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Uttarakhand's Chamoli district experienced massive floods on the morning of 7th February 2021. A large piece of ice with mud broke away from a glacier (suspected to be a part of the Nanda Devi Biosphere Reserve) in the Himalayas and fell into a lake that had been formed at its snout. The floods created due to the melting of this glacier also carried debris around the lake along with it as it rushed down the Rishi Ganga river with great force causing damage to lives and property. More than 152 people working inside tunnels to build two hydroelectricity projects downstream went missing, 25 were rescued and ten bodies were found. A number of bridges were washed away.
Studies over the last few years have continued to warn of the hazards like these in the Himalayas in the light of climate change and the impending glacier losses that have been happening in the fragile Himalayan region.
Glaciers are crucial for populations living in the Indo Gangetic plains. These slow-moving frozen rivers of ice in the Himalayas cater to the drinking water and agricultural needs of large sections of the population in the Indo-Gangetic plains.
Described as ‘nature’s bulldozers', these solid rivers melt gradually with rise in temperatures and pick up vegetation and silt that comes in their way while flowing creating snow bridges, gullies, glacial lakes, glacial troughs, icefalls, valleys, crevasses and moraines and cause major changes in the topography of the region as they descend forming rivers enriched with sediments.
According to the National Snow and Ice Data Centre, glaciers are formed due to the accumulation of snow over thousands of years. Glaciers form when snow remains in one location for a long time and then transforms into ice. The top layers of snow exert pressure on the lower layers transforming them into ice . What makes glaciers unique is their ability to flow like very slow rivers. Some glaciers are small, while others can be hundreds of kilometres in length.
Slow accumulation of snow is necessary for glacial ice to form. As thick layers of snow accumulate, the snowflakes buried deep below start getting tightly packed and rounded in shape gradually expelling most of the air trapped between the grains. These granular snow grains are called firn. As snow keeps accumulating, it exerts tremendous pressure on the layers of buried firn, and these grains begin to melt. The firn and meltwater slowly recrystallise to form glacial ice. This transformation process may take several decades to hundreds of years because the rate of glacial ice formation is highly dependent upon the amount of snowfall.
The thick mass of glacial ice begins to deform because of its own weight and causes the ice along the base of the glacier to melt because the temperature at which ice melts is reduced due to the pressure exerted by the weight of the glacial ice on the top. Heat from the Earth’s surface can also cause ice to melt along the base of the glacier.
As a result, a thin layer of meltwater accumulates between the basal ice and the Earth’s surface. The meltwater functions as a lubricant allowing the glacier to slide more readily over bedrock and sediments. If a lot of meltwater accumulates under the ice, the glacier may begin to advance very rapidly as a surge and is called as a galloping glacier that flows at a very rapid rate.
The area of glacial ice formation is called the zone of accumulation where more snow accumulates each winter than that which melts away during the summer. Glacial ice flows away from the zone of accumulation when the thick ice deforms under its own weight.
The area of a glacier that undergoes a large amount of melting is called the zone of wastage (zone of ablation). As the ice melts away, bits of sand and gravel on the surface of the glacier are left behind. This area gets replenished continuously as glacial ice continues to flow from the zone of accumulation.
The line that separates the zone of accumulation from the zone of wastage is called the snow line (equilibrium line). The upper surface of the glacier, where the ice does not undergo deformation, is referred to as the zone of fracture. In this zone, the ice is brittle and can crack, break or fracture. The end or toe of the glacier is called the terminus and is part of the zone of wastage. When the terminus of the glacier turns into a body of water, it also has some chunks of ice that float on the water and are known as icebergs.
The glacier grows when more glacial ice keeps forming in the zone of accumulation than melting in the zone of wastage. A glacier retreats when more ice melts away during the summer than that which forms during the winter. If the amount of glacial ice formation in the zone of accumulation equals the amount of melting in the zone of wastage, then the glacier does not advance or retreat.
While greenhouse gases are leading to a slow increase in global temperatures worldwide, this is leading to much higher rates of melting of ice than can be replenished, in recent years. And nowhere is this more evident than in the Himalayan region.
A recent 2019 study titled ‘Acceleration of ice loss across the Himalayas over the past 40 years’ published in the journal Science Advances that aimed studying the impact of climate change on glaciers in the Himalayas finds that glaciers across the Himalayas have experienced significant ice loss over the past 40 years, with the average rate of ice loss being twice as rapid in the 21st century as compared to the end of the 20th century.
The study also finds that all types of glaciers be them clean-ice, debris-covered and lake-terminating ones have undergone similar levels of ice losses. Altitude also plays an important role with debris covered glaciers showing slower thinning at lower elevations as compared to clean ice glaciers, but comparatively faster thinning in mid- to upper elevations. Lake-terminating glaciers concentrated in the eastern Himalayas show more thinning due to thermal undercutting and calving and they make up around 5 to 6 percent of the estimated total Himalaya-wide mass loss.
Another study titled ‘Hazard from Himalayan glacier lake outburst floods ‘ published in the journal Proceedings from the National Academy of Sciences (PNAS) has highlighted the hazards that can arise from the melting of glaciers in the Himalayan region. According to the study, the glacial melt in the Himalayas has been sustained and has gradually created more than 5,000 glacier lakes that are dammed by potentially unstable moraines (accumulations of dirt and rocks that have fallen on the glacier surface or have been pushed along by the glacier as it moves).
When such dams break, glacier lake outburst floods (GLOFs) can occur and cause catastrophic societal and geomorphic impacts as these can rival monsoon-fed discharges in major rivers hundreds to thousands of kilometres downstream. The study warns of future hazards from meteorological floods created from extreme runoffs during lake outbursts in the context of increasing population, infrastructure, and hydropower projects in the Himalayan headwaters.
The chapter ‘Water in the Hindu Kush Himalayas’ from the ‘The Hindu Kush Himalaya Assessment’ report by ICIMOD warns of the impending water crisis in the Himalayan regions due to fast melting of glaciers in the region due to climate change leading to an increase in water-related hazards such as floods in the area.
Though the flash floods in last week's Uttarakhand disaster were most likely caused due to climate change, their downstream impacts were worsened by dams and ill-planned road constructions. Two hydroelectricity projects, the Rishi Ganga and the Tapovan power projects were affected. Experts have long argued against the building of dams, tunnels and roads in the Himalayas due to its fragile ecology. However, dams and tunnels for hydroelectricity projects as well as roads continue to be constructed in much of the Hindu Kush Himalayas though they are being known to have a destabilising effect on mountain slopes.
Disasters like these point at the urgent need to review the current policies related to infrastructural projects that are being planned in the fragile and the ecologically sensitive Himalayan region.
Preparedness in the face disasters such as these, more focus on flood hazard studies, close monitoring of the Himalayan region and a review of the existing infrastructural projects with major changes at the policy level is the need of the hour!