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
LAKE DEPRESSIONS.
~~.
499
mighty mountain ranges, and it therefore occupies of its drainage basin. On
the other hand, my »Large lake» of 1901 which is situated on the flat and open plateau-land and which is surrounded by relatively low mountains at a considerable distance, occupies only -51u of its drainage area.
A careful examination of Colonel Byström's map in 1 : 1 000 000, which is the
most detailed and complete general map of Tibet in existence at the present date, will teach us that the lakes of the plateau-land are arranged in a certain degree of order, more especially in the northern and southern parts of the region. In the north we find two lines of lakes from west to east, viz., the Kwen-lun lakes, including my chain of lakes No. V—No. XX and the lakes of Wellby with their western continuation. This regular arrangement of the lakes is of great assistance to us in our attempts
to trace the situation and stretching of the principal mountain systems. For the lakes occupy the lowest parts of their basins, and a long series of lakes situated upon the same line, indicates a very extended depression. It is therefore natural, though not necessary, that a chain of lakes should be placed between two parallel mountain systems. In the same way Wellby's lakes let us suggest that their extended depression is bounded both to the north and south by parallel ranges.
In the south there are also two chains of lakes in depressions stretching through the whole plateau-land. In the northern one of these, to which Panggong-tso, Dagtse-tso and Selling-tso belong, NAIN SING, LITTLEDALE and I have travelled. The southern one is marked by Nganglaring-tso in the west and by Tengri-nor in the east.
The most central part of the plateau-land situated between Wellby's lakes in the north and the Panggong-tso—Selling-tso Lakes in the south is not sufficiently well known to allow us to trace such long lacustrine depressions as those just mentioned. This innermost part of Tibet has been crossed only on five lines by BOWER, DE RHINS, LITTLEDALE and myself. Our routes proceed from lake to lake, and it is probable that these lakes are also in reality placed upon more or less regular lines indicating long depressions between mountain ranges.
In my work Scientific Results, Vol. IV, p. 589 et seq. I have examined the absolute altitude of some 95 lakes discovered by NAIN SING, BONVALOT, BOWER, DE RHINS, LITTLEDALE, DEASY, RAWLING, WELLBY and myself As a mean altitude of 58 lakes in Eastern Tibet I got 48 I I m., and as the mean altitude of 37 lakes in western Tibet 4837 m., and I therefore arrived at the conclusion that the mean altitude of the general plane of the plateau-land was somewhat higher in the west than in the east. This is probably correct and most likely is due to the fact that the mountain ranges are more closely pressed together in the west than in the east.
It is more interesting, however, to examine the mean altitude of the lakes which belong to the same latitudinal valley. Taking, to begin with, the 1 2 Kwen-lun lakes of our list, their mean altitude amounts to 4891 m. The 6 lakes of Wellby
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