GLACIAL LAKE OUTBURST FLOOD (GLOF)
This topic has relevance in the “Disaster Management” section of the UPSC CSE exam.
For Prelims:
What is Glacial Lake Outburst Flood (GLOF)?
For Mains:
GS3: Disaster Management
Why in the news?
The South Lhonak Lake in Sikkim burst recently, causing flash floods in North Sikkim. This glacial
lake, formed by the melting Lhonak glacier, has seen notable changes.
About Glacial Lake Outburst Flood (GLOF)
Glacial lakes are unique water bodies closely associated with melting glaciers. Due to their
unstable nature, these lakes can pose significant risks to the environment and human
settlements.
When a glacial lake experiences a sudden release of water, it results in a phenomenon known
as a Glacial Lake Outburst Flood (GLOF).
Glacial Lakes: Potential Time Bombs
Glacial lakes, such as the South Lhonak Lake, can take various forms, including sitting in front
of, on top of, or beneath a melting glacier. These bodies of water tend to expand over time as
glaciers melt, making them increasingly hazardous.
The main reason for this danger is that glacial lakes are typically dammed by unstable
materials like ice and sediment composed of loose rocks and debris.
When the boundary around these glacial lakes gives way, it can rapidly discharge immense
volumes of water cascading down the mountain slopes.
This sudden deluge can potentially cause extensive flooding in downstream areas, thereby
earning the name “Glacial Lake Outburst Flood” or GLOF.
Triggers for GLOF
GLOF events are not solely the result of natural glacial meltwater dynamics. Various factors can
trigger these devastating floods. Among the most prominent triggers are:
Earthquakes: Seismic activity can disrupt the fragile balance around glacial lakes, leading to
their sudden release of water. This can result in catastrophic flooding downstream.
Extreme Rainfall: Intense and prolonged rainfall in the region can contribute to the rapid
expansion of glacial lakes, increasing the risk of a GLOF event.
Ice Avalanches: In regions where glacial lakes are often nestled in steep, mountainous terrain,
ice avalanches can directly impact the lakes. When these avalanches displace water within the
lakes, it can overflow natural dams and cause downstream flooding.
The 2013 Uttarakhand Disaster
In 2013, the Kedarnath region in Uttarakhand, India, witnessed a devastating natural
disaster. Flash floods, coupled with a GLOF event triggered by the Chorabari Tal glacial lake,
claimed the lives of thousands of people.
This tragic incident serves as a stark reminder of the potential dangers of glacial lakes and
the importance of understanding and monitoring them in vulnerable regions.
More about South Lhonak Lake GLOF
Flash Floods Due to Heavy Rain: The South Lhonak Lake’s outburst was triggered by heavy
and relentless rainfall in the region, leading to flash flooding.
Impact on Teesta River and Districts: The lake’s outburst raised Teesta River’s water levels,
flooding four districts: Mangan, Gangtok, Pakyong, and Namchi. This event highlights the
downstream vulnerability to glacial lake outburst floods (GLOFs).
Monitoring and Environmental Changes: The Central Water Commission monitors the
South Lhonak Lake as one of eleven large glacial lakes. Notable environmental changes include:
Glacial Retreat: Over 29 years, the Lhonak glacier has shrunk from 6.4 km to 5.1 km, revealing
the impact of climate change.
Growing Lake: Starting at 0.17 sq km in 1977, the Lhonak lake expanded to 0.78 sq km in
2002 and 1.35 sq km in 2019. Recent growth, observed from September 17 to 28, added
roughly 5 hectares or around 3% to its size.
NDMA Guidelines on Risk Mitigation of GLOF:
Identifying and Mapping Dangerous Lakes: Guidelines recommend identifying and mapping
high-risk glacial lakes using field observations, historical data, and landscape features to assess
potential hazards.
Structural Measures: Preventing glacial dam breaches involves controlled breaching, water
pumping, or siphoning to reduce lake water volume, reducing the risk of GLOFs.
Early Warning Systems: Installing sensors and monitoring equipment helps detect changes in
water levels and temperature, enabling timely alerts and evacuation plans for at-risk
communities.
Capacity Building: Enhancing the readiness of local communities and authorities through
training in risk assessment, response planning, and search and rescue operations is vital for
GLOF preparedness.
Public Awareness: Creating awareness among vulnerable communities about GLOF risks and
safety measures through engagement programs and information campaigns is essential.
Research and Monitoring: Continuous research and monitoring of environmental changes,
glacial retreats, and new lake formations improve understanding and prediction of potential
GLOF events, aiding mitigation efforts.
Q1. With reference to the Glacial Lake Outburst Flood (GLOF), consider the following
statements:
1. Glacial lakes are typically dammed by stable materials like ice and sediment composed of loose
rocks and debris.
2. Seismic activity can disrupt the fragile balance around glacial lakes, leading to their sudden
release of water.
3. Intense and prolonged rainfall in the region can contribute to the rapid expansion of glacial
lakes, increasing the risk of a GLOF event.
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 3 only
(d) None
Answer: (b)
Q2. Consider the following:
1. Destruction of property and infrastructure
2. Spread of diseases
3. Creation of new glacial lakes
4. Improved irrigation systems
How many of the above are not correct potential consequences of a GLOF?
(a) Only one
(b) Only two
(c) Only three
(d) All Four
Answer: (c)
Q3. Explain the concept of Glacial Lake Outburst Flood (GLOF). Discuss the guidelines
provided by the National Disaster Management Authority (NDMA) to mitigate Glacial
Lake Outburst Floods (GLOFs) risks.
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