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
34 THE OLD DRAINAGE OF THE SELLING-TSO - PANGGONG-TSO DEPRESSION.
There is much that appears in favour of this theory, much more than for the alternatives of an outflow by the Indus or the Satlej, especially as the canyons of the Satlej may easily have been eroded by this river itself, without the assistance of the Tsangpo. I have crossed the Photu-la or Kore-la twice, and standing on its saddle I said: We have mounted only 315 feet from the river to the Kore-la, where the height is 15,292 feet. And from the pass there is a headlong descent to the Kali Gandak, an affluent of the Ganges. By means of a canal cut through the Kore-la the uppermost Brahmaputra might be turned into the Ganges .... But the changes here indicated will some time come to pass without artificial aid, for the tentacles of the Kali Gandak are eating back northwards into the mountains much more quickly than the Tsangpo is eroding its valley. Some time or other, perhaps in a hundred thousand years, the Ganges system will have extended its tentacles to the bank of the Tsangpo, and then will be formed a bifurcation which, in the course of time, will bring about a total revolution in the proportions of the two rivers and their drainage areas.'
However, if the theories thus set forth by Burrard be admissible we would get a river much larger than the one I have presumed, taking its origin in the Tang-la mountains and arising to the Shayok and Indus by way of the Panggong lakes. And admitting differential movements of the crust, there would be nothing surprising in the fact that the Bogtsang-tsangpo now flows eastward while the Addantso and Chargut-tso also drain to the east.
There is, however, an alternative way of assuming the outflow from this long valley. The high degree of maturity of the Bo tsan -tsangPo points to great age. Even nowadays the Selling-tso is a recipient of rivers both from the east and west.
1,1
It is perhaps a more plausible theory that only the western section of the great Q
latitudinal valley drained to the Indus from a water-parting in the region of the
Shakangsham, and that the eastern section found an escape to the Nak-chu. The Sachu-
tsangpo would then, together with its tributary from the Shakangsham, have turned
in a very sharp bend from the region of the present Selling-tso eastwards via the lakes
Pongok-tso, Burben-tso and Ngamdo-tso-nak, from where it must have turned south-
ward to the Nak-chu. This second alternative has been adopted on the little map
of mountain ranges and ancient rivers at the end of this volume.
Whether the one or the other of these two theories is more likely to be correct
is not as important as is the existence of a depression running through the whole
of interior Tibet and having every appearance of a gigantic river-bed, disfigured, it
is true, by differential movements, by denudation and weathering and by the filling
up of its trough with immeasurable quantities of subaerial and aquatic sediments.
i Transhimalaya, Vol. II, p. 78.
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