Glacial Lake Outburst Floods (GLOFs)
Vimal Khawas
The global climatic change during the second half of the twentieth century has brought about tremendous impact on the high mountainous glacial environments across the globe. The recent report compiled by the WWF Nepal Programme ‘An Overview of Glaciers, Glacier Retreat, and Subsequent Impact in Nepal, India and China’ seriously warns the people and policy makers in this context and the associated vices brought about glacier melting. The report points out that Himalayan Glaciers were receding at the rate of 10-15 meters per year on average and ironically were accelerating with increase in global warming. The receding rate is regarded as among the fastest in the world that severely threatens natural resource bases including water shortages in India, China and Nepal.
More dangerously, the report highlights that the Gangotri Glacier has been receding at an average rate of 23 meters per years in the last three decades. Further, observations, by geo-scientists, have led to the detection of various rates of glacial retreat in different parts of the Eastern India Himalayan region as well. In this connection it is observed that the Zemu Glacier of North Sikkim has been retreating at the rate of 8 meters per year while the ‘Kanchenjunga Massive’ in North Sikkim is behaving differently from those of the adjoining areas in recent times.
Box 1: Glacial Retreat and Advance
Glaciers originate in the high mountains where the snow budget is positive i.e. where the winter accumulation exceeds summer ablation. In such areas snow continues to grow year after year, and when the net accumulation in an area exceeds about 50 meters in thickness, the snow gradually changes into firn and then into ice through various processes of metamorphism, crystallization, melting and refreezing etc. The snow and ice ultimately fill up the snowfield and over flow down the preexisting stream valleys as mountain/valley glaciers. The snout of the glacier invariably descends well below the snow line, the lowest limit of perpetual snow, as a contrary to some prevalent conceptions and modifies topography initially produced mainly by fluvial action. This is the process by which the glaciations in the Himalaya and other high mountains of the world took place in the past. If the summer ablation in an area exceeds the winter accumulation of snow for several years or decades in succession, then the glacier and the snowfield start shrinking. Accumulation and ablation of snow in an area depends primarily on temperature and humidity of the atmosphere. Advance and retreat of the glaciers thus results from global and/or local changes of weather and climate. Such variations therefore, may be regarded as a reflection of changes in the atmospheric conditions of the earth as well as the area where it is taking place. (Bandhyopadhyay, M.K., 1998, Glacier Variation in the Himalaya, Geographical Review of India, Vol. 60, No.4, Pp. 381-391)
One of the most threatening impacts of glacial melting and subsequent retreat has been the Glacial Lake Outburst Floods (GLOFs). They are catastrophic discharges of water resulting primarily from melting glaciers. Many of the big glaciers have melted and retreated rapidly and have given birth to the origin of a large number of glacier lakes. Due to the faster rate of ice and snow melting, caused by the global warming, the accumulation of water in these lakes has been increasing rapidly and resulting sudden discharge of large volumes of water and debris and causing flooding in the downstream. An accelerated retreat of the glaciers in recent times has led to an enlargement of several glacial lakes. As the glaciers retreat they leave a large void behind. The ponds occupy the depression earlier occupied by glacier ice. These dams are structurally weak and unstable and undergo constant changes due to slope failures, slumping, etc. and run the risk of causing GLOFs.
Characterised by sudden releases of huge amounts of lake water, which in turn would rush down along the stream channel downstream in the form of dangerous flood waves, GLOF waves comprise water mixed with morainic materials and cause devastation for downstream riparian communities, hydropower stations and other infrastructure. Further, Glacial lake outburst flood (GLOF) causes disasters to life and property along the downstream, results serious death tolls and destruction of valuable forests, farms and costly mountain infrastructure.
