GLACIAL LAKE OUTBURST FLOOD (GLOF)
1. Context
Recently, At least five persons died and 42 people, including 22 Army personnel, went missing after heavy rainfall triggered a lake outburst in parts of the highly vulnerable Lhonak Lake in north Sikkim and resulted in a flash flood in the Teesta river basin, officials said. They said a search operation was on to trace those missing.
2. About glacial lake outburst flood (GLOF)
- A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake.
- An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a jokulhlaup.
- The dam can consist of glacier ice or a terminal moraine. Failure can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, volcanic eruptions under the ice, or massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.
3. About flash flooding
- Flash flooding is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions.
- It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice or snow flowing over ice sheets or snowfields.
- Flash floods may also occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam, as occurred before the Johnstown Flood of 1889.
- Flash floods are distinguished from regular floods by having a timescale of fewer than six hours between rainfall and the onset of flooding.
3.1. The reason for flash floods
There are several reasons why flash floods can occur, but the most common cause is heavy rainfall. When rain falls too quickly for the ground to absorb it, the water can run off and cause flooding. Flash floods can also be caused by:
- Thunderstorms can produce heavy rainfall, especially slow-moving or stationary thunderstorms.
- Hurricanes and tropical storms can produce heavy rainfall and storm surge, which can lead to flash flooding.
- If a dam or levee fails, it can release a large amount of water that can cause flash flooding downstream.
- Ice jams can form when large chunks of ice break off from a glacier or river and jam together. This can block the flow of water and cause flooding upstream.
- Landslides can block rivers and streams, causing flash flooding downstream.
- Vegetation helps slow the water flow and allows it to infiltrate the ground more easily. Areas with little or no vegetation are more likely to experience flash flooding.
- Urban areas are more likely to experience flash flooding than rural areas. This is because pavement and other impervious surfaces prevent water from infiltrating the ground.
4. How did South Lhonak Lake become susceptible to GLOF?
In 2021, a study published in the journal Geomorphology warned that the lake was at risk of a catastrophic GLOF. The study also found that the lake's water volume had increased by 74% since 1962. South Lhonak Lake in Sikkim, India, has become susceptible to GLOF due to several factors, including:
- Climate change is causing glaciers in the Himalayas to melt at an accelerated rate. This is leading to the formation of new glacial lakes and the expansion of existing ones, such as South Lhonak Lake.
- South Lhonak Lake is located in a steep-sided valley with a narrow outlet. This makes it difficult for water to drain from the lake, increasing the risk of a GLOF.
- South Lhonak Lake is dammed by a moraine, which is a pile of loose rocks and debris.
- Moraines are naturally unstable and can be easily breached by heavy rainfall, earthquakes, or other triggers.
- South Lhonak Lake is a relatively deep lake, with a maximum depth of over 100 meters.
- This means that a large volume of water could be released quickly if the lake dam were to breach.
- South Lhonak Lake is also located in a seismically active region. Earthquakes can destabilize the moraine dam and trigger a GLOF.
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Image Source: Research Gate
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For Prelims: South Lhonak Lake, Flash Flooding, Glaciers, Glacial Lake Outburst Flood, Sikkam, Climate Change, Teesta River,
For Mains:
1. Describe the environmental and socio-economic impacts of flash floods. How can early warning systems and disaster preparedness help mitigate the risks associated with flash floods? (250 Words)
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Previous Year Questions
1. On the planet earth, most of the freshwater exists as ice caps and glaciers. Out of the remaining freshwater, the largest proportion (UPSC 2013) (a) is found in the atmosphere as moisture and clouds (b) is found in freshwater lakes and rivers (c) exists as groundwater (d) exists as soil moisture Answer: C 2. Consider the following pairs: (UPSC CSE 2019)
Glacier River
1. Bandarpunch Yamuna
2. Bara Shigri Chenab
3. Milam Mandakini
4. Siachen Nubra
5. Zemu Manas
Which of the pairs given above are correctly matched?
A. 1, 2 and 4 B. 1, 3 and 4 C. 2 and 5 D. 3 and 5
Answer: A
3. Consider the following features related to a glacial lake outburst flood (GLOF): (UGC NET Geography 2019)
a. Involves sudden release of meltwater
b. Failure of moraine and ice dam
c. Large downstream discharge causing floods
d. Rapid event casting for few seconds
Select the correct answer from the options given below:
A. (a) and (b) are correct
B. (c) and (d) are correct
C. (a), (b) and (c) are correct
D. (b), (c) and (d) are correct
Answer: C
4. With reference to the Agreement at the UNFCCC Meeting in Paris in 2015, which of the following statements is/are correct? (UPSC 2016)
1. The Agreement was signed by all the member countries of the UN and it will go into effect in 2017
2. The Agreement aims to limit greenhouse gas emissions so that the rise in average global temperature by the end of this century does not exceed 2°C or even 1.5°C above pre-industrial levels.
