What Satellite Imagery Told Scientists About April’s Nepal Earthquake

On April 25, a devastating 7.8 earthquake struck near the town of Gorkha, Nepal. Thousands of people lost their lives in Nepal and surrounding countries.

Jeffrey Kargel, a senior associate research scientist in the UA Department of Hydrology and Water Resources, was in Arizona thinking about how he could help. Kargel knows his way around satellite imagery thanks to his work as a glaciologist. He turned to this expertise to help find out exactly where landslides happened and get the data to officials and first responders.

Kargel, along with UA geologist Gregory Leonard, tapped their colleagues in the Global Land Ice Measurements from Space (GLIMS) for help. It’s like a club for glaciologists. They monitor glaciers all around the world. What started as looking at Himalayan glaciers to see the earthquake’s effects quickly shifted to looking for post-earthquake landslides.

Langtang before landslide

Town of Langtang in 2012. Credit: GlacierWorks

Soon after the earthquake, scientists teamed up with the NASA Applied Sciences Disasters group to use satellite imagery to help identify which areas were impacted the most and get help to them.

All they needed was up-to-date satellite imagery. And various government space agencies and commercial enterprises came through. After a quick request, the group of scientists had thousands of images to pour through. Six teams were organized to pour over each image to map out any potential hazards.

Computer models were also instrumental. They were used to evaluate how likely downstream edges of glacial lakes were to collapsing. Any collapse could threaten people living in the valleys below. Nearly 500 glacial lakes were surveyed. Only nine were affected by landslides. And satellite images showed no flooding from any of the lakes.

glacial lake

Armed with thousands of satellite images, scientists were able to give everyone from first responders to local officials information about potential hazards following the earthquake. The information gathered was also used by the International Centre for Integrated Mountain Development (ICIMOD) in a briefing with the Nepalese cabinet. And it led to additional support for a geohazard task force.

Fewer landslides than expected

Scientists were surprised by the number of landslides following the earthquake. In a six-week period following the earthquake, there were 4,312 landslides. “As horrific as this was, the situation could have been far worse for an earthquake of this magnitude,” said Kargel.

Another surprise is where the landslides occurred. We all know how earthquakes work. Two massive sections of the earth suddenly slip past each other. On the surface, this movement can translate to significant drops and rises. Radar imagery showed the Earth’s surface dropped nearly five feet in some areas and rose the same amount in others.

Overlay the landslide map with the radar map and an interesting pattern is revealed. Most of the landslides happened in areas where the ground surface dropped. Scientists didn’t expect this pattern, and it’s never been seen before according to Kargel.

Why did April’s earthquake cause fewer landslides? Kargel doesn’t have a definitive answer, but they’re looking into it. Eric Fielding of NASA’s Jet Propulsion Laboratory describes one theory. “Seismologists recorded relatively less shaking with seismometers in Kathmandu and other locations, and the smaller number of landslides suggests the shaking may have been reduced in the whole area.”