There has been a frequent and alarming occurrence of GLOFs in and around the Himalayas. It has been observed that the frequency of the occurrence of GLOF events has been increasing in the second half of the twentieth century. GLOFs have cost lives, property and infrastructure in India, Nepal and China. Glacial Lake Out-burst Floods (GLOF) are the main natural hazards in the mountain areas of this region. A 1964 GLOF in China destroyed many kilometers of highway and washed 12 timber trucks 71 km from the scene. An outburst of Zhangzangbo Lake in 1981 killed four people and damaged the China-Nepal Friendship Bridge in the northern border, seven other bridges, a hydropower plant, Arniko highway and 51 houses. The damage was estimated to be USD 3 million. The 1985 GLOF at Dig Tsho was triggered by a large avalanche. A hydroelectricity project, 14 bridges, 30 houses and farmlands worth USD 4 million were destroyed. In 1998, the outburst of Tam Pokhari in Nepal killed two people, destroyed more than six bridges and washed away arable land. Losses worth over 150 million rupees have been estimated. A high water level was observed even after 19 hours in the Koshi barrage near the Indo-Nepal border. The river reverted to its original flow only after three days. There are about 159 glacier lakes in Koshi basin. Nearly 229 glacier lakes were identified in Tibet’s Arun basin, out of which 24 are potentially dangerous. Since 1935 more than 16 GLOFs have been reported which either occurred or extended into Nepal. This is a serious potential hazard that needs a thorough study on the Glaciology of the region before things go out of our control.
The solution of such problems is not so easy. Local steps like checking deforestation and overgrazing in the high altitude areas may not be sufficient enough to check glacial melting. This is a global problem and needs a global action. We, however, need to act in our own way to check global warming and at the same time keep in touch with other counterparts and see how they react to the problem. It is also that, all scientists associated with the geo-science should come together and work in close cooperation in the interdisciplinary problem of glacier variation with the aim of saving humanity from approaching disaster. Accurate and timely information on the spatial locations and regular monitoring of the glacier lakes' behavior is needed, to supervise and check the GLOF hazards and also assess the damages to be occurred in the near future. Modern information tools such as Remote Sensing and GIS could play a lead role in identifying potential risk lakes and monitoring the GLOF events in near real time.
**Associate Fellow, Council for Social Development, New Delhi. vimalkhawas@gmail.com**
The global climatic change during the second half of the twentieth century has brought about tremendous impact on the high mountainous glacial environments across the globe. The recent report compiled by the WWF Nepal Programme ‘An Overview of Glaciers, Glacier Retreat, and Subsequent Impact in Nepal, India and China’ seriously warns the people and policy makers in this context and the associated vices brought about glacier melting. The report points out that Himalayan Glaciers were receding at the rate of 10-15 meters per year on average and ironically were accelerating with increase in global warming. The receding rate is regarded as among the fastest in the world that severely threatens natural resource bases including water shortages in India, China and Nepal.
More dangerously, the report highlights that the Gangotri Glacier has been receding at an average rate of 23 meters per years in the last three decades. Further, observations, by geo-scientists, have led to the detection of various rates of glacial retreat in different parts of the Eastern India Himalayan region as well. In this connection it is observed that the Zemu Glacier of North Sikkim has been retreating at the rate of 8 meters per year while the ‘Kanchenjunga Massive’ in North Sikkim is behaving differently from those of the adjoining areas in recent times.
