Post-earthquake assessment : Imja, Tsho Rolpa, and Thulagi glacial lakes in Nepal

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 throughout the world began to worry 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. 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 (www.highmountains.org) 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.