Context: Recently, Chungthang dam of Sikkim has been collapsed due to the abrupt eruption of South Lhonak Lake, triggering a surge in water levels, within the Teesta river. 

• In response to this, the National Disaster Management Authority (NDMA) has planned to install early warning systems for real-time alerts at most of 56 at-risk glacial lakes in India.

What are the causes of disaster in Sikkim?

• The 3 main causes of disaster in Sikkim are- a cloud burst, a GLOF (Glacial Lake Outburst Flood), and the earthquakes in nearby regions. 

• Cloudburst is a sudden, very heavy rainfall, usually local in nature and of brief duration. 

• GLOF is a type of flood that occurs when a dam containing a glacial lake collapses.

• The glacial lakes, formed by the embankment of unstable moraines, can burst due to various triggers, including heavy rainfall, avalanches, rockfalls, landslides and earthquakes.

• Rising temperatures are contributing to climate change led extreme events, including melting of glaciers, which increases the chances of GLOF.

• GLOFs can be unpredictable when there is a lack of sufficient data on rainfall intensity, location of landslide, impounded volume, physical condition of lakes and water bodies. 

• The fragility of the Himalayan ecosystem is disturbed through hydropower and other dams.

• Any hydroelectric project situated downstream of unstable lakes are at the risk of being washed away, posing potential dangers to human lives

How was South Lhonak Lake formed?

• South Lhonak Lake is a moraine-dammed lake, that was formed due to the melting of the Lhonak glacier.

• Moraine is the accumulation of rock debris carried by glaciers or ice sheets.

• When these moraines accumulate at the glacier’s edge, marking its maximum extent, they create a terminal moraine.

• If a terminal moraine obstructs the outflow of meltwater from the valley, it forms a moraine-dammed lake.

How South Lhonak Lake poses danger?

• South Lhonak Lake is one of the rapidly expanding lakes in the Sikkim, and its growth is inversely related to the accelerated melting of the Lhonak glacier resulting from global warming.

• When the lake bursts, it releases a massive amount of water all at once, causing flash floods downstream. 

• The Himalayan region already has more pronounced geological activity, which may trigger its expansion.

What are the solutions to avoid such disasters in future?

• Reducing the number of large hydroelectric project in the fragile regions or the risk prone zones are the key to reduce similar potential disasters.

• This is despite the Sikkim having large potential for generating power by utilising the fast-flowing rivers in the Himalayan mountains.

• As global warming is causing glaciers to melt and increasing water pressure in glacial lakes, reducing the emission is one potential solution.

• Achieving net-zero emissions requires all governments to enhance their Nationally Determined Contributions and take immediate steps to reduce emissions.

• Controlled breaching of hazardous glacial lakes: An outflow channel can be excavated using explosives, which can erode the moraine wall, causing a fast lowering of the lake level.

• Pumping out the water from the lake: The use of a turbine, propelled by the water force at the outside of the moraine dam, will lower the energy costs.

• Making a tunnel through the moraine dam: Tunnelling can only be carried out through competent rock beneath or beside a moraine dam.

By ensuring the compliance with the Sendai Framework for Disaster Risk Reduction 2015-2030 to which India is a signatory-

• The Sendai Framework aims to achieve reduction of disaster risk and losses in lives, livelihoods and health and in the economic, physical, social, cultural and environmental assets of persons, businesses, communities and countries.

• It outlines 7 targets and 4 priorities for action to reduce existing disaster risks.

Other key facts

• Chungthang dam is situated at the confluence point for the Lachen River and the Lachung River, which together forms the Teesta River.

• Lachen River originates from the South Lhonak Lake.