Southern Tibet : vol.7 / 684 ページ（カラー画像）

0684	Southern Tibet : vol.7
南チベット : vol.7

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 441,750 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 25,000 sq. km.
in size; from 10,000 to 25,000 there are 4; from 5000 to 10,000 there are 10; from
3000 to 5000 there are 12; from 1000 to 3000 there are 21. Of those less than
1000 sq. km. in size I have entered only a few in the list. A look at the map in
1:1000000 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 1000 sq. km. amounts to about 300, the basins from 1 to 1000 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 1800 sq. km.; 6 have from 500 to 1800; 11 from 200 to 500; 18 from 100
to 200; and 19 less than 100. 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 con-
siders 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 1900 sq. km., its drainage area
is only 11,100 sq. km., whereas the Kyaring-tso with a drainage of 12,400 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

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