Powerful Glacial Lake Outburst Floods in the Himalayas

Glacial lake outburst floods (GLOFs) are sudden, fast flowing releases of glacial lake water that move downslope as a result of dam failures. Glacial lakes are either moraine-dammed or ice marginal-dammed. GLOFs are triggered by the buildup of water pressure, ice and rock avalanches, earthquakes, erosion, and other natural disruptions. As water rushes downslope, it picks up rock, mud, and debris, endangering people, infrastructure, fields and livestock in its path. Recent research, published in Landslides, provides new understanding of GLOFs by studying their trigger mechanisms and disaster impacts.

Peaks of the Upper Barun Valley, Nepal (Source: Roger Nix/Flickr).

The research group on the recent study, led by Alton Byers, reconstructed a destructive GLOF that occurred on 20 April 2017 in the Upper Barun Valley, Nepal. The Langmale GLOF, as it was called, was rebuilt using remote sensing, field measurements, modeling, personal testimony and video footage. Results revealed a peak velocity between 4 to 8 m/s, the scale of the flood channel, and sand/silt/clay discharge estimates.

Byers and his team discovered the GLOF was triggered by a massive rockfall from Saldim Peak, which led to a chain reaction of events. The rockfall forcefully hit an unnamed glacier hundreds of meters below. This resulted in an avalanche of snow and ice, plummeting down into Langmale glacial lake, causing a tsunami-like wave to form and topple over terminal and left lateral moraines. The enormous wave then tumbled downslope, causing immense damage and rearrangement of the local landscape, according to the researchers. The Langmale GLOF carved into the land, ripped vegetation from its roots, and carried boulders thousands of feet. Imagine a landscape which once supported local livelihoods, now covered with mud and debris.  

Upper Barun Valley, Nepal, where the results of the Langmale GLOF are visible on the lower left (Source: Roger Nix/Flickr).

Researchers like Byers who study GLOFs face substantial limitations due to the remoteness and harsh weather of high mountain regions. They also face difficulties in terms of financing their research projects. The Langmale GLOF research group was able to overcome these obstacles in order to analyze the source, cause, and impacts of the Upper Barun Valley GLOF event. The research group highlighted the growing necessity for the implementation of early warning systems and urged for increased risk management and field studies of GLOFs.

How GLOFs Impact Local People

Although GLOFs often take place in secluded mountain regions, local people are also affected. Fortunately, no one was injured or killed in the Langmale GLOF, but the researchers report that four community buildings and six bridges were demolished. In addition, agricultural land was completely covered and tourism to the Upper Barun Valley suffered.

The Langmale research group reported growing concerns of local people due to the danger posed by GLOFs and associated economic tolls. A YouTube video captured the Langmale GLOF, its sheer velocity, and the destructive aftermath.

“Settlements in the Himalayan region are mostly situated near to the river bank or within the high flood plain,” shared Finu Shrestha, a research associate at ICIMOD“Communities living downstream of a glacial lake are the first ones who get threatened and face the potential damage if a GLOF happens. GLOF events produce huge impacts in the downstream [area] causing loss of lives and livelihood, damage to the settlements, roads, tracks and trails, bridges (wooden, suspension, motorable and highway bridges), and hydropower projects,” she told GlacierHub. 

Glacial meltwater flowing through the snow in the Himalayas in the north Indian state of Uttarakhand (Source: Sharada Prasad CS/Creative Commons).

It is clear that humans are negatively impacted by GLOFs, but are humans impacting the frequency of GLOFs too?

The Langmale research group commented that hundreds of glacial lakes have formed in the Nepal Himalayas in recent decades due to the rapid glacial recession caused by the warming climate. An increase in glacial lakes could lead to increased frequency of GLOFs. Due to projected temperature increases, GLOF frequency is only expected to increase in upcoming decades, according to additional research published in Cryosphere.

 

A Visit to the Source of a Recent Glacier Flood in Nepal

Alton Byers discussed a recent glacier hazard in Nepal with GlacierHub. Byers is a senior research associate at the Institute of Arctic and Alpine Research at the University of Colorado and co-manager of High Mountains Adaptation Partnership (HiMAP). He has been recognized as an Explorer by National Geographic. The account below is based on interviews with Byers and emails from Dhananjay Regmi, a geographer at Tribhuvan University in Kathmandu.

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.

Debris below lake on Langmale Glacier (source: Alton Byers).

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.

Debris and scarring in Barun River valley (source: Alton Byers).

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.

Damage at Yangle Kharka (source: Alton Byers).

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.

Dhananjay Regmi interviewing a local resident at Yangle Kharka (source: Alton Byers).

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.