O’zbekiston respublikasi oliy va o’rta maxsus ta’lim vazirligi mirzo ulug’bek nomidagi o’zbekiston milliy universiteti

LAND BENEATH THE ANTARCTIC ICE
Antarctica is the highest and coldest continent on the earth. It contains more than nine — tenths of the world's ice, spread out over an area one — and — half times the size of the USA. With an annual snowfall near the center of the continent equivalent to 2,5 centimeters of water, it is also one of the driest areas of the world. Because of the low temperatures — the coldest is -88°C — snow does not meit but has built up gradually to cover the land with an ice sheet whose average elevation of more than 1600 meters is twice that of Asia, the next highest continent. The small amount of exposed rock supports only the lowest forms of life. It is a barren and hostile place for man, full of an elemental beauty that is of great attraction to some people.

Surrounded by stormy seas Antarctica is remote. Yet in spite of its remoteness Antarctica has a great although still poorly understood influence on the rest of the world. By forming the biggest heat sink on earth it plays a significant role in determining global weather patterns and atmospheric circulation. Complete melting of the present ice sheet would raise level by about seventy metres. Cold water formed around the coast of Antarctica sinks to the bottom of the sea and flows out into the Atlantic, Pacific, and Indian Oceans, rejuvenating distant seas even north of the equator with oxygen and nutrients. In Antarctica there are mineral resources which one day will be economic to exploit. By being in an essentially uncontaminated environment, the chemical composition of the ice itself holds record of the past climatic changes and present pollution levels. In all these aspects² the ice cover is the dominant feature and for these reasons³ it is being studied by glaciologists from many countries.

In the exploration of Antarctica one of the fundamental questions asked is how thick is the ice sheet? Measurements of ice depths were carried out originally by seismic reflection shooting and gravity surveys. Seismology is used still for more specialized applications — looking at ice crystal anisotropy — and is the only way of gathering information about the character of rocks deep in the earth's crust under the ice but routine measurements of the ice thickness are now usually done by radio echo sounding. The advantage of this method is that it gives a continuous profile of the bedrock on which the ice rests, while simultaneously giving information on the character of the rock and on internal features within the ice. The use of radio echo sounding in the last ten years has increased greatly our knowledge and understanding of the geographical distribution of ice and the flow and behaviour of glaciers, ice sheets and ice shelves. In Antarctica continuous radio echo profiling has already revealed extensive mountain ranges buried by ice, large areas where the ice is resting on rock below sea level, and the presence of lakes beneath ice that is more than three kilometers thick. As data accumulate it becomes obvious that that under the featureless snow surface lies an area of truly great complexity and scientific interest that has only just been touched.
Notes

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