IIIF Color HighRes
National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Scientific Results of a Journey in Central Asia, 1899-1902 : vol.4 |
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Citation Information
| LACUSTRINE PROBLEMS. DESICCATION ETC. | 6o1 | |||
| These mountain-lakes nearly always contain fish, and their water is wonderfully transparent. Of course they vary in outline in conformity with the varying shapes of the adjacent mountains. Besides these there are a number of transitional lacustrine forms intermediate between the flat lakes and the mountain-lakes, belonging partly to the one type and partly to the other, e. g. the Selling-tso. Often too it happens that a lake which is properly a flat lake has steep mountains overhanging some part of its shores; this was the case with most of the lakes that I encountered in my latitudinal valley in I896. As an example of the group of annular lakes, I need only mention the Naktsong-tso and the Jamdok-tso. Their characteristic feature is indicated in the designation applied to them. In shape they make a more or less regular ring. Possibly there still remain several lakes of this peculiar type yet to be discovered. Their shape is prescribed by the small east-west mountain-ranges and the complete breaches effected through them whether by glacial or other agencies. It is of course self-evident, that the lakes of Tibet admit of being classified in various other categories. Two great divisions are the fresh-water lakes and the salt-water lakes, the latter constituting the great majority. The salt-water lakes again are divisible into several classes, such as those that are slightly saline, the class usually described on the English maps by the word »drinkable», and others exhibiting every possible degree of salinity. Thus the Lower Kum-köl is moderately salt; but the large salt lake of Camps XXX to XXXIII (1900) is one concentrated salt solution. The cause of this is, that the lake simultaneously with excessive shallowness possesses a very extensive evaporation surface, together with a copious inflow of fresh water. The Kum-köl, on the other hand, is relatively deep, and although the volume of water that enters it is large, yet in proportion to the total volume of the lake the evaporation surface is nevertheless relatively small. Those lakes possess an insignificant degree of salinity which receive only a scanty supply of water, as also those which, although they formerly enjoyed an outlet, are now, like the Panggong-tso, cut off and deprived of their outflow. In yet other lakes the salinity appears to be subject to periodical fluctuations every year, e. g. the Aru-tso. In the lakes that are destitute of outflow and yet show merely a trace of salinity, a temporary effluent may be predicated, in most cases subterranean. It is the commonest thing also to find Tibetan lakes occurring in pairs, in such wise that the upper one is fresh, while the lower one is salt. We encountered combinations of this kind in the Kum-köl, in the big salt lake and the lake lying to the west of it that is fed by glacier-water, and in the two fresh-water lakes at Camps XXXVIII—XLII, which empty themselves into an adjacent salt lake; while the Tso-ngombo and the Panggong-tso, and probably also Dutreuil de Rhins's Lacs Jumeaux, are other examples. In the Selling-tso system we have a whole family of intimately related lakes. In respect of their desiccation the Tibetan lakes may again be divided into several classes. In some the process is not descernible at all, whereas others have entirely disappeared; and between these two extremes there occur others at every possible degree of variation. In this connection again we may speak of temporary lakes, that is such as contain water only whilst the snows are melting, but after 76 Hedin, Tourney in Central Asia. IV. | ||||
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