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.