The tragedy that stuck Uttarkhand's Chamoli on February 7 is remembered by all. A chunk of the Nanda Devi glacier broke off, triggering an avalanche, leading to flash floods and mass destruction in the area. 'A torrent of rock, ice, sediment, and water surged through the Rishiganga River valley past multiple villages and slammed into two hydropower stations,' leading to the death of 70 people.
Now, American space agency NASA's Earth Observatory has released satellite images that show a crack opening on an ice-covered flank of 6,029 metre-high Ronti mountain months before the landslide.
"On the morning of February 7, 2021, this spectacular terrain in Uttarakhand turned deadly when a torrent of rock, ice, sediment, and water surged through the Rishiganga River valley past multiple villages and slammed into two hydropower stations," NASA's Earth Observatory's report said.
"On February 21, 2021, the Operational Land Imager (OLI) on Landsat 8 captured a view of the landscape in the wake of the event. In the image above, natural-color Landsat 8 data were overlaid on a digital elevation model from the Shuttle Radar Topography Mission (SRTM) to depict the rugged topography," the report further said.
The satellite images show a closeup of the same area before (January 20, 2021) and after (February 21, 2021) the debris flow. It is important to note the dark scar near the origin of the landslide and the trail of dust and debris that blanketed the valley walls downstream.
According to the report published on NASA's Earth Observatory website, "Months before the landslide, satellite images showed a crack opening on an ice-covered flank of Ronti, a 6,029-meter (19,780-foot) mountain peak. On February 7, 2021, a huge chunk of a steep slope broke off from the peak, bringing down part of a hanging glacier perched on the ridge. After freefalling for roughly two kilometers, the rock and ice shattered as it slammed into the ground, producing an enormous landslide and dust cloud. As the accelerating rock and ice raced through Ronti Gad and then Rishiganga River valley, it picked up glacial sediments and melted snow. All the materials mixed into a fast-moving slurry that overwhelmed the river and churned wildly as it rushed through the river valley."
It remains an open question as to what caused the hanging glacier to fall in Uttarakhand but a group of scientists are trying to find an answer to that and other questions about the disaster. These scientists are "are analyzing several types of meteorological, geologic, and modeling data to supplement and contextualize the satellite imagery."
They hope to determine what role weather conditions, the tectonic environment, and shifting climate conditions might have played in priming the rock and ice for collapse. Dan Shugar, a geomorphologist at the University of Calgary said, "Unfortunately, there were no weather stations that we know of that were nearby, but we are looking at things like whether cycles of ongoing freezing and thawing may have weakened the rock."
"Climate change may have even helped destabilize the rock face through increased water infiltration over a period of years and by thawing permafrost. For now, we can hypothesize about these possibilities, but careful work is required to understand exactly what happened," he added.
