In a paper released last week in Science, researchers shared
how they used Planet satellite data, combined with eye witness
accounts, video on the ground, and other remote sensing datasets,
to determine the cause of the massive debris flow that cascaded
through valleys in Chamoli, Uttarakhand, India on February 7, 2021.
The event killed dozens, with over 150 more missing. Two hydroelectric
power stations experienced over $223 million in damage as the landslide
made its way downslope, scouring rock and flattening forests. Planet’s
satellites captured imagery that revealed critical information about
what triggered this devastating event.
Based on seismic measurements on the ground, the landslide began at
4:51 UTC, traveling down the valley at nearly 60 meters (~200 feet) per
second. Initial news reports stated that a glacier outburst flood triggered
by a collapsing glacier was to blame. However, an international team of
landslide experts led by Dr. Dan Shugar at the University of Calgary was
able to quickly prove otherwise using PlanetScope imagery. Accessing
imagery through Planet’s Education and Research Program, the team downloaded
and analyzed imagery within hours of the landslide occurring—making
news the very same day.
Planet’s Dove satellites passively image Earth’s entire landmass on a
near-daily basis and were therefore able to capture imagery of disaster
areas without the need for tasking. A Dove satellite passed over Chamoli
at 5:01 UTC, a mere 10 minutes after the landslide began. Then, 27 minutes
later, another Planet satellite imaged the same area, capturing the dynamics
of the landslide in motion. Shugar’s team coordinated with Planet to
rapidly acquire high-resolution SkySat imagery of the affected areas
within hours. By analyzing these images, combined with eye witness accounts
and video on the ground and other remote sensing datasets, Shugar and
team were able to determine that the cause of the landslide was actually
a massive rockfall at a location called Ronti Peak—one of the largest
rockfalls ever recorded, collapsing from a height of about 3400 meters.
Glacial meltwater, heavy rainfall in the preceding days, and water released
from the hydroelectric power stations may have all contributed to the
unusually high speed and mobility of the landslide as it progressed
through the valleys.
“Although we cannot attribute this individual disaster specifically to
climate change, the possibly increasing frequency of high-mountain slope
instabilities can likely be related to observed atmospheric warming and
corresponding long-term changes in cryospheric conditions (glaciers,
permafrost),” Shugar and team note in their paper.
The pace at which this research was conducted was striking: four months
from the date the landslide occurred to the date the paper was published.
A team of over 50 scientists across fourteen countries mobilized to make
this happen. “It was a pretty amazing experience to work with the very
best in the field, and from all around the world,” Shugar says. “At nearly
every hour of the day for a month, someone was working on some aspect.”
Early warning systems, combined with education on risks and actions to
take in the event of an emergency, could help to save lives in landslide-prone
areas like the Himalayas. “Videos of the event, including ones broadcast
on social media in real time, showed that the people directly at risk had
little to no warning,” Shugar and his team said. However, analyzing older
satellite imagery, they found visible evidence of the slope that eventually
failed and triggered the landslide had been moving since at least 2016—an
early warning sign of the devastation to come. Monitoring for the signs of
slope instability with satellite imagery can play a key role in taking
preventative measures and deploying warnings to those in the potential path
of danger, helping to save lives.
Provided by the IKCEST Disaster Risk Reduction Knowledge Service System