Deadly Chamoli avalanche of 2021 due to preceding seismic activity, say scientists

Vijay Mohan

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Chandigarh, April 8

About a year after the deadly ice-rock mass avalanche in Chamoli district of Uttarakhand that killed over 200 persons, scientists have discovered that the region was seismically active before the disaster hit. This has been cited as the reason for the avalanche.

They have also recorded a “noteworthy” sequence of precursory signals of rock-ice detachment preceded by the formation of a new structure via a self-assembly process known as dynamic nucleation phase, the Ministry of Science and Technology said in a statement issued today.

A group of nine scientists from the Wadia Institute of Himalayan Geology (WIHG) analysed satellite images of the avalanche zone and found that it showed gradual growth of cracks near the crown of the weak wedge.

These cracks further started to open up and led to successive advancement of a weak zone near the crown. The initiation of ice-rock mass avalanche has been recorded as seismic precursors, which were continuously active for two-and-a-half hours before the main detachment took place.

Scientists analysed and verified the seismic signals with field evidence to evaluate the velocity of dynamic flows and associated impacts. High-quality seismic data enabled them to reconstruct the complete chronological sequence and evaluate effects since the initiation to the advancement of debris flow.

“Retreating Himalayan glaciers and associated melt along with unstable slopes are subject to trigger landslides by rainfall during monsoon or by induced seismicity in the region,” the ministry said.

“Snow, ice and rock avalanches may threaten people and infrastructure downstream in mountainous areas worldwide. This is why the area requires constant monitoring of seismicity as well as glacier status,” the statement added.

Apart from the human loss, the impact of the flash flood was too high to sustain the modern structures, i.e., two hydropower projects, bridges and roads. The high-flow intensity of the flood disturbed the stability of Raini village, and thus the area is prone to landslides, especially during the monsoon.

Stating that seismic monitoring systems are well suited to detect mass movements such as debris flow, landslides or avalanches, the ministry has stated that an integrated early warning system can alert the people towards the mitigation of any such impending disaster. The system should be based on seismic data from the seismometers, hydrological data from automatic water-level recorders and meteorological data from automatic weather stations installed as a network in the vicinity of a glacierised basin of the Himalayas.