After Central, Now Eastern Himalayas? Glacial Lake Outburst In North Sikkim Sparks Alert Across The State

Relevance: GS1 - Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc GS3 - Disaster and disaster management.

(Source: Down to Earth, 10/04/2023)

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Why in the news?

• Recently, a sudden glacial lake outburst took place in Chungthang in northern Sikkim leading to a rise in water level in the River Teesta.
• Glaciers are retreating due to climate change. The increase in the anthropogenic footprint in the glaciers leads to the increasing threat of GLOFs, and over 200 glaciers in the Himalayas are vulnerable to outbursts.
• A Glacial Lake Outburst Flood on October 4th, 2023 which originated from portions of the Lhonak Lake in the Mangan District of North Sikkim has resulted in a catastrophic rise in the water levels and velocity downstream along the Teesta River Basin.
• It resulted in a sudden surge of water, with velocities going as high as 15 meters per second.
• A flash flood alert was issued in Sikkim after a cloud burst took place in Singtam.
• The State Disaster Response Force (SDRF) teams from the State Home Guard and Civil Defence and National Disaster Response Force (NDRF) have been deployed.

Impact

• The Chungthang Dam was damaged leading to rise in the Teesta’s water levels and the closure of the Sikkim-Kalimpong road.
• Transportation was disrupted by damage to the Phidang Bridge in Lower Dzongu and the Toong Bridge in Munthan.
• Flooding has affected various areas, with residents in low-lying regions, such as Singtam and Rangpo advised to relocate.

What is a Glacial Lake Outburst Flood?

• These floods are typically triggered by the rapid melting of glaciers, heavy precipitation, or the inflow of meltwater. In February 2021, Chamoli district in Uttarakhand experienced flash floods suspected to have been caused by GLOFs.
• GLOFs are generally caused by
  • rapid melting of glaciers
  • heavy precipitation
  • inflow of meltwater.
• According to a study published in Nature in February, around 15 million people across the world are at risk of sudden and deadly flooding from glacial lakes, which are expanding and rising in numbers due to global warming.
  • India, Pakistan, Peru, and China account for more than half of the people at risk.
• Previous instance: In 2013, flash floods occurred in Uttarakhand as a result of heavy rainfall and a GLOF caused by the Chorabari Tal glacial lake which resulted in the death of thousands and extensive infrastructural and property damage

How can GLOFs be mitigated?

• Identification of at-risk lakes: The government must identify hazardous lakes through field observations, and an analysis of historical records, geomorphological and geotechnical features, and other physical conditions.
• Adoption of Technology: Synthetic-Aperture Radar (SAR) imagery can automatically detect changes in water bodies such as the formation of new lakes during the monsoon season.
• Channeling Potential Floods: Controlled methods such as breaching, pumping, siphoning, or creating tunnels through moraine barriers or under ice dams will help reduce the volume of water in glacial lakes.
  • A terminal moraine creates a barrier which traps water in a glacial lake, which is called a moraine-dammed lake.
• Uniform Construction Codes: The government must formulate comprehensive guidelines for infrastructure development, construction, and excavation in vulnerable areas.
  • It must also create a proper framework for land-use planning procedures in GLOF-prone regions.
• Early Warning Systems (EWS): Expansion and improvement of the early warning systems for GLOFs in use to a global standard.
  • In some Himalayan regions, sensor- and monitoring-based technical systems have been implemented to provide early warnings.
• Human resource capacity building: Local communities play a major role in search and rescue, as well as conservation efforts which must be recognized and tapped by the government.
  • Over 80% of search and rescue operations are often carried out by local communities before official intervention.
  • The NDMA has recommended training local personnel in disaster response activities in order to ensure lower casualties.
• Comprehensive alarm systems: Alarm infrastructure can be modernized by incorporating technologies like smartphones and social media to complement traditional siren-based alarms.
• Rehabilitation: Existing infrastructure and human populations, including illegal habitations must be relocated from at-risk riparian basins.

River Teesta The Teesta River is a 414 km long major right-bank tributary of the Brahmaputra that flows through India and Bangladesh. Origin: It originates in the Himalayas near the Tso Lhamo Lake, in Sikkim. The Pahurni Glacier, Khangse Glacier, and ChhoLhamo Lake are also considered sources of the river. Route: It flows through Sikkim to the south into West Bengal before entering Bangladesh. It joins the Brahmaputra in Bangladesh and the Ganga and Meghana before flowing into the Bay of Bengal. Originally it emptied directly into the Padma River but changed course after 1787 to meet the Jamuna (as Bhramaputra is known in Bangladesh). River basin: The river basin extends from Sikkim in the eastern Himalayas, through West Bengal to the northern Rangpur division in Bangladesh. 83% of the river basin lies in India and the remaining 17% of it is in Bangladesh. It is home to around 30 million people, most of whom live in the Bangladesh region. The northern parts of the river basin are dry and cold while the southern and middle parts are hot, humid, and wet. Barrages: Two major large barrages have been constructed on the River Teesta at Gajoldoba in West Bengal and Duani in Bangladesh. Tributaries: Left-bank: Lachung Chhu, Chakung Chhu, Dik Chhu, Rani Khola, and Rangpo Chhu. Right-bank: Zemu Chhu, Rangyong Chhu and Rangeet River. Characteristics: The Teesta River is characterized by heavy rainfall and floods in the monsoon season. In north Sikkim which has steep and uneven terrain, extreme rainfall leads to slope transformation, landslides, etc, and deposits suspended sediments in the river channel. The Upper Teesta River basin: Glacial, accumulation of debris, debris avalanches, and rock glaciers. Middle and Lower Teesta River basin: Less slope and relatively subdued relief. The Teesta and its tributaries generally flow with high velocity and turbulent flow and carry boulders and suspended sediments. Temperatures are sub-zero in winter but rise to around 20 °C in summer in the upper part of the basin. Significance: Bangladesh: Its flood plain covers about 14% of the total cropped area of Bangladesh and provides direct livelihood opportunities to 73% of its population. West Bengal: Teesta is the lifeline of North Bengal with around 6 districts almost dependent on it for water. Dispute: Bangladesh claims 50% of the water between December and May every year as water flow to the country drops drastically during this time. However, this request has been opposed by West Bengal. To know more, click the link.

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FAQs

MCQs

Question: With reference to river Teesta, consider the following statements:

1. The source of river Teesta is the same as that of Brahmaputra but it flows through Sikkim.
2. River Rangeet originates in Sikkim and is a tributary of river Teesta.
3. River Teesta flows into the Bay of Bengal on the border of India and Bangladesh.

Which of the statements given above is/are correct? (UPSC CSE 2017)

(a) 1 and 3 only

(b) 2 only

(c) 2 and 3 only

(d) 1, 2 and 3