Glacial lake outburst floods occur when a lake (water body) is fed by glacial melt that has

formed along the side, in front, within breadth, or on the surface of the glacier suddenly

releases water. Moraine complexes, glacial ice, and even bedrock can contain it.

• The significant flooding caused by glacial lake outbursts in high mountains poses a threat to people’s lives, livelihoods, and regional infrastructure and is caused by breaching, slope failure, overtopping, and other causes.
• Fragmentation of the glacier source, landslides, and other processes might also destabilise the lake, causing an outburst of flood and jeopardising the dam. Furthermore, the dam may break as a result of internal processes such as water seepage through it.

Glacial lake outbursts have three main characteristics, which are as follows:

• There is a sudden release of water.
• The events last from a few hours to a few days and are generally rapid in nature.
• They discharge large amounts of water into downstream rivers.

Causes of Glacial Lake Outburst Flood:

• Erosion, accumulation of water pressure, rapid slope movement into the lake, etc.
• Heavy rainfall and melting of snow.
• Processes that run in a loop (flood from a lake situated upstream).
• Under the ice or beneath the ice, volcanic eruptions or earthquakes may occur.
• The dam was formed as a result of ice melting.
• Subsurface outflow tunnels are being obstructed (applies only to lakes without surface outflow or lakes with a combination of surface and subsurface outflow).
• Degradation of dams over time.
• Displacement of water as a substantial part of an adjacent glacier collapses into a glacial lake.

Glacial Lake Outburst Event in India:

• Flash floods caused by glacial lake overflow hit the Chamoli district in Uttarakhand in February 2021. The Kedarnath tragedy in 2013 was associated with glacial lake breaches as well.
• Over 5,000 glacier lakes have formed in the Himalayas from glacier melt, which is creating moraine dams. These dams are potentially unstable, so their failure can have catastrophic societal and geomorphic impacts.
• According to the National Disaster Management Authority (NDMA), glacial retreat caused by climate change has resulted in the formation of numerous new glacial lakes in most parts of the Hindu Kush Himalaya, which is the major cause of GLOFs. Glacial lakes in the Himalayas are expanding during this retreating glacier era, posing a hazard to downstream infrastructure and life.