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Glacial lake outburst flood (GLOF)


At least 10 people have been killed and 80, including 23 Army personnel, are missing in Sikkim after the South Lhonak Lake – a glacial lake situated in the state’s northwest at 17,000 ft – burst due to incessant rains. This resulted in the rise of water levels in (downstream areas) Teesta River that caused flash floods at least in four districts of Sikkim (Mangan, Gangtok, Pakyong and Namchi).


GS I: Geography

Dimensions of the Article:

  1. Glacial Lakes
  2. Causes Behind GLOF
  3. Factors Making South Lhonak Lake Susceptible to GLOF
  4. Actions Taken by the Sikkim Government to Address South Lhonak Lake Expansion

Glacial Lakes

  • Glacial lakes, exemplified by South Lhonak Lake, are expansive bodies of water situated in proximity to, on top of, or beneath a melting glacier.
  • These lakes, as they expand, become progressively hazardous due to their containment by unstable ice or sediment comprising loose rock and debris.
  • A breach in the boundary surrounding these lakes can result in the rapid release of vast volumes of water down mountain slopes, leading to downstream flooding, an event termed as a glacial lake outburst flood (GLOF).

Causes Behind GLOF

Triggering Factors

  • GLOFs can be precipitated by various factors, including seismic activity such as earthquakes, extraordinarily heavy rainfall, and ice avalanches.
  • Given their typical presence in steep, mountainous terrains, occurrences like landslides or ice avalanches have the potential to directly impact these lakes.
  • The result is the displacement of water, causing it to surpass the natural dam and inundate areas downstream.

Notable Incident

  • In 2013, a catastrophic event unfolded in Uttarakhand’s Kedarnath region, marked by flash floods and a consequential GLOF.
  • The Chorabari Tal glacial lake was responsible for this incident, resulting in the loss of thousands of lives.

Factors Making South Lhonak Lake Susceptible to GLOF

  • Rapid Glacier Melting
    • The accelerated melting of glaciers in the Sikkim Himalayan region, primarily due to rising global temperatures, has led to the formation of numerous glacier lakes and the expansion of existing ones, including South Lhonak Lake.
  • High Number of Glacier Lakes
    • According to the Sikkim State Disaster Management Authority (SDMA), there are currently over 300 glacial lakes in the Sikkim Himalayan region, with 10, including South Lhonak Lake, identified as vulnerable to outburst floods.
  • Significant Growth in Lake Size
    • South Lhonak Lake and its parent glacier, Lhonak, have experienced substantial growth, with South Lhonak expanding nearly 2.5 times its size since 1989.
  • Earthquake Activity
    • Earthquake events, such as a magnitude 4.9 earthquake in 1991 near the glacier feeding South Lhonak Lake and a more recent earthquake in 2011 with a magnitude of 6.9, may have weakened the boundaries of the lake.
  • Impact of Heavy Rainfall
    • Continuous heavy rainfall has further exacerbated the situation, contributing to the lake’s bursting.

Actions Taken by the Sikkim Government to Address South Lhonak Lake Expansion

Government Oversight

  • South Lhonak Lake has been under continuous observation by government authorities.

Siphoning Off Water

  • In 2016, a collaborative effort involving members of the Sikkim SDMA, Sikkim’s Department of Science and Technology, and Climate Change led to the implementation of a technique to syphon off water from South Lhonak Lake.
  • This process was executed under the guidance of innovator Sonam Wangchuk.
  • Authorities installed three 8-inch wide and 130-140 meters long High-Density Polyethylene (HDPE) pipes, enabling the extraction of 150 liters of water per second from the lake.

-Source: Indian Express

December 2023