Little more than a year after the deadly ice-rock mass avalanche in Chamoli district in Uttarakhand that led to the death of more than 200 people and a substantial economic loss, scientists have been able to decode the reason behind the disaster.
Scientists of the Wadia Institute of Himalayan Geology have found that the region was seismically active before the disaster hit. They also found a noteworthy sequence of precursory signals of rock-ice detachment preceded by a formation of a new structure via self-assembly or self-organiSation called the dynamic nucleation phase.
“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. Also, the 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 study said.
Since its inception, the WIHG has been actively involved in understanding the processes responsible behind such disasters and focusing on detecting significant and unfelt activities with a dense network of seismic stations in the vicinity of Himalayan glaciers. As a part of this process, it also tried to trace the reasons behind the disaster that took place on February 7, 2021.
A group of nine scientists analysed the satellite images of the avalanche zone and found that it shows gradual growth of cracks and the joint near the crown of the weak wedge that has controlled the head scarp for the last five years.
“These cracks further started to open up and led to successive advancement of a weak zone near the crown of the wedge failure. The initiation of ice-rock mass avalanche has been recorded as seismic precursors, which were continuously active for 2.30 hours, before the main detachment took place,” the study published in the journal Scientific Reports said.
Scientists analysed and verified the seismic signals with field evidence to evaluate the velocity of dynamic flows and associated impacts. Such high-quality seismic data allowed them to reconstruct the complete chronological sequence and evaluate effects since the initiation to the advancement of debris flow.
Apart from the human loss, the impact of the flash flood was too high to sustain modern structures i.e., two hydropower projects, bridges and roads. The high-flow intensity of the flood disturbed the stability of the Raini village, and thus the area is prone to landslides, especially during the monsoon.
Seismic monitoring systems are well suited to detect mass movements such as debris flow, landslides, avalanches, etc. The ability to see such activities by a seismic network before the main failure could provide a scope for developing an early warning system for the region.
An integrated early warning system can alert the people towards the mitigation of any such impending disaster. The EWS 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 glacierised basins of the Himalayas, the study said.