Glacial Lake Outburst | UPSC
- Lessons from Ladakh’s glacial lake outburst
WHY IN NEWS:
- The cause was not spillover but rather a tunnelling drainage process.
- In a paper recently published in Natural Hazards, the team notes that this case study “illustrates the problem of potentially hazardous lakes being overlooked.”
SYLLABUS COVERED: GS 1 :Geography
For PRELIMS it is important to understand causes , consequences and different types of lakes setting .
For MAINS keep an eye on risk assessment . Note down the important threats . Let us dive in !
- In August 2014, a glacial lake outburst flood hit the village of Gya in Ladakh, destroying houses, fields and bridges.
- Using remote sensing data, researchers from Germany have mapped the evolution of Gya glacial lake and note the cause of the flood.
- It is almost certain that other glacial lake outburst floods will happen all over the Indian Himalaya.
- However, not all of these events have catastrophic outcomes.
- It largely depends on urban planning, the size of the lake, the distance between the lake and affected villages, the valley section and some more aspects.
- Different sections of the Himalaya the occurrence of such floods has received different attention.
- These events have been regarded as a major risk in the central Himalayan region including Sikkim.
- The arid Trans-Himalayan regions of Ladakh have received attention only recently.
- The glacial lakes are quite small in size.
- In the case of the Gya lake at 5,400 m, the lake is almost always ice-covered, even during summer.
- The team adds more bathymetric studies are needed to analyse lake volumes, and it is important to regularly monitor lake development and dynamics.
- New, sophisticated technologies can also be put to use to understand the stability of the moraines that dam the lake.
GLACIAL LAKE OUTBURST FLOOD
- GLOFs often result in catastrophic flooding downstream, with major geomorphic and socioeconomic impacts.
GLOFs have three main features:
- They involve sudden (and sometimes cyclic) releases of water.
- They tend to be rapid events, lasting hours to days.
- They result in large downstream river discharges (which often increase by an order of magnitude).
The following direct causes of glacial lake outburst floods were documented:
- Rapid slope movement into the lake
- Heavy rainfall/snowmelt
- Cascading processes (flood from a lake situated upstream)
- Melting of ice incorporated in dam/forming the dam (including volcanic activity-triggered jökulhlaups)
- Blocking of subsurface outflow tunnels (applies only to lakes without surface outflow or lakes with a combination of surface and subsurface outflow)
- Long-term dam degradation
SOURCE : WIKI COMMONS
WHY GLOF’s ARE IMPORTANT?
- Some of the largest floods in Earth’s history have been GLOFs.
- They have caused large-scale landscape change, and even altered regional climate by releasing huge quantities of freshwater to the oceans.
- In Peru alone, GLOFs were responsible for ~32,000 deaths in the 20th century.
- They have killed hundreds to thousands of people in other mountain regions (e.g. the Himalayas).
- GLOF’s have destroyed roads, bridges, and hydroelectric developments and critical infrastructure.
AN INCREASING HAZARD
- Importantly, the general global trend of glacier shrinkage through the 20th and 21st centuries has seen the number and size of glacial lakes increase.
- The study of how GLOFs occur and their impacts is therefore important for future hazard mitigation.
There are two main settings in which glacial lakes form:
- Behind moraine dams
- Behind ice dams.
- When a glacier retreats, it can leave behind a large impression in the ground that fills with water, turning it into a lake.This is typically known as a moraine.
- Moraine-dammed lakes form during periods of glacier retreat from a moraine.
- These lakes can be impounded by an unstable pile of debris and buried ice.
- Most existing moraine-dammed lakes were formed when mountain glaciers began to retreat from large moraine ridges constructed during the Little Ice Age.
- In contrast to moraine-dammed lakes, ice-dammed lakes form when drainage is blocked by a glacier that advances or becomes thicker.
- Ice-dammed lakes form wherever a glacier blocks the drainage of meltwater.
- Where a tributary valley is blocked by a trunk glacier.
- In openings between the lateral glacier margin and ice-free valley sides.
- At the point where two glaciers join.
- The threat from moraine-dammed GLOFs is typically greatest during periods of glacier retreat, whereas ice-dammed GLOFs are highest during periods of glacier growth.
- Therefore, it is expected that number of moraine-dammed GLOFs to increase as mountain glaciers continue to shrink worldwide.
SOURCES: THE HINDU | Glacial Lake Outburst | UPSC
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