Abstract
On 7 February 2021, Chamoli district (Uttarakhand, India) was devastated by a deadly rock-ice avalanche that led to a large causality of more than 200 people and a huge economic loss. We found noteworthy sequence of precursory signals of main failure/detachment preceded by a dynamic nucleation phase. The rock-ice avalanche appears to have been initiated by seismic precursors which were continuously active for 2:30 h prior to main detachment. The seismic amplitude, frequency characteristics and signal-to-noise ratio variation of detected tremors indicate static to dynamic changes in nucleation phase located at the source of detached wedge. The characteristics of seismic data distinguished debris flow and hitting obstacles from other seismic sources and allowed the estimations of debris flow speed. We analyzed and verified the seismic signals with field evidences to estimate the associated impacts and velocity of dynamic flow. The proximal high-quality seismic data allowed us to reconstruct the complete chronological sequence and evaluate impacts since the initiation of nucleation phase to its advancement. Furthermore, we suggest that real-time seismic monitoring with existing network and future deployment of integrated dense network can be used for forecasting of flow events and hazard mitigation in the downstream.
Highlights
The Himalayan glaciers are rapidly retreating due to increase in glacier melt and climate change in recent decades[1,2]
We found that the amplitude were generally higher for the horizontal components of the recorded seismic spikes/tremors attribute, which we understood as influence of surficial dynamics
We have analyzed seismic data of a deadly rock-ice avalanche (07 February 2021), its precursory signals and chronological advancement/impacts of dynamic events to reconstruct the entire scenario of devastation in Rishiganga–Dhauliganga valley of Chamoli district, NW Himalaya
Summary
The Himalayan glaciers are rapidly retreating due to increase in glacier melt and climate change in recent decades[1,2]. The recorded precursors of high-frequency continuous seismic tremors imply the active source dynamics, fracture propagation and subsequent flow of water in the cracks due to internally driven force in the weak section of the rock/material. The noise PSD analysis indicates the presence of high frequency noise during the wedge failure and subsequent flow of flash flood that is recorded in nearest seismic station (Fig. 4).
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