GLACIAL LAKE OUTBURST FLOOD (GLOF)

 

A glacial lake outburst flood (GLOF) is a type of outburst flood that occurs when the dam containing a glacial lake fails. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a jökulhlaup. The dam can consist of glacier ice or a terminal moraine. Failure can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, volcanic eruptions under the ice, or massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.

Natural occurrence of GLOF environemnt

Glacial lakes are common in the high elevation of glacierised basin. They are formed when glacial ice or moraines or natural depressions impound water. There are varieties of such lakes, ranging from melt water ponds on the surface of glacier to large lakes in side valleys dammed by a glacier in the main valley.

Location of major GLOF sites in Himalayan range 

Elevation is the major factor behind creation of these type of lakes. Averagely in Himalayan point of view most of glacier lakes are found above than 4,000 to 6,000 meters. Valley or mountain glaciers are main source of feeding points for making glacier lakes. More than 6,000 meter elevation there are location of permanent glaciers there, it is not possible to make any glacier lake. Glacier lake are found and create lower than snow line that is almost 6,000 meters in the whole Himalayan mountain system ranging from east to west. After 4,000-5,000 meters High Himalaya’s ‘U’ shaped valley is starting to convert into ‘V’ shaped valley where very narrow type of landscape creates; glacier lake’s small neck size outlet drainage system start to move in the downward direction. During extreme winter these glacier lake gets totally freeze down therefore the size (horizontal and vertical both) begins to increase. In the month of February to March glacier lake start to develop cracks in the lake’s top or outside ice sheet, due to continuous increase in atmospheric temperature, glacier lake start to receive more water mass from melting ice water from upside. Therefore, glacier lake lost their capability to manage water mass and suddenly thin neck (downward margin of the lake) of the lake start to outburst and huge amount of water mass mixing with snow and rock boulders begins to roll down in the valley, which is very dangerous for the dwellers (villagers) and wild species, natural vegetation situated beside the river. This is very common natural phenomena in the entire Himalayan system on the same height. Where density of population is high damage will be high and in the scanty population region it will effect less. Here is some major GLOF occurred in the whole Himalayan system.

India: In 1929, a GLOF from the Chong Khumdan Glacier in the Karakoram caused flooding on the Indus River 1,200 km downstream (a maximum flood rise of 8.1 m at Attock).

On 7 February 2021, part of Nandadevi Glacier broke away, triggering a GLOF sweeping away a power plant. More than 150 people were feared dead.

Bhutan: GLOFs occur with regularity in the valleys and low lying river plains of Bhutan. In the recent past, flash floods have occurred in the Thimphu, Paro and Punankha-Wangdue valleys. Of the 2674 glacial lakes in Bhutan, 24 have been identified by a recent study as candidates for GLOFs in the near future. In October 1994, a GLOF 90 kilometres (56 mi) upstream from Punakha Dzong caused massive flooding on the Pho Chhu River, damaging the dzong and causing casualties.

In 2001, scientists identified Lake Thorthormi as one that threatened imminent and catastrophic collapse. The situation was eventually relieved by carving a water channel from the lip of the lake to relieve water pressure.

Nepal: Even though GLOF events have been occurring in Nepal for many decades, the Dig Cho glacial lake outburst, which took place in 1985, has triggered detailed study of this phenomenon. In 1996, the Water and Energy Commission Secretariat (WECS) of Nepal reported that five lakes were potentially dangerous, namely, Dig Tsho, Imja, Lower Barun, Tsho Rolpa, and Thulagi, all lying above 4,100 m. A recent study done by ICIMOD and UNEP (UNEP, 2001) reported 20 potentially dangerous lakes in Nepal. In ten of them GLOF events have occurred in the past few years and some have been regenerating after the event. Additional dangerous glacial lakes may exist in parts of Tibet that are drained by streams crossing into Nepal, raising the possibility of outburst incidents in Tibet causing downstream damage in Nepal. The Gandaki River basin is reported to contain 1025 glaciers and 338 lakes.

Thulagi glacier The Thulagi glacier, which is located in the Upper Marsyangdi River basin, is one out of the two moraine-dammed lakes (supra-glacial lakes), identified as a potentially dangerous lake. The KfW, Frankfurt, the BGR (Federal Institute for Geosciences and Natural Resources, Germany), in cooperation with the Department of Hydrology and Meteorology in Kathmandu, have carried out studies on the Thulagi Glacier and have concluded that even assuming the worst case, a disastrous outburst of the lake can be excluded in the near future.

