On April 25, 2015, a magnitude 7.8 earthquake struck central Nepal, causing more than 8,000 deaths throughout the country. Two weeks later, a magnitude 7.3 aftershock caused further damage and uncertainty.
Massive landslides wiped out entire villages, rivers were dammed by landslides, and the geologic and geomorphic integrity of high altitude mountains and glaciers was destabilized. Scientists worried that the seismic activity could also result in new glacial lake outburst floods (GLOFs) through the weakening of terminal moraines and destabilization of potential triggers, such as overhanging ice and landslides. It was also feared that the arrival of the monsoon rains could further destabilize mountainsides, hillslopes, and moraines through the continuous soaking rains, melting of ice, and saturation of soils.
Miraculously, only one of Nepal’s 21 potentially dangerous glacial lakes burst out during the earthquake, possibly related to the fact that most were all frozen at the time. However, in order to fully understand what the impacts of the earthquake were on lake stability, the High Mountains Adaptation Partnership fielded a volunteer group of U.S. and Nepali scientists and researchers to conduct detailed remote sensing and field-based assessments of three of Nepal’s most dangerous glacial lakes—Imja Lake (in the Mt. Everest region), Tsho Rolpa Lake (Rowaling region), and Thulagi Lake (Manaslu region). Field costs were funded by USAID’s Climate Change Resilient Development project with co-financing from the American Society of Civil Engineers, The University of Texas at Austin, Xylem Inc., and US21 Inc.
Imja, Tsho Rolpa, and Thulagi glacial lakes were chosen for detailed post-earthquake assessment because they were of immediate concern to Nepal’s Department of Hydrology and Meteorology, primarily because of their ranking as high risk lakes susceptible to flooding as a result of earthquakes, dam collapse, or other triggers. Secondly, additional concern was expressed over the fact that all three contain either significant downstream populations and/or infrastructure (e.g., hydropower plants) that would be severely damaged and/or destroyed in the event of a GLOF. Thirdly, Imja, Tsho Rolpa, and Thulagi are the three most studied glacial lakes in Nepal, offering a solid set of baseline data for comparative analyses; and are also the three most recognized by the press and an understandably uneasy Nepalese public.
Each assessment was conducted with the active collaboration with the Government of Nepal, the International Centre for Integrated Mountain Development, Tribhuvan University of Nepal, and the U.S. Agency for International Development/Nepal. The lake surveyor team members included geographer Alton C. Byers, civil engineer Daene C. McKinney, hydrologist Elizabeth A. Byers, hydrologist Ram Kumar Kapair, geologists Prakash Pokhrel and Pushpa Raj Dahal, and photographer Daniel A. Byers.
The final report, Post-Earthquake Assessment: Imja, Tsho Rolpa, and Thulagi Glacial Lakes in Nepal, is now available at: http://www.ccrdproject.com/high-mountains-adaptation-partnership/nepal-earthquake-survey-2015.
The report concludes that the earthquake and aftershocks caused an increase in the destabilization of the lakes. This deterioration comes on top of the ongoing destabilization caused by climate change in Nepal, which the team felt has entered an era of accelerated instability that will include increases in the number of landslides, floods, avalanches, and rockfall.
“Increases in the number, frequency, and magnitude of GLOFs can be expected with confidence,” said Byers, who led the assessment team in Nepal. “The April 25 earthquake and aftershock further destabilized the already deteriorating terminal/lateral moraines of all three lakes through the creation of massive cracks, shifted boulders, avalanche tracks, and impacts on their outlet channels.”
Through interviews and discussions, the team also found that communities downstream of the lakes are terrified over the likelihood of new GLOFs occurring in the near future, but that they lack adequate information about existing or planned early warning systems, lake risk reduction methods, and disaster management planning.
“There’s no need to wait until people are killed and millions of dollars of infrastructure are destroyed to start doing something,” said Dr. Byers. “Peru was confronted with the same problem in the 1940s, and yet managed to lower 35 of its dangerous glacial lakes from the 1950s onward. There hasn’t been a single GLOF-related fatality since in Peru, and we need to start developing similar methods for Nepal to do the same now.”
The report recommends the immediate survey of all 21 of Nepal’s dangerous lakes; the development of Nepal-specific risk reduction early warning system and lake lowering engineering methods; the strengthening of downstream community disaster management planning; and strengthening of Nepal’s glacial lake analysis and risk reduction capacities.