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lume). In 1952 Welch suggested a definition of size distinguishing between lake


and pond. According to it, the lake is "an area of open, relatively deep water, sufficiently large to produce somewhere on its periphery, a barren wave- swept shore", while the pond is a "very small, very shallow body of standing water in which quiet water and extensive occupancy by higher aquatic plants are common characteristics". In our opinion, the definition of the lake should not be subject to size, depth and annual variability, because these are characteristic features that shape the huge variety of lakes.


In terms of their formation, lakes may be grouped into, natural lakes


with a great many genetic types of lake basin (formed by tectonic, volcanic, gla- cial, karst, fluviale, marine and wind action, etc.), and artificial lakes created to meet various needs (power generating, fresh water and industrial water supply, navigation, fish farming, agreement, flood control, etc). Numerous classifications have been made by geomorpholo-


gists ,geologists and biologist, W.M., Davis (1882), for instance, grouped lake basins according three natural processes-constructive, destructive and ob- structive. A few years later, I.C.Russel (1895), considering Davis’ classifica- tion incomplete, put forward another division ‘basedon material agencies which produce depressions in the earth’s surface’ nine geological and one organic. Much later, in 1957, E. Hutchinson recognized 11 major genetic pro- cesses which produce a total of 76 different lake types selected from all the con- tinents of the Earth and provide the best international outlook on lake classifi- cation available. Space precludes the enumeration of the Hutchinson's 76 types; however, we shall review in brief 11 categories of natural processes involved in the formation of lake basins. Tectonic lake basins. Faulting is a major result of tectonic activity and is


responsible for the origin of important lake basins (e.g. lakes Baikal, the world’s deepest lake, Tanganyika, Nyasa, Albert and Victoria). Submarine structural ba- sins or depressions may become lakes when uplifted above sea level, or isolated from the sea ( e.g. Caspian Sea, Aral, Chad, Eyre, Great Salt Lake, Balaton and Neuesiedler). Lake basins produced by volcanic activity. There are three dominant


types among the 13 volcanic group: crater, caldera and dam lakes. The lakes formed in craters are small, because these depressions are changed (enlarged) by explosions, giving birth to calderas. The latter contain the great majority of lakes (e.g.Crater Lake, from Oregon, which is classical caldera). Many such lakes occur in the Central Massif of France, central Italy, Japan, the Philippines, Indonesia and New Zeeland). Volcanic dam lakes are the work of lava barring some valleys (e.g. Chambon, d'Aydat, Cassiere from the Central Massif in France). Lake basins produced by landsliding. These are formed in the val-


leys dammed by the superficial movement of earth materials, but since the 35


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