NDMA Guidelines on Glacial Lake Outburst Flood (GLOF)

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Context: A massive glacier burst at Chamoli in Uttarakhand yet again bringing back our focus to the dangers of climate change.

Prelims: Glaciers and rivers
Mains: GS-I, GS-III- About GLOF, Disaster preparedness and mitigation.

What happened?
  • Parts of Uttarakhand recently witnessed massive flooding after a chunk of the Nanda Devi glacier broke off at Joshimath in the Tapovan-Reni area of Chamoli District.
  • The glacial break led to a massive Flash Flood in Dhauli Ganga and Alaknanda Rivers, damaging houses and the nearby Rishiganga power project. 

  • Local authorities have described it as a glacial burst.
    • But it is unclear whether there was an avalanche in the area recently or whether the lake breach was the result of construction, anthropological activities, climate change, etc.
    • Scientists say this probably means that a gigantic chunk of ice broke away from a glacier and caused the water level in the associated glacial lake to abruptly rise and possibly trigger a “moraine breach event” — the breach of a natural dam made from rock and debris that has been holding the water back.
  • Past experiences:
    • 2013 Kedarnath calamity, the glacier break caused large-scale devastation in the upper reaches of the ecologically fragile Himalaya.
    • Another example: In 1929, a GLOF from the Chong Khumdan Glacier in the Karakoram caused flooding on the Indus River 1,200 km downstream 

What is Glacial Lake Outburst Flood (GLOF)?
  • A glacial lake outburst flood is a type of outburst flood occurring when water dammed by a glacier or a moraine is released. 
    • A water body that is dammed by the front of a glacier is called a marginal lake, and a water body that is capped by the glacier is called a sub-glacial lake.
      • When a marginal lake bursts, it may also be called marginal lake drainage.
      • When a sub-glacial lake bursts, it may be called Jaokulhlaup.

    • 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).
  • Glacial lake settings
    • There are two main settings in which glacial lakes form:
      • Behind moraine dams,
      • Behind ice dams.
  • Moraine-dammed lakes
    • 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.
    • Most existing moraine-dammed lakes (such as the Imja Tsho glacial lake in Nepal) formed when mountain glaciers began to retreat from large moraine ridges constructed during the Little Ice Age.

    • 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.
      • The  ice-dammed lakes include:
        • 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; and at the point where two glaciers join.


  • Impact of Climate Change:
    • Climate change has driven erratic weather patterns like increased snowfall and rainfall, warmer winters have led to the melting of a lot of snow.
    • According to the latest assessment reports of the UN Intergovernmental Panel on Climate Change, glacier retreat and permafrost thaw are projected to decrease the stability of mountain slopes and increase the number and area of glacier lakes.
What is a Flash flood?
  • A flash flood is a rapid inundation of geomorphically low-lying areas: washes, rivers, dry lakes, and basins.
  • These are highly localized events of short duration with a very high peak and usually have less than six hours between the occurrence of the rainfall and peak flood.
  • The flood situation worsens in the presence of choked drainage lines or encroachments obstructing the natural flow of water.
  • Causes of Flash floods
    • It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields.
    • However, floods are not always caused by heavy rainfall. Flash Floods can be caused by a number of things but is most often due to extremely heavy rainfall from thunderstorms.
    • Flash Floods can occur due to Dam or Levee Breaks, and/or Mudslides (Debris Flow).
    • In areas on or near glaciers, flash floods have also occurred, when glaciers have been melted.
    • The intensity of the rainfall, the location and distribution of the rainfall, the land use and topography, vegetation types and growth/density, soil type, and soil water-content all determine just how quickly the Flash Flooding may occur, and influence where it may occur.


