Glacial Lake Outburst Flood

A glacial lake outburst flood, or GLOF, is sudden release of water from a lake fed by glacier melt that has formed at the side, in front, within, beneath or on the surface of a glacier. It can be impounded by moraine complexes, glacial ice or even bedrock and, as a result of breaching, slope failure, overtopping or other failure mechanisms, lead to catastrophic phenomena in the high mountains that threaten people’s lives, livelihoods and regional infrastructure.

In the Hindu Kush Himalaya, moraine-dammed glacial lakes are common and numerous GLOF events have been traced back to the failure of moraine dams. A moraine-dammed lake forms as a glacier retreats, and meltwater fills the space between the proglacial moraine (in front of the glacier) and the retreating glacier. As the volume of the glacial lake grows, so does the pressure on the dam containing it. Fragmentation of the source glacier, landslides and other processes can trigger displacement waves in the lake, potentially compromising the stability of the dam and resulting in a GLOF. Failure of the dam can also occur due to internal processes, such as water seeping through the structure.

Although GLOFs are not a recent phenomenon in the HKH, they remain a persistent threat to downstream communities and infrastructure and must therefore be part of any planning in the lower reaches. The frequency of GLOFs and risk from potential GLOFs are expected to increase as the climate continues to change. As temperatures rise, new lakes form, existing ones expand and sometimes merge, increasing the potential flood volumes in the high mountains.

In 2018, ICIMOD released a report on the status of glacial lakes in the HKH that mapped and classified more than 25,000 glacial lakes in the five major river basins spread across the region.  8.3% of the glacial lakes are located below 4000 masl.

There is still a lot that we do not know about the dynamics of glaciers and glacial lakes in the Hindu Kush Himalaya. It is, therefore, important to learn as much as possible about past events and the dynamics behind them and to assess the overall GLOF risk in the region for better planning and implementation of disaster risk reduction measures and climate change adaptation in the region.