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Himalayas , Climate And Nepal
By DR. AB THAPA
According to the recent theory of plate tectonics the Indian plate moved north against Eurasia and pushed up the thick pile of geosynclinal sediments in the Tethyan sea in between and formed the Himalayan range. The Himalayan range has a great influence upon the climate of Asia and also the Northern Hemisphere, since its topography has a direct bearing on the atmospheric circulation. Thus the pattern of rainfall, temperature and wind velocity in Nepal and Indian Sub-continent is greatly influenced by the Himalayan mountains.
The formation and development of the glaciers in the Himalayas depends on the hydrological cycle related to the atmospheric circulation. Therefore, the glaciological studies of these glaciers are important step towards better understanding of the relation of glacier variations to climatic changes. It is very important to know the state of glaciers in the Himalayas and their current variations in order to understand the relation between glaciers and the climate and also water resources development.
Need for the glaciological studies of the Himalayas had been felt since a long time. In 1973, in cooperation with the International Hydrological Decade (IHD) 1965-1974, which was promoted by the UNESCO, observation studies of the glaciers in the Himalayan mountains within the Nepal territory were initiated by the Japanese Society of Snow and Ice. The studies were rewarded with good results. In 1980s, Royal Nepal Academy of Science and Technology (RONAST) was striving to set up an international center for the study of snow and ice primarily concerned with the glaciological studies in the Himalayas to promote sustainable economic and social development in Nepal and in adjacent countries. .
Himalayan Glaciers
Glaciers occur exclusively in mountainous regions above the snow line. Mountains below the snow line only carry seasonal snow. Precipitation occurring at great heights gets solidified as snow. All the great peaks of Himalayan mountains are , therefore, covered with snow. The snowline, the lowest line on a mountain at which snow exists throughout the year, is about 5,490 m at the equator and only 610 m in Greenland .
As successive snowfalls occur, pressure on the lower layers increases and the snow becomes granular ice. When the weight of ice increases, the depth of ice being more than a critical value, it begins to move and is known as a glacier. The movement is attributed to the lubrication effect produced by water which exists at the bottom-most layer of the glacier as ice (occupying more volume than water) turns into water under pressure. When the volume is decreased due to pressure, water is formed. The rate of movement of the glaciers per year varies considerably.
The snow line of the Mount Everest is approximately 5,800 to 6,000 meters above the sea level, but the mountain rises 3,000 meters above the snow line, where snow accumulates and glaciers originate. Constant avalanches of snow from the slopes feed the upper reaches of the glaciers, and, as a result, the surface layers of ice and snow grow increasingly thicker. The glaciers begin to slide under this weight and enter the valleys like tongues of moving ice. In that part of the glacier, which is below the snow line, the ice melts and evaporates (the ablation zone). Because ablation and intake of ice at the glacier tongue are generally in equilibrium, the positions of the termini of the glaciers are fairly constant..
Classification of Glaciers
According to the classification of glaciers proposed by Watanabe; Endo and Ishida (1967), the glaciers in the Nepal Himalayas can be classified into two groups – Nepal type glaciers and Tibet type glaciers. The Nepal type glaciers are located on the southern slope of the Great Himalayas, and the Tibet type glaciers on the northern slope. The lowest elevation of the glaciers of the former type is lower than that of the latter type. The length of the glaciers of the former type is longer than that of the latter type. In the case of the both types, it is found that the length of glaciers in the Nepal Himalayas is longer in eastern Nepal than in western Nepal .
The glaciers formed at a temperature not far below its melting point are described as temperate or maritime. Owing to the higher temperature of the ice, its pronounced plasticity and its larger volume, the velocity of these glaciers is greater than that of the continental type. Whereas the flow of continental type glaciers generally does not exceed 100 meters a year, the temperate glaciers have been recorded as moving at a rate of 300 to 400 meters a year.
Tibetan Glaciers
Himalayas are in effect a huge barrier that arrests the wet monsoons of the Indian Ocean from the south, leaving the interior of the Tibetan Plateau extremely cold and dry and snow accumulations on the glaciers very scant. The water equivalent of the annual snowfall is only about 500 to 800 mm. Such a thin layer of snow melts rapidly in the summer. In such circumstances perennial snow can stay and glaciers appear only at very high altitudes where the temperature is very low. The snow line on the northern slopes of the Himalayas reaches 6,200 meters, the highest yet found in the northern hemisphere. The glaciers here exist only because of the extremely low temperatures. They are therefore referred to as cold or continental glaciers. In sharp contrast, snow falls in abundance in the vicinity of the bend of the Brahmaputra in the southern part of the Tibet , owing to the influence of the Indian Ocean ’s monsoons. The annual layer of neve snow in this part of the Plateau often reaches 2,000 to 3,000 mm in water equivalent. This substantially lowers the snow line. In the Bomi-Zayu area in southern Tibet , the snow line is frequently between 4,500 to 4,800 meters, more than 1,000 meters lower than in the Mount Everest region.
Climate
The most overwhelming aspect of the Himalayan environment is the cold. In January, the coldest month of the year, the average temperature at an altitude equal to that of the summit of the Mount Everest is about – 36 C, and it may drop to an extreme of - 60 C. Even in the warmest month July, the average temperature is – 19 , and at no time of the year does it rise above freezing. The intense solar radiation that brings welcome warmth, however, is in itself a hazard. The strong ultraviolet rays and the dazzling reflections from snow and ice present the constant danger of red and swollen eyes, unbearable pain and even snow blindness to a climber without sunglasses.
The glittering, fantastic landscapes of the Himalayan peaks are as beautiful as any on earth, but alien as any on the moon. Man, attempting to assault the heights of the Mount Everest or any other high peaks, can survive only with the help of modern technology by overcoming for a brief time the three deadly natural obstacles - cold, wind, and rarified air.
As for the wind, the second great difficulty with which the mountaineers have to face. Only in the month of October, and again from March to May, is the weather sufficiently calm enough for climbing. From June to September, the Himalayan region is under the influence of the monsoons that blow in from the Indian Ocean . The mountain tops disappear in the seas of clouds, and violent snowstorms are too frequent. From November to February, the global southwest jet stream moves in from the north, battering the high summits with winds of hurricane force that may reach a velocity of about 90 meters per second. Anybody facing the winds of this speed would be subjected to a pressure of 100 kilograms. Even in the summer climbing season suddenly strong winds may arise. When a storm comes up, often whirling not only snow and ice but also sand and stones, the climbers would be facing unimaginable hardships and the greatest danger.
Water Resources
The Himalayas comprises one of the mountain areas of the world where water supply from glacier melting plays a significant economic role. The glaciers of the Himalayas act as reservoirs of frozen water. They are the fountainheads of several large rivers. Among them are the major rivers flowing into the South Asia - the Indus, Sutlez, Ganges, Karnali, Kali-Gandak, Arun, Brahmaputra and few others.
With the advent of summer, the glaciers release meltwater to swell the rivers and streams. Glaciers melt during the hot months( March to June) and give rise to large summer flows in the Himalayan rivers.
In Conclusion
The state of a glacier in relation to its geographical position is an important indicator of climate and the variation of glaciers accordingly provides a measure of climatic trends. In addition, glaciological observations in the Himalayas are also of critical importance to a fuller assessment of the water resources and their more rational use to provide water for irrigation, hydro-power and domestic supplies. As basic data for this purpose, the amount, distribution and variation of glaciers and their melting processes should be continuously observed in the glaciated areas. An international center devoted to glaciological studies of the Himalayas could help to promote sustainable economic and social development in Nepal and in adjacent countries.
(Dr. Thapa writes on water resources)
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