A glacier break is suspected to have caused the flash floods in Uttarakhand Chamoli on Sunday. Dozens of people are missing and feared dead after a piece of a Himalayan glacier fell into a river and triggered a huge flood in northern India. The floodwaters burst open a dam and a deluge of water poured through a valley in the state of Uttarakhand. Many villages were washed away by flood waters. Many other have been evacuated, but officials warned more than 300 people may have been caught in the torrent. So for bodies of 30 people have been recovered. Video showed the floodwater barreling through the area, leaving destruction in its wake. One witness said a wall of water and rock sped down the Dhauliganga river so quickly there was no time to sound the alarm.The remoteness of where this happened means no-one has a definitive answer, so far.Experts say one possibility is that massive ice blocks broke off the glacier due to a temperature rise, releasing a huge amount of water.That could have caused avalanches bringing down rocks and mud. Experts say an avalanche could also have hit a glacial lake which then burst. Another possibility is that an avalanche or landslide may have dammed the river for some time, causing it to burst out after the water level rose.Environmental experts have attributed the glacial melt to global warming. Glacier retreat and permafrost thaw are projected to decrease the stability of mountain slopes and increase the number and area of glacier lakes, according to the latest assessment reports of the UN Intergovernmental Panel on Climate Change.There is also high confidence that the number and area of glacier lakes will continue to increase in most regions in the coming decades, and new lakes will develop closer to steep and potentially unstable mountain walls where lake outbursts can be more easily triggered.Climate change has driven erratic weather patterns like increased snowfall and rainfall, warmer winters has led to the melting of a lot of snow. The thermal profile of ice, say experts, was increasing. Earlier the temperature of ice ranged from -6◦C to -20◦C, it is now -2◦C making it more susceptible to melting.
What are GLOFs and how vulnerable are the Himalayas?
When glaciers melt, the water in glacial lakes accumulates behind loose, natural “glacial/moraine dams” made of ice, sand, pebbles and ice residue. A GLOF (A glacial lake outburst flood) refers to the flooding that occurs when the water dammed by a glacier or a moraine is released suddenly. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a Jokulhlaup. 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.Unlike earthen dams, the weak structure of the moraine dam leads to the abrupt failure of the dam on top of the glacial lake, which holds large volume of water. A failure of the dam has the potential of releasing millions of cubic metres of water in a short period, causing catastrophic flooding downstream. Peak flows as high as 15,000 cubic metre per second have been recorded in such events. According to NDMA (National Disaster Management Authority), glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs. Since glaciers in the Himalayas are in a retreating phase, glacial lakes are growing and pose a potentially large risk to downstream infrastructure and life. An “Inventory and Monitoring of Glacial Lakes / Water Bodies in the Himalayan Region of Indian River Basins”, sponsored by Climate Change Directorate, Central Water Commission, and done by National Remote Sensing Centre during 2011-15, found that there are 352, 283 and 1,393 glacial lakes and water bodies in the Indus, Ganga and Brahmaputra basins respectively.
How can the risk be reduced?
The NDMA (National Disaster Management Authority) guidelines say that risk reduction has to begin with identifying and mapping such lakes, taking structural measures to prevent their sudden breach, and establishing 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 use of Synthetic-Aperture Radar imagery to automatically detect changes in water bodies, including new lake formations, during the monsoon months. It has said 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. A landslide occurred along the Phuktal (tributary to Zanskar river) on December 31, 2014 in Kargil district of Ladakh, leading to a potential flood situation on May 7, 2015. The NDMA created an Expert Task Force which, along with the Army, used explosives to channel water from the river using controlled blasting and manual excavation of debris.
(The author is a teacher by profession and is presently posted at Govt High School Brakpora Anantnag. Views are his own)
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