Langmale Glacier (source: Alton Byers).
On May 2, Daene McKinney, Dhananjay Regmi and Alton Byers flew from Dingboche over the Sherpani Col and into the upper Barun valley in the eastern Himalayas of Nepal in an effort to determine the source of an April 20 flood.
Dorje Sherpa, a resident of Yangle Kharka, reported that the lake burst around 1 p.m., flooding down the Barun River, and reached his village about a half-hour later. The settlements of Langmale, Zak Kharka and Rephuk Kharka remained largely undamaged, as did lodges in the area, but Yangle Kharka suffered a loss of at least three buildings and many hectares of valuable grazing land. Tematang, further downstream, is located on a high terrace and was fortunately spared damage. However, all local bridges were washed away.
The flood arrived at the confluence of the Barun and Arun Rivers around 4 p.m., where the debris dammed the Arun River, forming a temporary lake 2-3 km long. This setting is remote, a two-day walk from the district capital of Khandbari. The lake presented a serious threat, since it would have created a second, more destructive flood in the densely populated areas downstream had it breached the dam.
The government response was swift. Police reached the site on the morning of April 21 and started to plan how to protect the endangered communities. Deputy Prime Minister and Minister for Home Affairs Bimalendra Nidhi issued a directive to open the dam in order to reduce the threat of flooding. The Natural Disaster Rescue Committee, an organization within the Nepali Ministry of Home Affairs, met in Kathmandu to discuss the situation. Fortunately, the lake began to drain spontaneously around 2 p.m. on April 21, with some local flooding below, but far less than was feared.
Rather than originating in the Lower Barun glacial lake or as a result of heavy rains and flooded tributaries, as some surmised, the flood’s trigger appears to have been two surficial glacial lakes on the Langmale Glacier just east of the Langmale settlement area, most likely supplemented by englacial conduit and subglacial conduit, as in the Lhotse glacier flood Byers observed and recorded last June. The combined volume of water cascaded over the Langmale’s terminal moraine, creating a huge torrent that picked up more material and debris as it cascaded down the Barun River channel, carving out massive new river channels and flooding large areas of grazing and forest land.
Regmi and Byers spoke with 16 villagers in Yangle Kharka, who said that they would be rebuilding them and returning home soon. The villagers expressed deep concern about the impacts of the flood on the coming tourist season. The damaged trails and bridges make it difficult for local porters and foreign trekkers to reach the region, and the dramatically changed landscapes, with landslide scars, are less visually appealing to tourists.
McKinney, Regmi and Byers were only able to fly another 10 km or so down valley because of fuel shortages before returning to the upper Barun and Khumbu, but they noticed another very large and fresh torrent scar on the right bank of the Barun. They plan to study it as well and learn more about its possible role in the accumulation of debris and creation of the lake. Through this research, they hope to contribute to the active discussion of glacier hazard mitigation in Nepal and other mountain regions in the Himalayas and around the world.