• The National Green Tribunal (NGT) has issued notice to the Centre and others in a matter regarding the rapid expansion of the Himalayan glacial lakes, raising concerns over the increasing risk of natural disasters.

• The NGT took suo motu cognisance of a news report showing about 10.81 per cent increase of the glacial lakes in the last 13 years due to the rising temperatures.

• According to the report, the melting of glaciers due to increase in temperature paved the way for larger glacial lakes, which held more water and, in turn, increased the risk of natural disasters like floods and landslides.

• A recent report by the Central Water Commission (CWC) has highlighted a significant expansion of glacial lakes in the Himalayan region, with an increase of 10.81 per cent in surface area from 2011 to 2024. The report also notes that the surface area of glacial lakes in India has increased by 33.7 per cent during the same period.

• The NGT noted the report had outlined the sudden growth of these lakes that posed a heightened risk of Glacial Lake Outburst Floods (GLOFs), which could be catastrophic for downstream communities, infrastructure, and biodiversity.

• The report identifies 67 lakes in India that have seen an increase of over 40 per cent in surface area, placing them in the high-risk category for potential GLOFs. 

• The most notable expansions have been observed in regions such as Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh.

What are glacial lakes?

• The Himalayan arc is young and tectonically active, formed as a result of massive collision between Eurasia and the northward drifting Indian plate about 50 million years ago. It forms the northern limit of India. 

• The Hindu Kush–Karakoram–Himalayan region hosts the largest and most important glacier systems outside  the poles and is commonly referred to as the “Third Pole” on the Earth.

• A glacial lake is formed when a glacier erodes the land, and then melts, filling the depression created by the glacier.

• These bodies of water play a crucial role as freshwater sources for rivers in the Himalayan region.

• Glaciers across the globe have been experiencing unprecedented rates of retreat and thinning due to human-caused climate change.

• This retreat leads to the formation of new lakes and the enlargement of existing ones in the Himalayan region. 

The glacial lakes are categorised based on their formation process into four broad categories:

i) Moraine-dammed (water dammed by moraine)

ii) Ice-dammed (water dammed by ice)

iii) Erosion (water dammed in depressions formed by erosion)

iv) Other glacial lakes.

• Glacial lakes also pose significant risks such as Glacial Lake Outburst Floods (GLOFs), which can have devastating consequences for communities downstream.

Glacial Lake Outburst Flood (GLOF)

• Flash floods caused by the outburst of glacial lakes, called as Glacial Lake Outburst Flood (GLOF), are well known in the Himalayan region where such lakes had often been formed by landslides. 

• GLOFs have immense potential of flooding in downstream areas, causing disastrous consequences due to release of large volumes of water in a very short interval of time. 

• Glacial lakes release large volumes of meltwater due to the failure of natural dams, such as those made of moraine or ice, resulting in sudden and severe flooding downstream. 

• These dam failures can be triggered by various factors, including avalanches of ice or rock, extreme weather events, and other environmental factors.

• Most often, the consequences arising out of such situations are highly unpredictable primarily due to lack of availability of sufficient data regarding rainfall intensity, location of landslide, impounded volume and area and physical conditions of lakes/ water bodies. 

• GLOFs are not a new phenomenon but with the worldwide receding of glaciers and rising temperature the probability of their occurrences has risen in many mountain ranges.

• The frequency of GLOF events has been increasing since the second half of the 20th century due to the combined effects of climate change and deforestation.

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