli, India on the southern hills of the Himalayas (  30.37 N,  79.73 E). About 28 × 10 6 m 3 of landslide mass detached from the mountain face, entrained deposits in the valley and riverbed, and generated a huge debris flood along the Dhauliganga River. In this study, the geomorphological and volumetric characteristics of the disaster chain were interpreted from satellite images. The full process of the disaster chain and the erosion, deposition and flow discharge processes were reproduced using a cell-based analysis program, Erosion-Deposition Debris Flow Analysis (EDDA). The results indicate a peak flow discharge of the debris flood at Tapovan Hydropower Station of about 25,000-28,000 m 3 /s. The main erosion and deposition zones are distributed along the valley floor and the Dhauliganga River, respectively. This study serves as basis for understanding the disaster chain dynamics in high mountain areas.Plain Language Summary Catastrophic geo-disasters become more frequent in the Himalayan region due to the global climate change, and pose threats to the local residents and infrastructure. A large landslide happened in the Tapovan area in the south of the Himalayas on February 7, 2021, which triggered a large avalanche down the valley, entrained the deposits and river water, and evolved into a catastrophic debris flood in the Dhauliganga River, causing fatalities and severe damage to the local infrastructure. This study reconstructs the entire geo-disaster process, and reveals key characteristics including the landslide source, erosion and deposition features, and the transformation of hazard types. The outcome from this study helps understand and manage the risk of catastrophic geohazards in high mountain areas, especially in the Himalayas and other areas of the Tibetan Plateau. JIANG ET AL.

Reconstruction and Characterisation of Past and the Most Recent Slope Failure Events at the 2021 Rock-Ice Avalanche Site in Chamoli, Indian Himalaya

“…Therefore, for SF1, we opted for the variable friction values, which are automatically estimated by RAMMS, based on DTM-derived parameters (slope angle, altitude, and curvature), and we further provided forest information and the global parameters of the return period and avalanche volume. In case of SF2, the debris flow module of RAMMS needed to be initialised through a carefully selected combination of µ and ε, calibrated using the documented [21][22][23][24] timeand flow-related details of the event. This calibration was achieved through the observed runout extent on the post-disaster satellite imagery and the reported debris flow zones, flow heights, and velocities [21][22][23][24].…”

“…In case of SF2, the debris flow module of RAMMS needed to be initialised through a carefully selected combination of µ and ε, calibrated using the documented [21][22][23][24] timeand flow-related details of the event. This calibration was achieved through the observed runout extent on the post-disaster satellite imagery and the reported debris flow zones, flow heights, and velocities [21][22][23][24]. Thus, the model was precisely calibrated through extensive iterations to define the optimal friction values of µ and ε as 0.13 and 200 ms −2 , respectively.…”

“…A study [21] provided a detailed overview of the 7 February 2021 avalanche hazard cascade and modelled this event to be consisting of 80% rock and 20% ice volume, generating a total avalanche volume of ~27 × 10 6 m 3 . Two more studies [22,23] also adopted similar approaches to put a volumetric constraint on the 7 February 2021 event and described the possible chain of events that led to the extensive destruction. Another recent study [24] used satellite datasets to investigate and comprehend the possible causes for progressive destabilisation at the ice-rock interface.…”

“…In this paper, we intend to supplement these published studies (e.g., [21][22][23][24]) by focusing on the pre-event and during-event cascading flow characteristics using multi-temporal satellite datasets and robust rock-ice avalanche modelling approaches. We focus on quantifying and discussing the mechanical characteristics (momentum, pressure, and shear stress) of this mass movement leading to its translation into an enormous debris flow.…”

7 February Chamoli (Uttarakhand, India) Rock-Ice Avalanche Disaster: Model-Simulated Prevailing Meteorological Conditions

“…Geologically, the area of the rock-ice avalanche hosts central Himalayan crystalline rocks of meta-sedimentary origin [56]. Predominant rock types in this area are gneiss, kyanite-schist, quartzite, calc-silicate, marble, migmatite-gneiss, and quartz-mica schists from the Proterozoic age [57][58][59]. The elevation range of the rockslide body is about 5600 masl, and the slope angle of the sliding body just before the event was about 40 • [54].…”