Box 1: Glacial Retreat and Advance
Glaciers originate in the high mountains where the snow budget is positive i.e. where the winter accumulation exceeds summer ablation. In such areas snow continues to grow year after year, and when the net accumulation in an area exceeds about 50 meters in thickness, the snow gradually changes into firn and then into ice through various processes of metamorphism, crystallization, melting and refreezing etc. The snow and ice ultimately fill up the snowfield and over flow down the preexisting stream valleys as mountain/valley glaciers. The snout of the glacier invariably descends well below the snow line, the lowest limit of perpetual snow, as a contrary to some prevalent conceptions and modifies topography initially produced mainly by fluvial action. This is the process by which the glaciations in the Himalaya and other high mountains of the world took place in the past. If the summer ablation in an area exceeds the winter accumulation of snow for several years or decades in succession, then the glacier and the snowfield start shrinking. Accumulation and ablation of snow in an area depends primarily on temperature and humidity of the atmosphere. Advance and retreat of the glaciers thus results from global and/or local changes of weather and climate. Such variations therefore, may be regarded as a reflection of changes in the atmospheric conditions of the earth as well as the area where it is taking place. (Bandhyopadhyay, M.K., 1998, Glacier Variation in the Himalaya, Geographical Review of India, Vol. 60, No.4, Pp. 381-391)
One of the most threatening impacts of glacial melting and subsequent retreat has been the Glacial Lake Outburst Floods (GLOFs). They are catastrophic discharges of water resulting primarily from melting glaciers. Many of the big glaciers have melted and retreated rapidly and have given birth to the origin of a large number of glacier lakes. Due to the faster rate of ice and snow melting, caused by the global warming, the accumulation of water in these lakes has been increasing rapidly and resulting sudden discharge of large volumes of water and debris and causing flooding in the downstream. An accelerated retreat of the glaciers in recent times has led to an enlargement of several glacial lakes. As the glaciers retreat they leave a large void behind. The ponds occupy the depression earlier occupied by glacier ice. These dams are structurally weak and unstable and undergo constant changes due to slope failures, slumping, etc. and run the risk of causing GLOFs.
Characterised by sudden releases of huge amounts of lake water, which in turn would rush down along the stream channel downstream in the form of dangerous flood waves, GLOF waves comprise water mixed with morainic materials and cause devastation for downstream riparian communities, hydropower stations and other infrastructure. Further, Glacial lake outburst flood (GLOF) causes disasters to life and property along the downstream, results serious death tolls and destruction of valuable forests, farms and costly mountain infrastructure.
There has been a frequent and alarming occurrence of GLOFs in and around the Himalayas. It has been observed that the frequency of the occurrence of GLOF events has been increasing in the second half of the twentieth century. GLOFs have cost lives, property and infrastructure in India, Nepal and China. Glacial Lake Out-burst Floods (GLOF) are the main natural hazards in the mountain areas of this region. A 1964 GLOF in China destroyed many kilometers of highway and washed 12 timber trucks 71 km from the scene. An outburst of Zhangzangbo Lake in 1981 killed four people and damaged the China-Nepal Friendship Bridge in the northern border, seven other bridges, a hydropower plant, Arniko highway and 51 houses. The damage was estimated to be USD 3 million. The 1985 GLOF at Dig Tsho was triggered by a large avalanche. A hydroelectricity project, 14 bridges, 30 houses and farmlands worth USD 4 million were destroyed. In 1998, the outburst of Tam Pokhari in Nepal killed two people, destroyed more than six bridges and washed away arable land. Losses worth over 150 million rupees have been estimated. A high water level was observed even after 19 hours in the Koshi barrage near the Indo-Nepal border. The river reverted to its original flow only after three days. There are about 159 glacier lakes in Koshi basin. Nearly 229 glacier lakes were identified in Tibet’s Arun basin, out of which 24 are potentially dangerous. Since 1935 more than 16 GLOFs have been reported which either occurred or extended into Nepal. This is a serious potential hazard that needs a thorough study on the Glaciology of the region before things go out of our control.
The solution of such problems is not so easy. Local steps like checking deforestation and overgrazing in the high altitude areas may not be sufficient enough to check glacial melting. This is a global problem and needs a global action. We, however, need to act in our own way to check global warming and at the same time keep in touch with other counterparts and see how they react to the problem. It is also that, all scientists associated with the geo-science should come together and work in close cooperation in the interdisciplinary problem of glacier variation with the aim of saving humanity from approaching disaster. Accurate and timely information on the spatial locations and regular monitoring of the glacier lakes' behavior is needed, to supervise and check the GLOF hazards and also assess the damages to be occurred in the near future. Modern information tools such as Remote Sensing and GIS could play a lead role in identifying potential risk lakes and monitoring the GLOF events in near real time.
**Associate Fellow, Council for Social Development, New Delhi. vimalkhawas@gmail.com**
posted by Vimal Khawas at 12:38 AM
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