Nepal – Monsoon Rain to Increase Landslide Risk on Slopes Weakened by Earthquake

Researchers from the University of Michigan say that the threat of landslides and mudslides remains high across much of Nepal’s high country after the huge earthquake of 25 April 2015. Furthermore, the risk is likely to increase when the monsoon rains arrive this summer, which in turn could increase flood risk.

Landslides in mountainous regions can block river valleys, creating a significant flooding hazard. Water builds up behind those dam-like structures, creating the potential for catastrophic flooding if the dams are overtopped and then fail.

Marin Clark and two colleagues from the University of Michigan have assessed the landslide hazard in Nepal following the devastating earthquake which, according to latest figures, has left over 5,000 dead and 10,000 injured.

The team looked for locations where landslides likely occurred during the earthquake, as well as places that are at high risk in the coming weeks and months. Clark said:

“The analysis revealed tens of thousands of locations at high risk”

“The majority of them, we expect, have already happened and came down all at once with the shaking on Saturday (25 April),” she said. “But there will still be slopes that have not yet failed but were weakened. So there will be a continued risk during aftershocks and with the recent rainfall, and again when the monsoon rains arrive this summer.”

“The satellites looked first at places where lots of people live, including Kathmandu and the foothills areas to the south,” Clark said. “Those areas do not look significantly impacted by landsliding, but we’re worried about the high country,” she said.

The region at highest risk for landslides and mudslides is the mountainous area along the Nepal-Tibet border, north of Kathmandu and west of Mount Everest, directly above the fault rupture. The highest-risk zone is at elevations above 8,200 feet in a region that covers 17,550 square miles.

Image: University of Michingan
Image: University of Michingan

Sindhupalchowk Landslide 2014

A massive landslide that struck in the Nepal district of Sindhupalchowk on 01 August 2014 blocked the Sunkoshi (Sun Kosi) river, creating a lake three kilometres by 300 metres. Nepalese military engineers, assisted by engineers from India, worked to unblock the river to find a way to allow safe controlled runoff of the water using controlled blasts. At one point the newly created lake threatened to flood vast areas of Bihar, India, as well as Nepal.

nepal landslide
Landslide at Sindhupalchowk, Nepal, August 2014. Photo: Nepal Army

For more information on the University of Michigan study, see the statement here.

For more information about the Nepal earthquake, see Relief Web here.