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Disaster in Sikkim: What led to Glacial Lake Outburst?


  • Sikkim experienced a cloudburst over South Lhonak Lake followed by outburst of severe floods in which caused casualties and displacements in the state.
  • The main districts affected due to Sikkim floods are Mangan, Gangtok, Pakyong and Namchi.

What have triggered Sikkim Floods:-

Glacial Lake Outburst Flood (GLOF):

  • The primary reason for the sudden surge in water level could be combination of excess rainfall and a Glacial Lake Outburst Flood event at South Lhonak Lake.
  • The lake outburst caused arise in water levels with high velocities crossing the danger levels.
  • These glacial lakes are mostly dammed by unstable ice or sediment composed of loose rock and debris, hence, become more dangerous as they grow bigger.
  • A breach in lake wall results in flowing of large amounts of lake water down the mountains.
  • The GLOF led to the Teesta river spilling over its banks in at least four districts.
  • The GLOF can be triggered by several reasons, like earthquakes, heavy rains or ice avalanches.

  • Hence, scientists are exploring that the strong earthquake that struck Nepal and surrounding region on Tuesday could be responsible for South Lhonak Lake outburst.
  • The lake was already vulnerable and covered an area of 168 hectares. It has now  reduced to 60 hectares, indicating that about 100 hectares of water volume has breached the level.

Melting of Glaciers:

  • With rising global temperatures, glaciers in Sikkim Himalayas have been melting, giving rise to many glaciers lakes and expanding existing lakes in the region.
  • Lhonak lake has grown 1.5 times and South Lhonak lake nearly 2.5 times of their initial size.
  • This lake is one of the 14 potentially dangerous lakes susceptible to GLOF.
  • The associated South Lhonak Glacier is melting in abnormal manner, which results in accumulation of additional water in these lakes, along with water of North Lhonak and Main Lhonak glaciers.
  • In such case, the GLOFs could occur easily and claim lives and damage assets 10 km downstream.
Source - Indian Express

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