IIIFカラー高解像度
国立情報学研究所 - ディジタル・シルクロード・プロジェクト
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| IIIFカラー高解像度 |
| Southern Tibet : vol.7 | |
| 南チベット : vol.7 |
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引用情報
498
be regarded as fairly well explored, although all of them would naturally have to undergo considerable corrections on a large-scale map.
The largest basins are Achik-köl, Ayagh-kum-köl, Panggong-tso, Selling-tso, Kyaring-tso and Tengri-nor, and we may feel pretty certain that no other basins of the same size remain to be discovered. But there are a large number of basins of the same size as the moderate or small ones in the table. If now the 56 basins of the table cover 276,050 sq. km. together, would it be likely that the number of basins covering the remaining 441,75o sq. km., not considered in the table, would be proportionate to those calculated? Or, in other words, that the self-contained area of Tibet would consist of 145 basins altogether? No, by no means! For my table contains only large well-defined basins, and between them there are certainly several hundreds, perhaps thousands of very insignificant basins.
As to the distribution of the basins it should be noticed that all the six largest basins are situated at the very edge of the Central Asiatic water-parting, and that the interior parts of the self-contained area are occupied only by moderate, small or insignificant basins. Even in the list where the examples are taken at random all over the area without outflow, we find the following law clearly expressed: the smaller the basins the greater their number. Only 2 basins are above 2 5,000 sq. km. in size; from I o,000 to 25,000 there are 4; from 5000 to 1 o,000 there are 1o; from 3 000 to 5 000 there are 12; from I 000 to 3 000 there are 21. Of those less than I 000 sq. km. in size I have entered only a few in the list. A look at the map in
I : 1000 000 will persuade the reader that their number could easily be augmented to a hundred or more, to which must be added all the still unknown basins. From the data given above I estimate that the number of basins with an area of more than woo sq. km. amounts to about 300, the basins from I to I 000 sq. km. being perhaps one or two thousand or even more.
Regarding the lakes the same law prevails. There are only 2 lakes of more than 1Soo sq. km.; 6 have from 500 to i800; II from 200 to Soo; 18 from wo to 2 00 ; and 19 less than 1 oo. In reality there are innumerable insignificant pools on the Tibetan plateau-land.
In basins where water runs from a fresh-water lake to a salt lake, my list only considers the area of the latter. A special category of lakes are those in a dying state, as e. g. Tabie-tsaka. Some lakes are intermittently and only temporarily fed by rains.
The relations between the areas of lakes and their basins are not regularly proportional. Though the Tengri-nor has an area of 1 900 sq. km., its drainage area is only I I, I00 sq. km., whereas the Kyaring-tso with a drainage of 1 2,400 sq. km. is not quite one third of the Tengri-nor in size. Here, of course, everything depends upon the configuration of the ground, and the relations are of a purely geo-morpho-' logical nature. My lake No. XVIII for instance, is situated in a valley between two
THE SELF-CONTAINED BASINS OF TIBET.
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