Glacial Lake Outburst | UPSC

Glacial Lake Outburst | UPSC

      HEADLINES:

  • 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

      LEARNING: 

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 !

      ISSUE: 

The thawing of ice cores may accelerate in the future due to global warming, and there is an urgent need of better risk assessment and early warning.

  • 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.

KEY OBSERVATIONS

  • 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.

In some cases, cloudbursts can also trigger glacial lake outburst flood events like in the Kedarnath disaster in 2013.

  • 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.

Here the glaciers are located at high altitudes not lower than 5,200 m and most glaciers are of small size.

  • 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.

MONITORING LAKES

  • 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

A glacial lake outburst flood (GLOF) is a release of meltwater from a moraine– or ice-dam glacial lake due to dam failure.

  • 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).

DIRECT CAUSES

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)
  • Earthquake
  • 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

Glacial Lake Outburst | UPSC

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.

Today, GLOFs pose a risk downstream communities and infrastructure.

  • 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.

At the same time as human activities have expanded further into glaciated catchments.

  • The study of how GLOFs occur and their impacts is therefore important for future hazard mitigation.

GLACIAL LAKES

There are two main settings in which glacial lakes form:

  1. Behind moraine dams
  2. Behind ice dams.

MORAINE-DAMMED LAKES

  • 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.

As a glacier margin retreats, water collects in the topographic low between the ice-front and the abandoned frontal and/or lateral 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.

MORAINES

ICE-DAMMED LAKES

  • In contrast to moraine-dammed lakes, ice-dammed lakes form when drainage is blocked by a glacier that advances or becomes thicker.

Consequently, ice-dammed lake growth is closely related to glacier mass balance and climate.

  • Ice-dammed lakes form wherever a glacier blocks the drainage of meltwater.

OTHER FORMATIONS:

  • Where a tributary valley is blocked by a trunk glacier.

Where a glacier from a tributary valley advances across the main trunk valley.

  • In openings between the lateral glacier margin and ice-free valley sides.
  • At the point where two glaciers join.

Glacial Lake Outburst | UPSC

      IASbhai WINDUP: 

  • 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.

However, because moraine dams are normally destroyed in lake outbursts, the number of GLOFs will likely start to decrease over time, as the capacity for storing glacial meltwater is gradually lost.

     SOURCES:  THE HINDU | Glacial Lake Outburst | UPSC

 

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