3. Developed countries acknowledged their historical responsibility in global warming and committed to donate $ 1000 billion a year from 2020 to help developing countries to cope with climate change.
Select the correct answer using the code given below:
A. 1 and 3 only B. 2 only C. 2 and 3 only D. 1, 2 and 3
Answer: B
5. A new type of El Nino called El Nino Modoki appeared in the news. In this context, consider the following statements: (UPSC 2010)
1. Normal El Nino forms in the Central Pacific ocean whereas El Nino Modoki forms in the Eastern Pacific ocean.
2. Normal El Nino results in diminished hurricanes in the Atlantic ocean but El Nino Modoki results in a greater number of hurricanes with greater frequency.
Which of the statements given above is/are correct?
A. 1 only B. 2 only C. Both 1 and 2 D. Neither 1 nor 2
Answer: B
6. La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino? (UPSC 2011)
1. La Nina is characterized by unusually cold ocean temperature in the equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.
2. El Nino has an adverse effect on the south-west monsoon of India, but La Nina has no effect on the monsoon climate.
Which of the statements given above is/are correct?
A. 1 only B. 2 only C. Both 1 and 2 D. Neither 1 nor 2
Answer: D
7. Consider the following statements: (MPSC 2017)
a. La Nina is a little girl.
b. During the time of La Nina cold water in the ocean rises to the surface.
c. La Nina strengthens the Indian monsoon.
d. During the time of El Nino, trade winds weaken, and warm water moves east in the ocean. Which of the above statements is/are correct?
A. Only a and b B. a, b and c C. Only b and c D. All of the above
Answer: D
8. With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (UPSC 2020)
1. OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January-March.
2. OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.
Select the correct answer using the code given below:
A. 1 only B. 2 only C. Both 1 and 2 D. Neither 1 nor 2
Answer: B
9. With reference to 'Indian Ocean Dipole (IOD)' sometimes mentioned in the news while forecasting Indian monsoon which of the following statements is/are correct? (UPSC 2017)
1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an EI Nino's impact on the monsoon.
Select the correct answer using the code given below:
A. 1 only B. 2 only C. Both 1 and 2 D. Neither 1 nor 2
Answer: B
10. "EL Nino" refers to a temperature anomaly in the ________ ocean. (NTPC 2017)
A. Indian B. Pacific C. Southern D. Atlantic
Answer: B
11. The Ministry of Environment, Forest and Climate Change recently published the draft Environment Impact Assessment (EIA) Notification, in 2020. Which of the following statements is correct about EIA? (Punjab Civil Service 2020)
1. It predicts the effect of a proposed industrial/infrastructural project on the environment.
2. It prevents the proposed activity/project from being approved without proper oversight or taking adverse consequences into account.
3. It compares various alternatives for a project and seeks to identify the one which represents the best combination of economic and environmental costs and benefits.
4. As per the new notification, Coal and non-Coal mineral prospecting and solar photovoltaic projects do not need prior environmental clearance.
Select the correct answer using the code given below:
A. Only 1 and 2
B. Only 2, 3 and 4
C. Only 1, 2 and 3
D. Only 1, 2 and 4
Answer: D
12. In the context of India’s preparation for Climate -Smart Agriculture, consider the following statements: (UPSC 2021)
1. The ‘Climate-Smart Village’ approach in India is part of a project led by the Climate Change, Agriculture and Food Security (CCAFS), an international research program.
2. The project of CCAFS is carried out under the Consultative Group on International Agricultural (CGIAR) headquartered in France.
3. The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India is one of the CGIAR’s research centers.
Which of the statements given above is correct?
(a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Answer: D
13. Consider the following statements: (UPSC 2017)
1. In India, the Himalayas are spread over five States only.
2. Western Ghats are spread over five States only.
3. Pulicat Lake is spread over two States only.
Which of the statements given above is/are correct?
A. 1 and 2 only B. 3 only C. 2 and 3 only D. 1 and 3 only
Answer: B
14. Which of the following statements in respect of landslides are correct? (NDA 2022) 1. These occur only on gentle slopes during rain.
2. They generally occur in clay-rich soil.
3. Earthquakes trigger landslides.
Select the correct answer using the code given below. A. 1 and 2 B. 2 and 3 C. 1 and 3 D. 1, 2 and 3 Answer: B 15. With reference to River Teesta, consider the following statements: (UPSC 2017)
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 16. Teesta River is the tributary of _______. (Kerala PSC Secretariat Assistant 2018) A. Ganga B. Yamuna C. Brahmaputra D. Narmada Answer: C Mains 1.Describe the various causes and the effects of landslides. Mention the important components of the National Landslide Risk Management Strategy. (2021, GS3)
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Source: indianexpress
