Sikkim Flash Floods

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October 06, 2023

Why in news?

A cloud burst over Lhonak Lake in North Sikkim resulted in a flash flood in the Teesta River in Lachen Valley killing around 14 people.

South Lhonak Lake

  • Location- Located at 17100 feet above sea level in Sikkim
  • Formation- It is a glacial moraine dammed lake formed due to the melting of the Lhonak glacier.
  • It is one of the 14 potential lakes susceptible to Glacial Lake Outburst Flood (GLOF).
  • Scientists had warned in 2021 that the South Lhonak lake in Sikkim would burst.


What triggered Sikkim floods?

  • GLOF & excess rainfall - The primary reason for sudden surge in water level appears to be a likely combination of excess rainfall and a Glacial Lake Outburst Flood (GLOF) at South Lhonak Lake.
  • Rough weather - According to National Disaster Management Authority (NDMA), out of the 7500 glacial lakes in the Himalayan ranges, Sikkim has 10% of it.
  • Further, this region is known for highly localised heavy rainfall events.
  • Melting of glaciers The lake is rapidly growing in size due to the melting of Lhonak glaciers.
  • GLOFs occur when lakes formed by melting glaciers suddenly burst open.
  • Nepal earthquake - Scientists are also exploring whether the recent earthquake that struck Nepal is responsible for the south Lhonak lake outburst.

A flash flood is a sudden flood of water that occurs within a short frame of time after a precipitation event, which is generally less than 6 hours.

What are Glacial Lake Outburst Flood (GLOF)?

  • Glacial lakes- They are large bodies of water that sit in front of, on top of, or beneath a melting glacier.
    • Example - Uttarakhand’s Kedarnath witnessed flash floods along with a GLOF in 2013 caused by the Chorabari Tal glacial lake.
  • GLOF - Glacial lakes are mostly dammed by unstable ice or sediment composed of loose rock and debris.
  • If the boundary around them breaks, huge amounts of water rush down the mountains, causing flood in the downstream areas.​​​​​​​
  • It is fast, and can be triggered by various causes, including glacial melting, rising water levels, and earthquakes.


How much damage has been caused in Sikkim?

  • The lake outburst caused extensive damage to life and property, including the breakdown of road networks and communication.
  • The lake outburst led to the breach of the Chungthang dam, which is the largest hydropower project in the state.
    • Chungthang dam is also a part of the 1,200-megawatt (MW) Teesta Stage III Hydro Electric Project.
  • Bridges such as the Indreni bridge, Ritchu Bridge, Sangkhalang bridge, etc. were washed away in the floods

What steps have been taken to prevent GLOFs?

  • The Sendai Framework (2015-2030) It is a global blueprint for disaster risk reduction and prevention.
  • Coalition for Disaster Resilient Infrastructure - CDRI is an international climate initiative by India in 2019 to promote resilient climate-proof critical infrastructure in member countries.
  • National Disaster Management Authority (NDMA) - NDMA, headed by the Prime Minister of India, is the apex body for Disaster Management in India.
  • Central Water Commission (CWC)/ National Remote Sensing Agency (NRSA)/ State governments also check for landslides and blockages in rivers with the help of satellite imageries.
  • Aapda Mitra – Launched in 2016, it is a central sector scheme implemented by NDMA to train community volunteers in disaster response in selected 30 most flood prone districts of 25 states including Sikkim.
  • Doppler radars - The India Meteorological Department (IMD) has been using Doppler radars, a flash floods forecasting and warning systems.
  • Sikkim State Disaster Management Authority (SSDMA)It is the nodal institution for planning, co-ordination and monitoring for disaster prevention, mitigation, preparedness and management in the State.
  • Flood Management Programme – Under the scheme, critical anti-erosion works have been undertaken in Ganga Basin, Brahmaputra and Barak Valley States.

What lies ahead?

  • As per the International Centre for Integrated Mountain Development (ICIMOD) report, the most important mitigation measure for reducing GLOF risk is to reduce the volume of water in the lake in order to reduce the peak surge discharge.
  •  In order to reduce the volume of lake water, the ICIMOD report recommended:
    • Controlled breaching
    • Construction of an outlet control structure
    • Pumping or siphoning out the water from the lake
    • Making a tunnel through the moraine barrier or under an ice dam

Teesta River

  • It is a major transboundary river that flows through India and Bangladesh.
  • It originates from the Pahunri (or Teesta Kangse) glacier and flows through Sikkim and West Bengal before flowing into Bangladesh.
  • It is a tributary of the Jamuna River (Brahmaputra River).



  1. Indian Express- Explained Glacial Lake Outburst Flood in Sikkim
  2. Down To Earth- Threat of South Lhonak Lake
  3. CNBC18 | Sikkim floods reason
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