NDMA guidelines and India's preparedness


  • Identify and Mapping Dangerous Lakes:
    • Potentially dangerous lakes are often identified.
    • This identification are going to be supported by field observations, past events, geomorphologic and geotechnical characteristics, etc.
  • Use of Technology:
    • It is recommended to utilize the Synthetic-Aperture Radar imagery.
    • It will automatically detect changes in water bodies, including new lake formations, during the monsoon months.
  • Structural Measures:
    • It recommends reducing the number of water with various methods to manage lakes structurally.
    • Methods are pumping or siphoning out water and making a tunnel through the moraine barrier or under an ice dam.
    • Constructions and development in High prone areas should be prohibited. it's a very efficient means to reduce risks at no cost.
  • Land Use Planning:
    • Land use planning regulations need to be developed.
    • In downstream areas, Infrastructure development should be monitored before, during, and after the construction.
  • Empowered Local Manpower:
    • Apart from specialized forces like NDRF, ITBP, and the military, there is a requirement for trained local manpower.
    • They can assist in planning and fixing emergency shelters, distributing relief packages, identifying missing people, and addressing the requirement for food, healthcare, water, sanitation, etc.
  • Early Warning System:
    • A robust early warning system in vulnerable zones should be put in place.
  • Emergency response team:
    • Quick Reaction Medical Teams, mobile field hospitals, Accident Relief Medical Vans, and heli-ambulances should be found out in areas inaccessible by roads.
  • How can the GLOF risk be reduced?
    • As per the NDMA guidelines that risk reduction has to begin with identifying and mapping such lakes, taking structural measures to prevent their sudden breach, and establishing a mechanism to save lives and property in times of a breach.
    • Potentially dangerous lakes can be identified based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam and surroundings, and other physical conditions.
    • NDMA has recommended the use of Synthetic-Aperture Radar imagery to automatically detect changes in water bodies, including new lake formations, during the monsoon months. Methods and protocols could also be developed to allow remote monitoring of lake bodies from space.
    • To manage lakes structurally, the NDMA recommends reducing the volume of water with methods such as controlled breaching, pumping or siphoning out water, and making a tunnel through the moraine barrier or under an ice dam.
  • How well is India prepared?
    • While some work on the identification of such lakes has been done by Central Water Commission (CWC), other aspects are still a work in progress like:
      • A robust early warning system, and
      • A broad framework for infrastructure development, construction and
      • Excavation in vulnerable zones.
    • In contrast to other countries, there are no uniform codes for excavation, construction, and grading codes in India.
    • Restricting constructions and development in GLOF/LLOF prone areas is a very efficient means to reduce risks at no cost.
    • The guidelines say the construction of any habitation should be prohibited in the high hazard zone.
      • Existing buildings are to be relocated to a safer nearby region and all the resources for the relocation have to be managed by Central/State governments.
      • New infrastructures in the medium hazard zone have to be accompanied by specific protection measures.
    • The guidelines emphasize the importance of land use planning:
      • There are no widely accepted procedures or regulations in India for land use planning in the GLOF/LLOF prone areas.
      • Such regulations need to be developed.
      • There should be monitoring systems prior to, during, and after the construction of infrastructure and settlements in the downstream area.
  • Are there early warning systems in place?
    • The number of implemented and operational GLOF EWS is still very small, even on a global scale.
    • In the Himalayan region, there are three reported instances (two in Nepal and one in China) of implementation of sensor- and monitoring-based technical systems for GLOF early warning.
    • India, though, has a remarkable history of successful warnings in relation to Landslide Lake Outburst Floods (LLOFs), dating back to the 19th century.
    • In 1894, a landslide in Gohna, Uttarakhand dammed the main river.
      • On July 5 that year, the engineer in charge estimated the lake would overflow the dam in mid-August, which eventually happened.
    • Despite the devastating impact of the flood, including washing away of most buildings along the river and severe destruction in Srinagar, no victims were reported, thanks to the precise prediction and the early warning to the population.
      • This was made possible by the installation of a telephone line between the lake and the downstream towns of Chamoli, Srinagar etc.
  • 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.
  • 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.
  • Therefore, we might expect the number of moraine-dammed GLOFs to increase as mountain glaciers continue to shrink worldwide.
  • 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.


Nanda Devi Glacier

  • Location: 
    • The glacier dwells on the Nanda Devi peak which is the second-highest mountain in the country after Kanchenjunga.
    • It is a part of the Garhwal Himalayas and is located in Chamoli district of Uttarakhand, between the Rishiganga valley on the west and the Goriganga valley on the east.
    • The glacier is located within the Nanda Devi Sanctuary and drains west into the Rishiganga.
    • Both Nanda Devi North and Nanda Devi South glaciers are 19 km in length and originated from the mountain peak which is 7,108 meters above sea level.

  • Nanda Devi glacier to Ganga
    • The melted water of the Nanda Devi glacier forms several streams and rivers. The water first flows into the Rishiganga river which later joins the Dhauliganga river.
    • It should be noted that Dhaulinganga is one of the tributaries of the river Ganga. Dhauliganga later merges into the Alaknanda river at Vishnuprayag.
    • The Dhauliganga river passes through places like Joshimath and Karnaprayag while Alaknanda flows through prominent regions like Uttarakhand's Srinagar, Haridwar, Ranikhet, Bhimtal, Haldwani, etc.

Dhauliganga River

  • It originates from Vasudhara Tal, perhaps the largest glacial lake in Uttarakhand.
  • Dhauliganga is one of the important tributaries of Alaknanda.
  • Dhauliganga is joined by the Rishiganga river at Raini.
  • It merges with the Alaknanda at Vishnuprayag.
  • There it loses its identity and the Alaknanda flows southwest through Chamoli, Maithana, Nandaprayag, Karnaprayag until it meets the Mandakini river, coming from the north at Rudraprayag.

Alaknanda River

  • Rise at the confluence and foot of the Satopanth and Bhagirath Kharak glaciers in Uttarakhand.
  • The five main tributaries joining with Alaknanda in order includes Dhauliganga, Nandakini, Pindar, Mandakini and Bhagirathi .
  • Alaknanda contributes a significantly larger portion to the flow of the Ganges than the Bhagirathi.
  • After the last tributary merging at Devprayag the river is known as the Ganges. 
  • Alaknanda then disappears and the mighty Ganga carries on its journey, first flowing south then west through important pilgrimage centers such as Rishikesh and finally descending into the Indo-Gangetic plains at Haridwar.

Several rivers in the Garhwal region merge with the Alaknanda at places called Prayag or 'holy confluence of rivers'.

  • These are:
    • Vishnuprayag, where the Alaknanda is met by the Dhauliganga River
    • Nandaprayag, where it is met by the Nandakini River
    • Karnaprayag, where it is met by the Pindar River
    • Rudraprayag, where it is met by the Mandakini River
    • Devprayag, where it meets the Bhagirathi River and officially becomes the Ganges

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