Tibet: Longbasaba and Pida lakes are two moraine-dammed lakes at an altitude of about 5700 m in the Eastern Himalayas. Due to the rise of temperature, the areas of the Longbasaba and Kaer glaciers decreased by 8.7% and 16.6% from 1978 to 2005. Water from glaciers directly flowed into Longbasaba and Pida lakes, and the area of the two lakes increased by 140% and 194%. According to the report of the Hydrological Department of Tibet in 2006, if a GLOF had occurred at the two lakes, 23 towns and villages, where more than 12,500 people live, would have been endangered.

In Tibet, one of the major barley producing areas of the Tibetan Plateau was destroyed by GLOFs in August 2000. More than 10,000 homes, 98 bridges and dykes were destroyed and its estimated cost was about $75 million. The farming communities faced food shortages that year by losing their grain and livestock.

A major GLOF was reported in 1978 in the valley of the Shaksgam River in the Karakoram, a part of historic Kashmir, ceded by Pakistan to China.

Recent GLOF occurrence of Nandadevi Glacier: 

On 7 February 2021, part of Nandadevi Glacier broke away, triggering a GLOF sweeping away a power plant. The Nanda Devi glacier forms part of the second-highest mountain in India - the Nanda Devi Mountain. While it the second-highest after Kangchenjunga, it is the highest mountain located entirely within the country as Kangchenjunga lies on the border of India and Nepal. 

Glacier lake formation due to melting of glaciers in the upper catchment regions

Natural Glaciers developed over the frozen lake

After the flash flood event situation of the river valley (blowing of icesheets with flash flood)

On the northern side of the Nanda Devi lies the Uttari Nanda Devi Glacier which flows into the 'Uttari Rishi Glacier'. To the southwest lies the Dakkhini Nanda Devi Glacier which flows into the Dakkhini Rishi Glacier. All of these glaciers drain west into the Rishiganga. 

Flash flood also affected the downstream hydro project of National Thermal Power Corporation Limited at Tapovan on the river Dhauliganga, which is a tributary of the river Alaknanda. More than 150 labourers working in the power project are missing. Environment experts have called for a review of power projects in the ecologically sensitive mountains.

There is no danger of downstream flooding and the rise in water level has been contained, as per the information given by the Central Water Commission,” says the government. “There is also no threat to the neighboring villages. At the same time, the concerned agencies of the Centre and the State were asked to keep a strict vigil on the situation.

GLOF in the Chamoli valley, Uttarakhand 

Destroyed dam near Chamoli in Uttarakhand after GLOF event

GLOF of Chamoli in print media

This kind of GLOF occurrence need to continuous monitor by scientist community. There are number of site which could be convert into GLOF disaster in many places where potential glacier lake develops particularly during end of the winter. 

  

REFERENCES:

1.     Hewitt, K. (1982) Natural dams and outburst floods of the Karakoram Himalaya Archived 21 July 2011 at the Wayback Machine.

2.     150 NTPC workers missing after glacier triggers flood in Uttarakhand". mint. 7 February 2021. Retrieved 7 February 2021.

3.     Chhopel, Karma (15 March 2006). "Flash Floods and Debris Flows due to Glacial Lake Outburst Floods" (ppt). Proceedings of the International Workshop on Flash Flood Forecasting coordinated by the U.S. National Oceanic and Atmospheric Administration's National Weather Service and the World Meteorological Organization, San José, Costa Rica, March 2006. Conference web site (NOAA), Abstract (pdf). Thimphu, Bhutan: Hydro-Met Services Division, Dept. of Energy, Ministry of Trade and Industry.

4.     Wangda, Dorji (9 September 2006). "GIS Tools Demonstration: Bhutan Glacial Hazards" (PDF). Proceedings of the LEG Regional Workshop on NAPA coordinated by UNITAR, Thimphu, Bhutan, September 2006. Conference web site (UNITAR). Dept, of Geology and Mines, Govt. of Bhutan. Archived from the original (PDF) on 24 August 2006.

5.     Leslie, Jaques (17 June 2013). "A Torrent of Consequences"(article). World Policy Journal, New York, Summer 2013. New York City: World Policy Institute.

6.     BGR/NLfB/GGA: Gletschersee Thulagi Archived 18 July 2011 at the Wayback Machine.

7.     Xin, Wang; Shiyin, Liu; Wanqin, Guo; Junli, Xu (2008). "Assessment and Simulation of Glacier Lake Outburst Floods for Longbasaba and Pida Lakes, China". Mountain Research and Development. 28 (3/4): 310–317. doi:10.1659/mrd.0894.

8.     WWF Nepal Program. "An Overview of Glaciers, Glacier Retreat, and Subsequent Impacts in Nepal, India and China". 14 March. 2005

ICIMOD, Kathmandu, NEPAL (for the animated video) - https://www.youtube.com/watch?v=awLGxl5JmjY

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