Context:
A cloudburst over Lhonak Lake in north Sikkim triggered a flash flood in the Teesta River basin.
News Highlights:
- Lhonak Lake is a glacial lake
- Location – Sikkim
- Lake outburst resulted in the breach of the Chungthang dam (State’s largest hydropower project)
- Other important lakes in Sikkim – Cholamu Lake (highest lake in India), Gurudongmar Lake.
About Teesta River:
- A tributary of the Brahmaputra River (Jamuna in Bangladesh)
- Source – Pahunri glacier
- Basin States – Sikkim (72.43%)and West Bengal (27.57%)
- Left-bank Tributaries – Lachung Chhu, Chakung Chhu, Dik Chhu, Rani Khola, Rangpo Chhu
- Right-bank Tributaries – Zemu Chhu, Rangyong Chhu, Rangeet River
Geographical Concepts
What is a cloudburst?
- India Meteorological Department (IMD) defines it as unexpected precipitation that happens in a short period exceeding 100 mm per hour over a geographical region of approximately 20 to 30 square km.
What is GLOF?
- Glacial lakes are large water bodies positioned in front of, on, or beneath melting glaciers.
- Their increasing size poses greater risks, as these lakes are typically impeded by unstable ice or sediment made up of loose rocks and debris.
- If their boundaries rupture, significant volumes of water can surge down mountainsides, potentially resulting in downstream flooding.
- The vulnerability of these lakes lies in their proximity to glaciers and the potential for abrupt releases of water.
- Causes – earthquakes, extremely heavy rains and ice avalanches etc.
How did South Lhonak Lake become susceptible to GLOF?
- With the rising global temperatures, glaciers in Sikkim Himalayan have been melting rapidly, giving rise to many glacier lakes and expanding the already existing ones (such as Lhonak Lake) in the region.
Flash floods are brief, powerful floods that occur less than 6 hours of heavy rainfall in a highly localized area.
Previous Year 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 it 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?
(a) 1 and 3 only
(b) 2 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (b)
Explanation:
Teesta River originates from the Pahunri glacier (not from the same source as the Brahmaputra). Hence, statement 1 is not correct.
Before going to the Bay of Bengal through Bangladesh Teesta flows through West Bengal and Sikkim. Hence, statement 3 is not correct.
